CONCENTRIC NETWORK CORP
S-1/A, 1997-07-31
TELEPHONE COMMUNICATIONS (NO RADIOTELEPHONE)
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<PAGE>
 
     
  AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JULY 31, 1997     
                                                     REGISTRATION NO. 333-27241
- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
 
                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549
 
                               ----------------
                                
                             AMENDMENT NO. 5     
                                      TO
                                   FORM S-1
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933
 
                               ----------------
                        CONCENTRIC NETWORK CORPORATION
            (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)
 
                               ----------------
        DELAWARE                     4813                    65-0257497
     (STATE OR OTHER          (PRIMARY STANDARD          (I.R.S. EMPLOYER
     JURISDICTION OF              INDUSTRIAL           IDENTIFICATION NUMBER)
    INCORPORATION OR          CLASSIFICATION CODE
      ORGANIZATION)                 NUMBER)
 
                               ----------------

                        CONCENTRIC NETWORK CORPORATION
                           10590 NORTH TANTAU AVENUE
                              CUPERTINO, CA 95014
                                (408) 342-2800
  (ADDRESS AND TELEPHONE NUMBER OF REGISTRANT'S PRINCIPAL EXECUTIVE OFFICES)
 
                               ----------------

                               HENRY R. NOTHHAFT
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                        CONCENTRIC NETWORK CORPORATION
                           10590 NORTH TANTAU AVENUE
                              CUPERTINO, CA 95014
                                (408) 342-2800
     (NAME, ADDRESS AND TELEPHONE NUMBER OF AGENT FOR SERVICE OF PROCESS)
 
                               ----------------

                                  COPIES TO:
           DAVID J. SEGRE                         THOMAS A. BEVILACQUA
         VALERIE SCHULTHIES                  BROBECK, PHLEGER & HARRISON LLP
            PAUL B. SHINN                         TWO EMBARCADERO PLACE
            VICTOR H. SIM                            2200 GENG ROAD
  WILSON SONSINI GOODRICH & ROSATI                 PALO ALTO, CA 94303
      PROFESSIONAL CORPORATION                       (415) 424-0160
         650 PAGE MILL ROAD
         PALO ALTO, CA 94304
           (415) 493-9300
 
                               ----------------

       APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC:
As soon as practicable after the effective date of this Registration Statement.

  If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, check the following box. [_]

  If this form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following
box and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering. [_]

  If this form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. [_]

  If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. [_]
                        
                     CALCULATION OF REGISTRATION FEE     
================================================================================
<TABLE>   
<CAPTION>
                                                       PROPOSED
                                          PROPOSED      MAXIMUM
 TITLE OF EACH CLASS OF     AMOUNT        MAXIMUM      AGGREGATE   AMOUNT OF
    SECURITIES TO BE         TO BE     OFFERING PRICE  OFFERING   REGISTRATION
       REGISTERED        REGISTERED(1)  PER SHARE(2)   PRICE(2)      FEE(3)
- ------------------------------------------------------------------------------
<S>                      <C>           <C>            <C>         <C>
Common Stock, $.001 par
 value.................    4,140,000       $12.00     $49,680,000   $15,055
</TABLE>    
===============================================================================
   
(1) Includes 540,000 shares which the Underwriters have the option to purchase
    solely to cover over-allotments, if any.     
   
(2) Estimated solely for the purpose of computing the amount of the
    registration fee. The estimate is made pursuant to Rule 457 of the
    Securities Act of 1933, as amended.     
   
(3) Represents the incremental registration fee for 1,140,000 shares of Common
    Stock at $12.00 per share. The Registrant paid the registration fee for
    the remaining 3,450,000 shares with its filing on May 16, 1997.     

                               ----------------

  The Registrant hereby amends this Registration Statement on such date or
dates as may be necessary to delay its effective date until the Registrant
shall file a further amendment which specifically states that this
Registration Statement shall thereafter become effective in accordance with
Section 8(a) of the Securities Act of 1933 or until the Registration Statement
shall become effective on such date as the Commission, acting pursuant to said
Section 8(a), may determine.
 
- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
<PAGE>
 
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+INFORMATION CONTAINED HEREIN IS SUBJECT TO COMPLETION OR AMENDMENT. A         +
+REGISTRATION STATEMENT RELATING TO THESE SECURITIES HAS BEEN FILED WITH THE   +
+SECURITIES AND EXCHANGE COMMISSION. THESE SECURITIES MAY NOT BE SOLD NOR MAY  +
+OFFERS TO BUY BE ACCEPTED PRIOR TO THE TIME THE REGISTRATION STATEMENT        +
+BECOMES EFFECTIVE. THIS PROSPECTUS SHALL NOT CONSTITUTE AN OFFER TO SELL OR   +
+THE SOLICITATION OF AN OFFER TO BUY NOR SHALL THERE BE ANY SALE OF THESE      +
+SECURITIES IN ANY STATE IN WHICH SUCH OFFER, SOLICITATION OR SALE WOULD BE    +
+UNLAWFUL PRIOR TO REGISTRATION OR QUALIFICATION UNDER THE SECURITIES LAWS OF  +
+ANY SUCH STATE.                                                               +
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
PROSPECTUS         SUBJECT TO COMPLETION, DATED JULY  , 1997
                                
                             3,600,000 SHARES     
                    [LOGO OF CONCENTRIC NETWORK CORPORATION]
 
                                  COMMON STOCK
 
                                  -----------
   
      All of the 3,600,000 shares of Common Stock offered hereby are being sold
by Concentric Network Corporation ("Concentric" or the "Company"). Prior to
this offering, there has been no public market for the Common Stock of the
Company. It is currently estimated that the initial public offering price will
be between $10.00 and $12.00 per share. See "Underwriting" for a discussion of
the factors to be considered in determining the initial public offering price.
The shares of Common Stock have been approved for quotation on the Nasdaq
National Market under the symbol "CNCX," subject to official notice of
issuance.     
 
  Williams Communications Group, Inc. and Bay Networks, Inc. have agreed to
purchase directly from the Company, in a private placement that will occur
concurrently with the closing of this offering, shares of Common Stock having
an aggregate purchase price of approximately $18.0 million. All of such shares
will be unregistered shares purchased at the per share Price to Public set
forth below. See "Direct Placements."
 
  THE COMMON STOCK OFFERED HEREBY INVOLVES A HIGH DEGREE OF RISK. SEE "RISK
FACTORS" BEGINNING ON PAGE 6.
 
                                  -----------
 
THESE SECURITIES  HAVE NOT BEEN APPROVED  OR DISAPPROVED BY THE  SECURITIES AND
 EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE SECURITIES
  AND EXCHANGE COMMISSION OR ANY  STATE SECURITIES COMMISSION PASSED UPON THE
  ACCURACY  OR  ADEQUACY  OF  THIS  PROSPECTUS.  ANY  REPRESENTATION  TO  THE
   CONTRARY IS A CRIMINAL OFFENSE.
 
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
<TABLE>
<CAPTION>
                                                       Underwriting
                                             Price to Discounts and  Proceeds to
                                              Public  Commissions(1) Company(2)
- --------------------------------------------------------------------------------
<S>                                          <C>      <C>            <C>
Per Share..................................    $           $            $
- --------------------------------------------------------------------------------
Total(3)...................................   $           $             $
</TABLE>
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
(1) For information regarding indemnification of Underwriters, see
    "Underwriting."
(2) Before deducting expenses of the offering payable by the Company, estimated
    at $1,000,000.
   
(3) The Company has granted the Underwriters an option, exercisable within 30
    days from the date hereof, to purchase up to 540,000 additional shares of
    Common Stock on the same terms set forth above, solely to cover over-
    allotments, if any. If such option is exercised in full, the total Price to
    Public will be $   , the Underwriting Discounts and Commissions will be
    $   , and Proceeds to Company will be $   . Including the Direct
    Placements, the total Proceeds to Company will be $   , or $    if the
    over-allotment is exercised in full. See "Underwriting."     
 
                                  -----------
 
  The shares of Common Stock offered by the Underwriters are subject to prior
sale, receipt and acceptance by them and subject to the right of the
Underwriters to reject any order in whole and in part and to certain other
conditions. It is expected that delivery of such shares will be made at the
offices of UBS Securities LLC, 299 Park Avenue, New York, New York on or about
      , 1997.
 
                                  -----------
 
UBS SECURITIES
                          UNTERBERG HARRIS            WHEAT FIRST BUTCHER SINGER
 
      , 1997
<PAGE>
 
                           THE CONCENTRIC NETWORK

                      [PICTURE OF GLOBE APPEARS HERE]

The Concentric network employs an advanced, geographically dispersed ATM and 
frame relay backbone, SuperPOPs in 14 major metropolitan areas and 132 
secondary and tertiary POPs in other cities, allowing dial up network access 
in the U.S. and Canada. The Company also offers network access to its customers
while they travel in Japan through a roaming agreement with NTT PC 
Communications, Inc. The Company is working to establish an international 
network based on Concentric's network technology and expertise and the 
telecommunications infrastructure of TMI Telemedia International, Ltd., a 
subsidiary of Telecom Italia SpA, to deliver a range of compatible network 
services worldwide.

                              CONCENTRICVIEW/TM
                  ConcentricView is a Web-based monitoring
              tool that provides up-to-date network information
                    to Concentric's corporate customers.

             [PICTURE OF GRAPHICAL USER INTERFACE APPEARS HERE]

       CERTAIN PERSONS PARTICIPATING IN THIS OFFERING MAY ENGAGE IN
     TRANSACTIONS WHICH STABILIZE, MAINTAIN OR OTHERWISE AFFECT THE
     PRICE OF THE COMMON STOCK OF THE COMPANY INCLUDING STABILIZING
     BIDS, SYNDICATE COVERING TRANSACTIONS OR THE IMPOSITION OF
     PENALTY BIDS. FOR A DISCUSSION OF THESE ACTIVITIES, SEE
     "UNDERWRITING."

                                       2
<PAGE>
 
                               PROSPECTUS SUMMARY
 
  The following summary should be read in conjunction with, and is qualified in
its entirety by, the more detailed information, including "Risk Factors" and
the Financial Statements and Notes thereto, appearing elsewhere in this
Prospectus. Except as otherwise noted or as the context otherwise requires, all
information in this Prospectus (i) gives effect to the conversion of all
outstanding shares of Preferred Stock into shares of Common Stock that will
occur automatically immediately prior to the closing of the offering, (ii)
gives effect to the reincorporation of the Company from Florida to Delaware
prior to the closing of the offering, (iii) gives effect to a one-for-15
reverse split of the Company's Common Stock and Preferred Stock and the
conversion of all shares of Class B Common Stock into shares of Common Stock,
which will occur prior to the closing of the offering, and (iv) assumes no
exercise of the Underwriters' over-allotment option. See "Description of
Capital Stock" and "Underwriting." In addition, all share numbers herein assume
that no stockholder receiving the Rescission Offer, which Rescission Offer will
be made as promptly as practicable following the closing of the offering,
exercises its right to rescind its purchase of shares of the Company's Common
Stock. See "Rescission Offers." Certain terms used in this Prospectus are
defined in the Glossary of Terms beginning on page G-1.
 
                                  THE COMPANY
 
  Concentric provides tailored, value-added Internet Protocol ("IP") based
network services for businesses and consumers. To provide these services, the
Company utilizes its low/fixed latency, high-throughput network, employing its
advanced network architecture and the Internet. Concentric's service offerings
for enterprises include virtual private networks ("VPNs"), dedicated access
facilities ("DAFs") and Web hosting services. These services enable enterprises
to take advantage of standard Internet tools such as browsers and high-
performance servers for customized data communications within an enterprise and
between an enterprise and its suppliers, partners and customers. These services
combine the cost advantages, nationwide access and standard protocols of public
networks with the customization, high performance, reliability and security of
private networks. Among the current enterprise customers are Acer America
Corporation, Inc., Intuit, Inc., WebTV Networks, Inc. and Ziff-Davis Publishing
Co. Concentric's service offerings for consumers and small office/home office
customers include local Internet dial-up access, Web hosting services and
online multiplayer gaming.
 
  Industry analysts expect the market size for both value-added IP data
networking services and Internet access to grow rapidly as businesses and
consumers increase their use of the Internet, intranets and privately managed
IP networks. The total market for these services is projected to grow from $1.2
billion in 1996 to approximately $22.7 billion in the year 2000, with
approximately $10.4 billion in the enterprise market segment and $12.3 billion
in the consumer market segment.
 
  The Concentric network employs an advanced, geographically dispersed ATM and
frame relay backbone, SuperPOPs in 14 major metropolitan areas and 132
secondary and tertiary POPs in other cities, allowing dial-up network access in
the U.S. and Canada. In addition, the Company can provide analog dial-up, frame
relay, fractional T-1, T-1 and DS3 access to the network. The Concentric
network is engineered and managed to provide superior quality of service,
balancing several key performance criteria. The Company provides guaranteed
levels of service for DAFs to enterprise customers, and targets performance
benchmarks for connection success rates, latency levels and throughput for all
of its service offerings. Concentric also believes that a major advantage of
its network architecture is its ability to perform adaptive call processing
("ACP"), which is designed to enable the tuning of network parameters and
traffic routing to meet the latency, throughput, security, and reliability
requirements of a specific customer or application on a call-by-call basis.
Concentric is currently deploying the ACP technology in its network and is
planning to commercially introduce these capabilities during the first half of
1998.
 
  In addition to strong network performance capabilities, the Company believes
that several factors distinguish its ability to provide value-added network
services. These factors include: (i) excellent service quality; (ii) rapid
development time and flexibility in meeting custom applications requirements;
(iii) responsive customer support and effective account management, available
24 hours per day, seven days per week through the Company's 142 customer
service personnel; and (iv) the Company's technical expertise in devising cost-
effective network solutions for customers.
 
                                       3
<PAGE>
 
 
  The Company's objective is to become the leading provider of value-added IP-
based network services worldwide. In order to achieve its goal, the Company is
implementing business strategies which capitalize on a number of opportunities
in the marketplace and a large and growing IP network access market. Key
strategies include: (i) rapidly providing cost-effective, tailored network
solutions; (ii) optimizing network utilization; (iii) employing leveraged
marketing through strategic partners; (iv) offering next generation network
services; and (v) deploying network services internationally.
 
  The Company aggressively pursues strategic alliances with a variety of
companies. Key partners currently include Bay Networks, Inc., Microsoft
Corporation, Netscape Communications, Inc. ("Netscape"), Williams
Communications Group, Inc., PictureTel Corporation, Racal-Datacom, Inc. and TMI
Telemedia International, Ltd., a subsidiary of Telecom Italia, SpA ("TMI"). The
Company is continuing to expand its value-added services, and plans to
introduce RemoteLink, a remote access service designed to help businesses
reduce the high costs of telecommunications charges and user support associated
with building, deploying and maintaining their own remote access WAN, in mid-
1997. In addition, Concentric is in early stage trials for videoconferencing
services and IP-based telephony services. The Company is also working with TMI
to establish an international network based on the Company's network technology
and expertise and TMI's global telecommunications infrastructure.
 
  The Company was incorporated in Florida in 1991 under the name Engineered
Video Concepts, Inc., changed its name to Concentric Research Corporation in
1992 and commenced network operations in 1994. In 1995, the Company changed its
name to Concentric Network Corporation. Unless the context otherwise requires,
"Concentric" and the "Company" refer to Concentric Network Corporation. The
address of the Company's principal executive offices is 10590 N. Tantau Avenue,
Cupertino, CA 95014, and its telephone number at that address is (408) 342-
2800.
 
  Concentric Network Corporation, The Concentric Network, Concentric
RemoteLink, ConcentricView, ConcentricHost, FlexChannel, FullChannel, Powered
by Concentric Network, and PremierConnect are among the trademarks of the
Company. This Prospectus contains other product names, trade names and
trademarks of the Company and of other organizations.
 
                                       4
<PAGE>
 
                                  THE OFFERING
 
<TABLE>   
 <C>                                                 <S>
 Common Stock offered by the Company................  3,600,000 shares(1)
 Common Stock to be outstanding after the offering.. 12,804,838 shares(2)
 Use of Proceeds.................................... For expansion of network
                                                     and data center
                                                     operations, to fund
                                                     operating losses and for
                                                     working capital and other
                                                     general corporate
                                                     purposes. In addition, the
                                                     Company expects to use a
                                                     portion of the proceeds to
                                                     fund the repurchase of
                                                     shares tendered in
                                                     connection with rescission
                                                     offers.
 Proposed Nasdaq National Market Symbol............. CNCX
</TABLE>    
- --------
(1) Excludes shares to be sold by the Company to certain strategic investors
    concurrent with the closing of this offering. See "Direct Placements."
   
(2) Includes an assumed 1,636,363 shares to be issued to certain strategic
    investors concurrent with the closing of this offering (assuming an initial
    public offering price of $11.00 per share) and excludes approximately
    151,789 shares to be repurchased by the Company from certain stockholders
    who are not officers, directors or affiliates of the Company at the per
    share Price to Public. See "Direct Placements." Excludes 3,460,447 shares
    issuable upon exercise of options and warrants outstanding at July 25, 1997
    at a weighted average exercise price of $9.87 per share. See "Description
    of Capital Stock--Warrants."     
 
                               DIRECT PLACEMENTS
 
  Williams Communications Group, Inc. and Bay Networks, Inc. have agreed to
purchase from the Company, in a private placement that will occur concurrently
with the closing of this offering, shares of Common Stock with an aggregate
purchase price of approximately $18.0 million (including approximately $3.0
million in cancellation of indebtedness). Such purchasers will pay to the
Company a per share amount equal to the Price to Public set forth on the cover
page of this Prospectus. See "Direct Placements" and "Certain Transactions--
Williams Transaction."
 
                            RECENT FINANCIAL RESULTS
 
  The Company's revenues, net loss and pro forma net loss per share for the
three months ended June 30, 1997 were $10.8 million, $12.9 million and $1.67,
respectively, as compared to revenues, net loss and pro forma net loss per
share for the three months ended June 30, 1996 of $2.5 million, $15.4 million
and $3.38, respectively. For the six months ended June 30, 1997, the Company's
revenues, net loss and pro forma net loss per share were $20.0 million, $27.6
million and $3.65, respectively, as compared to revenues, net loss and pro
forma net loss per share of $4.0 million, $25.8 million and $5.69 for the six
months ended June 30, 1996, respectively. The increase in revenues reflects
growth in revenue from the Company's broadened product offerings to its
enterprise customers and through the Company's leveraged marketing arrangements
with its strategic partners, as well as continued growth in revenues derived
from Internet access customers. During the three months ended June 30, 1997,
the Company recorded $970,000 of other income relating to the reversal of
reserves which were established for the Sattel litigation which has been
settled. Also during the three months ended June 30, 1997, the Company borrowed
$2.0 million from a stockholder and $3.0 million from a strategic partner which
will be repaid and which will convert into shares of Common Stock,
respectively, upon the closing of the offering made hereby and the Direct
Placement, and the Company acquired $7.8 million of equipment under capital
leases. As of June 30, 1997, the Company had a working capital deficit of $36.6
million. See "Use of Proceeds", "Direct Placements", "Certain Transactions--
Bridge Loans and Williams Transaction" and Note 10 of Notes to Financial
Statements.
 
                                       5
<PAGE>
 
                      SUMMARY FINANCIAL AND OPERATING DATA
                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
 
<TABLE>
<CAPTION>
                           PERIOD FROM
                           MAY 1, 1991                                        THREE MONTHS ENDED
                           (INCEPTION)       YEAR ENDED DECEMBER 31,               MARCH 31,
                             THROUGH    ------------------------------------  --------------------
                          DEC. 31, 1992  1993     1994      1995      1996      1996       1997
                          ------------- -------  -------  --------  --------  ---------  ---------
<S>                       <C>           <C>      <C>      <C>       <C>       <C>        <C>
STATEMENT OF OPERATIONS
 DATA:
Revenue.................      $ --      $    23  $   442  $  2,483  $ 15,648  $   1,533  $   9,154
Cost of revenue.........        --          130    2,891    16,168    47,945      7,256     15,744
Network equipment write-
 off(1) ................        --          --       --        --      8,321        --         --
Total operating
 expenses...............         28       1,114    1,784     7,602    22,503      4,196      7,021
                              -----     -------  -------  --------  --------  ---------  ---------
Loss from operations....        (28)     (1,221)  (4,233)  (21,287)  (63,121)    (9,919)   (13,611)
Net loss................      $ (28)    $(1,245) $(4,290) $(22,008) $(66,381) $ (10,380) $ (14,681)
                              =====     =======  =======  ========  ========  =========  =========
Pro forma net loss per
 share(2)...............                                            $ (11.92)            $   (1.98)
                                                                    ========             =========
Weighted average shares
 used in computing pro
 forma net loss per
 share(2)...............                                               5,567                 7,398
                                                                    ========             =========
</TABLE>
 
<TABLE>   
<CAPTION>
                                                          MARCH 31, 1997
                                                      ------------------------
                                                                  PRO FORMA
                                                       ACTUAL   AS ADJUSTED(3)
                                                      --------  --------------
<S>                                                   <C>       <C>
BALANCE SHEET DATA:
Working capital (deficit)............................ $(24,705)    $ 28,493
Property and equipment, net..........................   53,227       53,227
Total assets.........................................   61,438      114,636
Long-term debt and capital lease obligations, less
 current portion.....................................   35,349       35,349
Accumulated deficit.................................. (108,633)    (109,563)
Stockholders' equity (deficit).......................  (10,619)      41,649
</TABLE>    
 
<TABLE>
<CAPTION>
                                          THREE MONTHS ENDED
                            ---------------------------------------------------
                            MARCH 31,  JUNE 30,  SEPT. 30,  DEC. 31,  MARCH 31,
                              1996       1996      1996       1996      1997
                            ---------  --------  ---------  --------  ---------
<S>                         <C>        <C>       <C>        <C>       <C>
QUARTERLY STATEMENT OF
 OPERATIONS DATA:
Revenue...................  $  1,533   $  2,489  $  4,193   $  7,433  $  9,154
Cost of revenue...........     7,256     11,782    11,913     16,994    15,744
Network equipment write-
 off(1)...................       --         --        --       8,321       --
Total operating expenses..     4,196      5,475     5,464      7,368     7,021
                            --------   --------  --------   --------  --------
Loss from operations......    (9,919)   (14,768)  (13,184)   (25,250)  (13,611)
Net loss..................  $(10,380)  $(15,420) $(14,473)  $(26,108) $(14,681)
                            ========   ========  ========   ========  ========
</TABLE>
- --------
(1) See "Management's Discussion and Analysis of Financial Condition and
    Results of Operations" and Note 2 of Notes to Financial Statements.
(2) The pro forma net loss per share computation gives retroactive effect to
    the conversion of the outstanding Preferred Stock into Common Stock upon
    the closing of the offering. See Note 1 of Notes to Financial Statements
    for an explanation of the calculation of pro forma net loss per share.
   
(3) Adjusted to reflect the receipt by the Company of the estimated aggregate
    net proceeds of $53.2 million (including approximately $3.0 million in
    cancellation of indebtedness and the related write-off of approximately
    $930,000 in unamortized debt discount costs) from the sale of 3,600,000
    shares of Common Stock offered hereby and an assumed 1,636,363 shares
    offered in the Direct Placement at an assumed initial public offering price
    of $11.00 per share and excludes approximately 151,789 shares to be
    repurchased by the Company from certain stockholders who are not officers,
    directors or affiliates of the Company at the per share Price to Public.
    See "Use of Proceeds," "Direct Placements," "Certain Transactions" and Note
    10 of Notes to Financial Statements.     
 
 
                                       6
<PAGE>
 
                                 RISK FACTORS
 
  An investment in the shares of Common Stock offered hereby involves a high
degree of risk. Prospective investors should consider carefully the following
risk factors, in addition to the other information set forth in this
Prospectus, in connection with an investment in the Common Stock offered
hereby. The Prospectus contains forward-looking statements within the meaning
of Section 27A of the Securities Act of 1933, as amended (the "Securities
Act"), and Section 21E of the Securities Exchange Act of 1934, as amended (the
"Exchange Act"). Those statements appear in a number of places in this
Prospectus and include statements regarding the intent, belief or current
expectations of the Company or its directors or officers with respect to,
among other things: (i) trends affecting the Company's financial condition or
results of operation; and (ii) the Company's business and growth strategies.
Prospective investors are cautioned that any such forward-looking statements
are not guarantees of future performance and involve risks and uncertainties,
and that actual results may differ materially from those projected, expressed
or implied, in the forward-looking statements as a result of various factors.
The accompanying information contained in this Prospectus, including without
limitation the information set forth under the headings "Risk Factors,"
"Management's Discussion and Analysis of Financial Condition and Results of
Operations" and "Business," identifies important factors that could cause such
differences. Such forward-looking statements speak only as of the date of this
Prospectus, and the Company cautions potential investors not to place undue
reliance on such statements.
 
LIMITED OPERATING HISTORY; CONTINUING OPERATING LOSSES
 
  The Company was incorporated in 1991, commenced network operations in 1994
and completed initial deployment of its current network architecture and use
of an advanced ATM backbone network in late 1996. Accordingly, the Company has
a limited operating history upon which an evaluation of the Company and its
prospects can be based. In addition, a majority of the Company's senior
management team have been working together at the Company for less than two
years. The Company's prospects must be considered in light of the risks,
expenses and difficulties frequently encountered by companies in their early
stages of development, particularly companies in new and rapidly evolving
markets. To address these risks, the Company must, among other things, respond
to competitive developments, continue to attract, retain and motivate
qualified persons, and continue to upgrade its technologies and commercialize
its network services incorporating such technologies. There can be no
assurance that the Company will be successful in addressing such risks and the
failure to do so could have a material adverse effect on the Company's
business, financial condition and results of operations. The Company has
incurred net losses and experienced negative cash flow from operations since
inception and expects to continue to operate at a net loss and experience
negative cash flow at least through 1998, although the Company's ability to
achieve profitability and positive cash flow from operations is dependent upon
the Company's ability to substantially grow its revenue base and achieve other
operating efficiencies. The Company experienced net losses of approximately
$4.3 million, $22.0 million and $66.4 million for the years ended December 31,
1994, 1995 and 1996, respectively, and a net loss of $14.7 million for the
three months ended March 31, 1997. At March 31, 1997, the Company had an
accumulated deficit of approximately $108.6 million. There can be no assurance
that the Company will be able to achieve or sustain revenue growth,
profitability or positive cash flow on either a quarterly or an annual basis.
At December 31, 1996, the Company had approximately $37.0 million of gross
deferred tax assets comprised primarily of net operating loss carryforwards.
The Company believes that, based on a number of factors, the available
objective evidence creates sufficient uncertainty regarding the realizability
of the deferred tax assets such that a full valuation allowance has been
recorded. These factors include the Company's history of net losses since its
inception and the fact that the market in which the Company competes is
intensely competitive and characterized by rapidly changing technology. The
Company believes that, based on the current available evidence, it is more
likely than not that the Company will not generate taxable income through
1998, and possibly beyond, and accordingly will not realize the Company's
deferred tax assets through 1998 and possibly beyond. In addition, the
utilization of net operating losses may be subject to a substantial annual
limitation due to the "change in ownership" provisions of the Internal Revenue
Code of 1986 and similar state provisions. The Company will continue to assess
the realizability of the deferred tax assets based on actual and forecasted
operating results. See "Management's Discussion and Analysis of Financial
Condition and Results of Operations" and Note 8 of Notes to Financial
Statements.
 
FLUCTUATIONS IN OPERATING RESULTS
 
  The Company's operating results have fluctuated in the past and may in the
future fluctuate significantly depending upon a variety of factors, including
the timely deployment and implementation of expansion of the
 
                                       7
<PAGE>
 
Concentric network and new network architectures, the incurrence of related
capital costs, the receipt of new value-added network services and consumer
services subscriptions and the introduction of new services by the Company and
its competitors. Additional factors that may contribute to variability of
operating results include: the payment of statutory interest related to the
recission offer; the pricing and mix of services offered by the Company;
customer retention rate; market acceptance of new and enhanced versions of the
Company's services; changes in pricing policies by the Company's competitors;
the Company's ability to obtain sufficient supplies of sole- or limited-source
components; user demand for network and Internet access services; balancing of
network usage over a 24-hour period; and general access services. In response
to competitive pressures, the Company may take certain pricing or marketing
actions that could have a material adverse effect on the Company's business,
financial condition and results of operations. In addition, the Company's
expense levels are relatively fixed in the short term and are based, in part,
upon the Company's estimates of growth of its business. As a result,
variations in the timing and amounts of revenues could have a material adverse
effect on the Company's quarterly operating results. Due to the foregoing
factors, the Company believes that period-to-period comparisons of its
operating results are not necessarily meaningful and that such comparisons
cannot be relied upon as indicators of future performance. In the event that
the Company's operating results in any future period fall below the
expectations of securities analysts and investors, the trading price of the
Company's Common Stock would likely be materially and adversely affected. See
"Management's Discussion and Analysis of Financial Condition and Results of
Operations."
 
CUSTOMER CONCENTRATION
 
  The Company currently derives a substantial portion of its total revenue
from a single customer. For the year ended December 31, 1996 and the three
months ended March 31, 1997, revenue from WebTV Networks, Inc. ("WNI")
represented approximately 10.1% and 32.7%, respectively, of the Company's
revenue. The Company's current agreement to provide services to WNI expires on
December 1, 1997. After such date, the agreement continues in effect until
terminated by either party, which may occur at any time on or after September
30, 1997 upon one hundred twenty (120) days' notice. Although the Company
currently is negotiating a new agreement with WNI, there can be no assurance
such negotiations will be successfully concluded. While the Company expects
revenue from WNI to decrease as a percentage of revenue in future periods, the
Company believes that revenue derived from a limited number of current and
future customers may continue to represent a significant portion of its
revenue. As a result, the loss of one or more of the Company's major customers
could have a material adverse effect on the Company's business, financial
condition and results of operations. In addition, there can be no assurance
that revenue from customers that have accounted for significant revenue in
past periods, individually or as a group, will continue, or if continued, will
reach or exceed historical levels in any future period. See Note 1 of Notes to
Financial Statements.
 
MANAGEMENT OF POTENTIAL GROWTH AND EXPANSION
 
  As of December 31, 1995, the Company had 96 employees and 47 independent
contractors, and as of December 31, 1996, the Company had 246 employees and 46
independent contractors. As of March 31, 1997, the Company had 280 employees
and 48 independent contractors. The growth and expansion of the Company's
business and its service offerings have placed, and are expected to continue
to place, a significant strain on the Company's management, operational and
financial resources. The Company has recently expanded and upgraded its
network to use an ATM backbone. The Company plans to continue to substantially
expand its network in the future. There can be no assurance that the Company
will be able to add services at the rate or according to the schedule
presently planned by the Company. To manage its growth, the Company must,
among other things, (i) continue to implement and improve its operational,
financial and management information systems, including its billing, accounts
receivable and payable tracking, fixed assets and other financial management
systems; (ii) hire and train additional qualified personnel; and (iii)
continue to expand and upgrade its network infrastructure. Demands on the
Company's network infrastructure and technical support resources have grown
rapidly with the Company's expanding customer base, and the Company may in the
future experience difficulties meeting the demand for its access services and
technical support. There can be no assurance that the Company's technical
support or other resources will be sufficient to facilitate the Company's
growth. As the Company strives to increase total network utilization and to
optimize this utilization by targeting both business and consumer users to
balance the network's usage throughout a 24-hour
 
                                       8
<PAGE>
 
period, there will be additional demands on the Company's customer support,
sales and marketing resources. Any failure of the Company to manage its growth
effectively could have a material adverse effect on the Company's business,
financial condition and results of operations.
 
DEPENDENCE UPON NEW AND UNCERTAIN MARKETS
 
  The markets for tailored, value-added network services for businesses and
consumers offered by the Company, including Internet access, are in the early
stages of development. Since these markets are relatively new and because
current and future competitors are likely to introduce competing services or
products, it is difficult to predict the rate at which the market will grow,
if at all, or whether new or increased competition will result in market
saturation. Certain critical issues concerning commercial use of tailored
value-added services and Internet services, including security, reliability,
ease and cost of access and quality of service, remain unresolved and may
impact the growth of such services. If the markets for the services offered by
the Company, including Internet access, fail to grow, grow more slowly than
anticipated, or become saturated with competitors, the Company's business,
financial condition and results of operations would be materially adversely
affected. See "-- Competition," "-- Dependence upon New and Enhanced
Services," and "-- Risks of Technological Change and Evolving Industry
Standards."
 
DEPENDENCE UPON NEW AND ENHANCED SERVICES
 
  The Company has recently introduced new enterprise service offerings,
including the introduction of value-added, IP-based communication services to
enterprises. The failure of these services to gain market acceptance in a
timely manner or at all could have a material adverse effect on the business,
financial condition and results of operations of the Company. Introduction by
the Company of new or enhanced services with reliability, quality or
compatibility problems could significantly delay or hinder market acceptance
of such services, which could adversely affect the Company's ability to
attract new customers and subscribers. The Company's services may contain
undetected errors or defects when first introduced or as enhancements are
introduced. There can be no assurance that, despite testing by the Company or
its customers, errors will not be found in new services after commencement of
commercial deployment, resulting in additional development costs, loss of, or
delays in, market acceptance, diversion of technical and other resources from
the Company's other development efforts and the loss of credibility with the
Company's customers and subscribers. Any such event could have a material
adverse effect on the Company's business, financial condition and results of
operations. Additionally, if the Company is unable to achieve balanced network
utilization over a 24-hour period, the Concentric network could become
overburdened at certain periods during the day, which could adversely affect
the quality of service provided by the Company. Conversely, due to the high
fixed cost nature of Concentric's infrastructure, under-utilization of the
Concentric network during certain periods of the day could adversely affect
the Company's ability to provide cost-efficient services at other times. The
failure of the Company to achieve balanced network utilization, because of
either over- or under-utilization could have a material adverse effect on the
Company's business, financial condition and results of operations. See
"Business -- Services."
 
DEPENDENCE UPON SUPPLIERS; SOLE AND LIMITED SOURCES OF SUPPLY
 
  The Company relies on other companies to supply certain key components of
its network infrastructure, including telecommunications services and
networking equipment, which, in the quantities and quality demanded by the
Company, are available only from sole or limited sources. AT&T Corp. ("AT&T"),
MCI Telecommunications, Inc. ("MCI"), WorldCom, Inc. ("WorldCom") and PacWest
Telecomm, Inc. are the primary providers to the Company of data communications
facilities and capacity. AT&T is the sole provider of the frame relay backbone
of the Concentric network, and MCI is the sole provider of the ATM backbone of
the Concentric network. The Company is also dependent upon local exchange
carriers ("LECs") to provide telecommunications services to the Company and
its customers. The Company from time to time has experienced delays in
receiving telecommunications services, and there can be no assurance that the
Company will be able to obtain such services on the scale and within the time
frames required by the Company at an affordable cost, or at all. Any failure
to obtain such services on a timely basis at an affordable cost would have a
material adverse effect on the Company's business, financial condition and
results of operations.
 
                                       9
<PAGE>
 
  The routers, switches and modems the Company uses are supplied by Bay
Networks, Inc. through Racal-Datacom, Inc. ("Racal"). In addition, Racal acts
as a systems integrator. The servers primarily used in the Company's network
infrastructure are supplied solely by Sun Microsystems, Inc. The Company
purchases these components pursuant to purchase orders placed from time to
time, does not carry significant inventories of these components and has no
guaranteed supply arrangements for such components. The Company's suppliers
also sell products to the Company's competitors and may in the future
themselves become competitors of the Company. There can be no assurance that
the Company's suppliers will not enter into exclusive arrangements with the
Company's competitors or stop selling their products or components to the
Company at commercially reasonable prices or at all.
 
  Expansion of network infrastructures by the Company and others is placing,
and will continue to place, a significant demand on the Company's suppliers,
some of which have limited resources and production capacity. In addition,
certain of the Company's suppliers, in turn, rely on sole or limited sources
of supply of components included in their products. Failure of the Company's
suppliers to adjust to meet such increasing demand may prevent them from
continuing to supply components and products in the quantities and quality and
at the times required by the Company, or at all. The Company's inability to
obtain sufficient quantities of sole- or limited-source components or to
develop alternative sources if required could result in delays and increased
costs in expanding, and overburdening of, the Company's network
infrastructure, which would have a material adverse effect on the Company's
business, financial condition and results of operations.
 
  The Company also is dependent on its suppliers' ability to provide necessary
products and components that comply with various Internet and
telecommunications standards and that interoperate with products and
components from other vendors. Any failure of the Company's sole- or limited-
source suppliers to provide products or components that comply with Internet
standards or that interoperate with other products or components used by the
Company in its network infrastructure could have a material adverse effect on
the Company's business, financial condition and results of operations.
 
  Certain of the Company's suppliers, including the regional Bell operating
companies ("RBOCs") and other LECs, currently are subject to tariff controls
and other price constraints that in the future may be changed. In addition,
regulatory proposals are pending that may affect the prices charged by the
RBOCs and other LECs to the Company. Any such regulatory changes could result
in increased prices of products and services, which could have a material
adverse effect on the Company's business, financial condition and results of
operations. See "-- Dependence upon New and Enhanced Services" and "-- Risks
of Technological Change and Evolving Industry Standards."
 
DEPENDENCE UPON NETWORK INFRASTRUCTURE
 
  The Company's success will depend upon the capacity, reliability and
security of its network infrastructure. The Company currently derives a
significant portion of its revenue from customer subscriptions. The Company
expects that a substantial portion of its future revenues will be derived from
the provision of tailored value-added network services to its customers. The
Company must continue to expand and adapt its network infrastructure as the
number of users and the amount of information they wish to transfer increase,
and as customer requirements change. The Company's current projections of
utilization of the Concentric network require rapid expansion of the capacity
of the network to avoid capacity constraints that would adversely affect the
performance of the system. The expansion and adaptation of the Company's
network infrastructure will require substantial financial, operational and
management resources. There can be no assurance that the Company will be able
to expand or adapt its network infrastructure to meet additional demand or its
customers' changing requirements on a timely basis, at a commercially
reasonable cost, or at all. In addition, if demand for usage of the Concentric
network were to increase faster than projected or were to exceed the Company's
current forecasts, the network could experience capacity constraints, which
would adversely affect the performance of the system. Any failure of the
Company to expand its network infrastructure on a timely basis or adapt it to
either changing customer requirements or evolving industry standards, or
capacity constraints experienced by the Concentric network for any reason,
could have a material adverse effect on the Company's business, financial
condition and results of operations. Currently, the Company has a transit
agreement with networkMCI, Inc. to support the exchange of traffic between the
Concentric network and the Internet. The Company connects to the MCI Internet
via a DS3 (45 Mbps) link from its Bay City Data Center and another DS3 link
from its Cupertino Data
 
                                      10
<PAGE>
 
Center. The failure of the MCI Internet backbone, or either or both data
centers, or any other link in the delivery chain, and resulting interruption
in the Company's operations would have a material adverse effect on the
Company's business, financial condition and results of operations. See
"Business -- The Concentric Network."
 
COMPETITION
 
  The market for tailored value-added network services is extremely
competitive. There are no substantial barriers to entry, and the Company
expects that competition will intensify in the future. The Company believes
that its ability to compete successfully depends upon a number of factors,
including market presence; the capacity, reliability, low latency and security
of its network infrastructure; technical expertise and functionality,
performance and quality of services; customization; ease of access to and
navigation of the Internet; the pricing policies of its competitors and
suppliers; the variety of services; the timing of introductions of new
services by the Company and its competitors; customer support; the Company's
ability to support industry standards; and industry and general economic
trends.
 
  The Company's current and prospective competitors generally may be divided
into the following five groups: (i) telecommunications companies, such as
AT&T, MCI, Sprint, Inc., WorldCom, the RBOCs and various cable companies; (ii)
online services providers, such as America Online, Inc. ("America Online"),
CompuServe Incorporated ("CompuServe"), the Microsoft Network ("MSN") of
Microsoft Corporation ("Microsoft"), and Prodigy Services Company ("Prodigy");
(iii) Internet service providers ("ISPs"), such as BBN Corporation ("BBN"),
NETCOM On-Line Communications Services, Inc. ("NETCOM"), PSINet, Inc. ("PSI"),
and other national and regional providers; (iv) nonprofit or educational
Internet connectivity providers; and (v) Web server farms such as Internet
Direct and Exodus. Many of these competitors have greater market presence,
engineering and marketing capabilities, and financial, technological and
personnel resources than those available to the Company. As a result, they may
be able to develop and expand their communications and network infrastructures
more quickly, adapt more swiftly to new or emerging technologies and changes
in customer requirements, take advantage of acquisition and other
opportunities more readily, and devote greater resources to the marketing and
sale of their products and services than can the Company. In addition to the
companies named above, various organizations have entered into or are forming
joint ventures or consortiums to provide services similar to those of the
Company.
 
  The Company believes that new competitors, including large computer
hardware, software, media and other technology and telecommunications
companies, will enter the tailored value-added network services market,
resulting in even greater competition for the Company. Certain of such
telecommunications companies and online services providers are currently
offering or have announced plans to offer Internet or online services or to
expand their network services. Certain companies, including America Online,
BBN and PSI, have also obtained or expanded their Internet access products and
services as a result of acquisitions. Such acquisitions may permit the
Company's competitors to devote greater resources to the development and
marketing of new competitive products and services and the marketing of
existing competitive products and services. In addition, the ability of some
of the Company's competitors to bundle other services and products with
virtual private network services or Internet access services could place the
Company at a competitive disadvantage. Certain companies are also exploring
the possibility of providing or are currently providing high-speed data
services using alternative delivery methods such as over the cable television
infrastructure, through direct broadcast satellites and over wireless cable.
 
  The Company currently plans to apply for certificates of authority to become
a CLEC in selected states. To the extent the Company obtains such
authorizations and commences CLEC operations, it will compete with the
incumbent LEC and additional CLECS providing telecommunications services in
these markets. For all new entrants, including the Company, the market for
local exchange services is extremely competitive. Local telecommunications
services offered by the Company will compete principally with services offered
by the incumbent LEC serving that area. Incumbent LECs, such as the RBOCs,
currently dominate their local telephone markets. Such companies have
financial, managerial and technical resources that substantially exceed those
of the Company and have long-standing relationships with their customers.
While the 1996 Telecom Act provides increased business opportunities to CLECs,
it also allows incumbent LECs increased pricing flexibility for their
services. Increased price competition from incumbent LECs could have a
material adverse effect on the Company's CLEC operations and, in turn, on the
Company's results of operations and financial condition to the extent its CLEC
operations are a material portion of its
 
                                      11
<PAGE>
 
business. Furthermore, upon the satisfaction of certain regulatory conditions,
the RBOCs currently are expected to be able to offer long distance services in
their home markets in addition to local service, which would afford their
local customers "one-stop shopping" for telecommunications services. The
Company also expects to face increased competition in the provision of local
exchange services from other CLECs, cable television companies, electric
utilities, microwave carriers, wireless telephone system operators, AT&T, MCI,
Sprint, WorldCom and other long distance carriers who may choose to enter the
local exchange market by resale of incumbent LEC facilities.
 
  As a result of increased competition and vertical and horizontal integration
in the industry, the Company could encounter significant pricing pressure,
which in turn could result in significant reductions in the average selling
price of the Company's services. For example, certain of the Company's
competitors that are telecommunications companies may be able to provide
customers with reduced communications costs in connection with their Internet
access services or private network services, reducing the overall cost of
their solutions and significantly increasing price pressures on the Company.
There can be no assurance that the Company will be able to offset the effects
of any such price reductions with an increase in the number of its customers,
higher revenue from enhanced services, cost reductions or otherwise. In
addition, the Company believes that the Internet access and online services
businesses are likely to encounter consolidation in the near future, which
could result in increased price and other competition in these industries and,
potentially, the virtual private networks industry. Increased price or other
competition could result in erosion of the Company's market share and could
have a material adverse effect on the Company's business, financial condition
and results of operations. There can be no assurance that the Company will
have the financial resources, technical expertise or marketing and support
capabilities to continue to compete successfully. See "-- Management of
Potential Growth and Expansion" and "Business -- Competition."
 
DEPENDENCE UPON THIRD-PARTY MARKETING, DISTRIBUTION AND ENGINEERING
RELATIONSHIPS
 
  An important element of the Company's strategy is to develop relationships
with leading companies to enhance Concentric's engineering, marketing and
distribution efforts. The Company has OEM agreements with Netscape Corporation
("Netscape") and Microsoft pursuant to which the Company is entitled to
distribute and modify these companies' browsers. The customization of browsers
by the Company is an integral part of its current tailored VPN offerings. The
Netscape agreement expires in December 1998 and the Microsoft agreement
expires in March 1999. The Company has an agreement with Intuit, Inc.
("Intuit") for the development, operation and maintenance of a VPN that is the
integrated access, dial-up network and infrastructure used by purchasers of
Quicken, Turbo Tax and other Intuit software products to access the Quicken
Financial Network Website and upgrade to full Internet access. The Intuit
contract may be terminated at the election of Intuit upon six months prior
notice of an election to terminate. The Company relies on these relationships
for acquisition of consumer customers. The termination of or failure to renew
any of these agreements or the inability of the Company to enter into similar
relationships with others could have a material adverse effect on the
Company's business, financial condition and results of operation. The Company
has an outsourcing agreement with Critical Technologies Incorporated ("CTI"),
a subsidiary of Williams Communications Group, Inc., that enables the Company
to use CTI employees for the operational support of the Concentric network.
The Company's use of CTI employees and CTI engineering expertise were integral
to its development of the Concentric network and continue to be integral to
ongoing operation of the Company's network operations center. Pursuant to the
agreement with CTI, all of the CTI employees currently working for Concentric
will become employees of Concentric at the termination of the agreement in
December 2000. Termination of any of these agreements or the failure of the
Company to renew any of the agreements upon termination on terms acceptable to
the Company could result in a material adverse affect on the Company's
business, financial condition and results of operations. See "Business -- Key
Customer Applications."
 
RISKS OF TECHNOLOGICAL CHANGE AND EVOLVING INDUSTRY STANDARDS
 
  The markets for the Company's services are characterized by rapidly changing
technology, evolving industry standards, changes in customer needs, emerging
competition and frequent new product and service introductions. The Company's
future success will depend, in part, on its ability to effectively use leading
technologies; to continue to develop its technical expertise; to enhance its
current networking services; to develop new services that meet changing
customer needs; to advertise and market its services; and to influence and
respond to emerging industry standards and
 
                                      12
<PAGE>
 
other technological changes in a timely and cost-effective basis. There can be
no assurance that the Company will be successful in effectively using new
technologies, developing new services or enhancing its existing services on a
timely basis, or that such new technologies or enhancements will achieve
market acceptance. The Company's pursuit of necessary technological advances
may require substantial time and expense, and there can be no assurance that
the Company will succeed in adapting its network service business to alternate
access devices and conduits. An integral part of the Company's strategy is to
design its network in order to meet the requirements of emerging standards
such as 56.6 Kbps modems and applications such as IP-based interactive video
and voice conferencing communications. Failure of the Company, for
technological or other reasons, to develop and introduce new or enhanced
services that are compatible with industry standards and that satisfy customer
requirements would have a material adverse effect on the Company's business,
financial condition and results of operations. See "Business -- The Concentric
Network."
 
  The Company believes that its ability to compete successfully is also
dependent upon the continued compatibility and interoperability of its
services with products and architectures offered by various vendors. Although
the Company intends to support emerging standards in the market for Internet
access, there can be no assurance that industry standards will be established
or, if they become established, that the Company will be able to conform to
these new standards in a timely fashion and maintain a competitive position in
the market. Specifically, the Company's services rely on the continued
widespread commercial use of TCP/IP. Alternative open protocol and proprietary
protocol standards have been or are being developed. If any of these
alternative protocols become widely adopted, there may be a reduction in the
use of TCP/IP, which could render the Company's services obsolete and
unmarketable. Additionally, two of the leading modem manufacturers, Rockwell
and US Robotics, have proposed different, incompatible standards for 56.6 Kbps
modems. The Company currently plans to accommodate both standards to the
extent it can do so cost effectively. The failure of the Company to anticipate
the prevailing standard, or the failure of a common standard to emerge could
have a material adverse effect on the Company's business and results of
operations. In addition, there can be no assurance that services or
technologies developed by others will not render the Company's services or
technology uncompetitive or obsolete.
 
  The Company faces the risk of fundamental changes in the way Internet access
is delivered. Currently, Internet services are accessed primarily by computers
connected by telephone lines. Recently, several companies announced the
development and planned sale of cable television modems, wireless modems and
satellite modems to provide access to the Internet. Cable television,
satellite and wireless modems have the ability to transmit data at
substantially faster speeds than the modems the Company and its subscribers
currently use. In addition, wireless modems have the potential to reduce the
cost of network services. As the Internet becomes accessible through these
cable television, wireless and satellite modems and by screen-based
telephones, television or other consumer electronic devices, or subscriber
requirements change the way Internet access is provided, the Company will have
to develop new technology or modify its existing technology to accommodate
these developments. The Company's pursuit of these technological advances may
require substantial time and expense, and there can be no assurance that the
Company will succeed in adapting its Internet access business to alternate
access devices and conduits.
 
LEGAL PROCEEDINGS
 
  On April 22, 1997, a complaint was filed in the Los Angeles County,
California Superior Court against the Company and other unnamed defendants by
Sattel Communications LLC ("Sattel"). The complaint alleges claims for breach
of contract, breach of the covenant of good faith and fair dealing, unfair
business practices, fraud and negligent misrepresentation. Sattel claims that
the Company is in breach of an agreement to pay for up to $4.3 million of DSS
Switches from Sattel for use in the Company's network. The Complaint also
seeks unspecified consequential and punitive damages. On April 29, 1997,
Sattel served the Company with an Application for Writ of Attachment, seeking
to secure a lien on the Company's assets up to an amount of $3.6 million. At a
hearing held on June 25, 1997, the Court granted the writ. On July 11, 1997,
the Company entered into a Settlement Agreement and Mutual Release with Sattel
regarding the lawsuit (the "Settlement Agreement"). Pursuant to the Settlement
Agreement, the Company agreed to pay Sattel $4,400,000 for products that the
Company had purchased and received from Sattel, with such amount to be paid on
or before August 15, 1997. The Company also agreed to purchase, at the
election of Sattel, up to 25% of the Company's stock currently held by Sattel
on the day after the closing of the offering made
 
                                      13
<PAGE>
 
hereby at the initial Price to Public per share. As part of the settlement,
the Company and Sattel agreed to release each other from any claims they might
have against the other, and Sattel expressly released the Company from any
further obligation the Company might have to purchase additional equipment
from Sattel. The Company had previously reserved $5.8 million for the Sattel
litigation to account for the possible outcomes of the litigation.
 
  In late April and early May, 1997, three putative securities class action
complaints were filed in the United States District Court, Central District by
certain stockholders of Diana Corporation ("Diana"), the parent corporation of
Sattel, alleging securities fraud related to plaintiffs' purchase of shares of
Diana Common Stock in reliance upon allegedly misleading statements made by
defendants, Diana, Sattel and certain of their respective affiliates, officers
and directors. Concentric was named as a defendant in the complaint in
connection with certain statements made by Diana and officers of Diana related
to Concentric's purchase of network switching equipment from Diana's Sattel
subsidiary. The complaints do not appear to allege that Concentric made any
false or misleading statements. The plaintiffs seek unspecified compensatory
damages.
 
  While the ultimate outcome of such litigation is uncertain, the Company
believes it has meritorious defenses to the claims and intends to conduct
vigorous defenses. An unfavorable outcome in these matters could have a
material adverse effect on the Company's financial condition. In addition,
even if the ultimate outcomes are resolved in favor of the Company, the
defense of such litigation could entail considerable cost and the diversion of
efforts of management, either of which could have a material adverse effect on
the Company's results of operations. See "Business -- Legal Proceedings" and
Note 10 of Notes to Financial Statements.
 
RISK OF SYSTEM FAILURE
 
  As the Company expands its network and usage grows, increased stress will be
placed upon network hardware and traffic management systems. While the
Company's network has been designed with redundant backbone circuits to allow
traffic re-routing, there can be no assurance that the Company will not
experience failures relating to individual network points of presence ("POPs")
or even catastrophic failure of the entire network. Moreover, the Company's
operations are dependent upon its ability to protect its network
infrastructure against damage from fire, earthquakes, floods, mudslides, power
loss, telecommunications failures and similar events. A significant portion of
the Company's computer equipment, including critical equipment dedicated to
its Internet access services, is located at its facilities in Bay City,
Michigan, and Cupertino, California. In addition, the Company's modems and
routers that serve large areas of the United States are located in such
cities. The Company's network operations center, which manages the entire
network, is in St. Louis, Missouri. Despite precautions taken by the Company,
the occurrence of a natural disaster or other unanticipated problems at the
Company's network operations center, at its hubs (sites at which the Company
has located routers, switches and other computer equipment that make up the
backbone of the Company's network infrastructure) or at a number of the
Company's POPs has from time to time in the past caused, and in the future
could cause, interruptions in the services provided by the Company. In
addition, failure of the Company's telecommunications providers to provide the
data communications capacity in the time frame required by the Company as a
result of a natural disaster or operational disruption or for any other reason
could cause interruptions in the services provided by the Company. Any damage
or failure that causes interruptions in the Company's operations could have a
material adverse effect on the Company's business, financial condition and
results of operations. See "Business -- The Concentric Network."
 
SYSTEM SECURITY RISKS
 
  Despite the implementation of network security measures, the core of the
Company's network infrastructure is vulnerable to computer viruses, break-ins
and similar disruptive problems caused by its customers or Internet users.
Computer viruses, break-ins or other problems caused by third parties could
lead to interruptions, delays or cessation in service to the Company's
customers and subscribers. Furthermore, such inappropriate use of the network
by third parties could also potentially jeopardize the security of
confidential information stored in the computer systems of the Company and its
customers, which may result in liability to the Company and also may deter
potential subscribers. Although the Company intends to continue to implement
industry-standard security measures, such measures occasionally have been
circumvented in the past, and there can be no assurance that measures
implemented by the
 
                                      14
<PAGE>
 
Company will not be circumvented in the future. The costs and resources
required to eliminate computer viruses and alleviate other security problems
may result in interruptions, delays or cessation of service to the Company's
customers that could have a material adverse effect on the Company's business,
financial condition and results of operations. See "-- Management of Potential
Growth and Expansion," "-- Dependence upon New and Enhanced Services," "--
 Risks of Technological Change and Evolving Industry Standards," "Use of
Proceeds" and "Business -- Services."
 
DEPENDENCE UPON KEY PERSONNEL; NEED TO HIRE ADDITIONAL QUALIFIED PERSONNEL
 
  The Company's success depends to a significant degree upon the continued
contributions of its executive management team, including Henry R. Nothhaft,
the Company's President and Chief Executive Officer, and John K. Peters, the
Company's Executive Vice President and General Manager, Network Services
Division. The loss of the services of Messrs. Nothhaft or Peters could have a
material adverse effect on the Company. The Company does not have employment
agreements with any of its senior officers, including Messrs. Nothhaft or
Peters. Nor does the Company carry key man life insurance on the life of any
such persons. The Company's success will also depend upon the continued
service of the other members of its senior management team and technical,
marketing and sales personnel. The Company's employees may voluntarily
terminate their employment with the Company at any time, and competition for
qualified employees is intense. The Company's success also depends upon its
ability to attract and retain additional highly qualified management,
technical, sales and marketing and customer support personnel. The process of
locating such personnel with the combination of skills and attributes required
to carry out the Company's strategy is often lengthy. The loss of the services
of key personnel, or the inability to attract additional qualified personnel,
could have a material adverse effect upon the Company's results of operations,
development efforts and ability to complete the expansion of its network
infrastructure. Any such event could have a material adverse effect on the
Company's business, financial condition and results of operations. See "--
 Management of Potential Growth and Expansion" and "Management."
 
RISKS ASSOCIATED WITH INTERNATIONAL EXPANSION
 
  A key component of the Company's strategy is its planned expansion into
international markets. In particular, the Company has entered into an
agreement with TMI Telemedia International Ltd., a subsidiary of Telecom
Italia SpA ("TMI"), to establish an international network based on
Concentric's network technology and expertise and TMI's existing
telecommunications infrastructure to deliver a range of compatible network
services worldwide. If the companies are not able to successfully deploy
Concentric's technology over TMI's infrastructure, or if Concentric is
unsuccessful in transferring its knowledge to TMI employees, the Company's
international strategy may be delayed and the Company's business, results of
operation or financial condition could be materially adversely affected. To
date, the Company has only limited experience in working with TMI to develop
versions of its products and marketing and distributing its products
internationally. There can be no assurance that the Company will be able to
successfully market, sell and deliver its products in these markets. In
addition to the uncertainty as to the Company's ability to expand its
international presence, there are certain risks inherent in doing business on
an international level, such as unexpected changes in regulatory requirements,
export restrictions, export controls relating to encryption technology,
tariffs and other trade barriers, difficulties in staffing and managing
foreign operations, longer payment cycles, problems in collecting accounts
receivable, political instability, fluctuations in currency exchange rates,
seasonal reductions in business activity during the summer months in Europe
and certain other parts of the world and potentially adverse tax consequences
that could adversely impact the success of the Company's international
operations. There can be no assurance that one or more of such factors will
not have a material adverse effect on the Company's future international
operations and, consequently, on the Company's business, financial condition
and results of operations. See "Business -- Sales and Marketing."
 
FUTURE CAPITAL NEEDS; UNCERTAINTY OF ADDITIONAL FINANCING
 
  The Company currently anticipates that its available cash resources combined
with the net proceeds of the offering, the Direct Placements and existing
lease and credit facilities, and funds from operations will be sufficient to
meet its anticipated working capital and capital expenditure requirements for
the next 12 months. However, there can be no assurance that such resources
will be sufficient for its anticipated working capital and capital expenditure
 
                                      15
<PAGE>
 
requirements. The Company may need to raise additional funds through public or
private debt or equity financings in order to take advantage of unanticipated
opportunities, including more rapid international expansion or acquisitions of
complementary businesses or technologies, or to develop new products or
otherwise respond to unanticipated competitive pressures. The Company may also
raise additional funds through public or private debt or equity financings if
such financings become available on favorable terms. If additional funds are
raised through the issuance of equity securities, the percentage ownership of
then current stockholders of the Company may be reduced and such equity
securities may have rights, preferences or privileges senior to those of the
holders of the Company's Common Stock. If additional funds are raised through
the issuance of debt securities, such securities would have certain rights,
preferences and privileges senior to holders of Common Stock and the terms of
such debt could impose restrictions on the operations of the Company. There
can be no assurance that additional financing will be available on terms
favorable to the Company, or at all. If adequate funds are not available or
are not available on acceptable terms, the Company may not be able to take
advantage of unanticipated opportunities, develop new products or otherwise
respond to unanticipated competitive pressures. Such inability could have a
material adverse effect on the Company's business, results of operations and
financial condition. See "Use of Proceeds" and "Management's Discussion and
Analysis of Financial Condition and Results of Operations -- Liquidity and
Capital Resources."
 
RISKS ASSOCIATED WITH ACQUISITIONS
 
  The Company may seek to acquire assets or businesses complementary to its
operations, although no specific acquisitions are currently in negotiation or
planned. Any such future acquisitions would be accompanied by the risks
commonly encountered in acquisitions of companies. Such risks include, among
other things, the difficulty of assimilating the operations and personnel of
the acquired companies, the potential disruption of the Company's business,
the inability of the Company's management to maximize the financial and
strategic position of the Company by the incorporation of acquired technology
or business into the Company's service offerings, the difficulty of
maintaining uniform standards, controls, procedures and policies, the
potential loss of key employees of acquired companies, and the impairment of
relationships with employees and customers as a result of changes in
management. No assurance can be given that any acquisition by the Company will
or will not occur, that if an acquisition does occur it will not materially
and adversely affect the Company or that any such acquisition will be
successful in enhancing the Company's business. If the Company proceeds with
one or more significant acquisitions in which the consideration consists of
cash, a substantial portion of the Company's available cash, including
proceeds of this offering, could be used to consummate the acquisitions. If
the Company were to consummate one or more acquisitions in which the
consideration consisted of stock, stockholders of the Company could suffer
significant dilution of their interests in the Company. Many business
acquisitions must be accounted for as a purchase for financial reporting
purposes. Most of the businesses that might become attractive acquisition
candidates for the Company are likely to have significant goodwill and
intangible assets, and acquisition of these businesses, if accounted for as a
purchase, would typically result in substantial amortization of goodwill
charges to the Company.
 
GOVERNMENT REGULATION
 
  Value-Added Network and Internet Service Providers. The Federal
Communications Commission (the "FCC") currently does not regulate value-added
network software or computer equipment related services that transport data or
voice messages over telecommunication facilities. The Company provides value-
added IP-based network services, in part, through data transmissions over
public telephone lines. These transmissions are governed by regulatory
policies establishing charges and terms for wireline communications. Operators
of these types of value-added networks that provide access to regulated
transmission facilities only as part of a data services package currently are
excluded from regulations that applies to "telecommunications carrier" and as
such the Company is not currently subject to direct regulation by the FCC or
any other governmental agency, other than regulations applicable to businesses
generally. However, in the future the Company could become subject to
regulation by the FCC or another regulatory agency as a provider of basic
telecommunications services.
 
  Currently, the FCC is reviewing its regulatory positions and could seek to
impose common carrier regulation on the network transport and communications
facilities aspects of an enhanced or information service package. Further, the
FCC could conclude that the Company's protocol conversions, computer
processing, and interaction with
 
                                      16
<PAGE>
 
customer-supplied information are insufficient to afford the Company the
benefits of the enhanced or information service classification, and thereby
may seek to regulate some segments of the Company's activities as basic
telecommunications services. While state public utility commissions generally
have declined to regulate enhanced or information services, some states have
continued to regulate particular aspects of enhanced services in limited
circumstances, such as where they are provided by local exchange carriers
("LECs"). Moreover, the public service commissions of certain states continue
to review potential regulation of such services. There can be no assurance
that regulatory authorities of states within which Concentric makes its
Internet access, Intranet and VPN services available will not seek to regulate
aspects of these activities as telecommunications services. Changes in the
regulatory environment relating to the Internet connectivity market, including
regulatory changes that directly or indirectly affect telecommunications costs
or increase the likelihood or scope of competition from the RBOCs or other
telecommunications companies, could affect the prices at which the Company may
sell its services. The Company cannot predict the impact, if any, that future
regulation or regulatory changes may have on its business and there can be no
assurance that such future regulation or regulatory changes will not have a
material adverse effect on the Company's business, results of operations and
financial condition.
 
  Competitive Local Exchange Carriers. The Company may apply for certificates
of authority to become a CLEC in selected states. To the extent the Company
obtains such authorizations and commences CLEC operations, the
telecommunications services provided by such operations will be subject to
regulation by federal, state and local governmental agencies. At the federal
level, the FCC has jurisdiction over interstate telecommunications services.
State regulatory commissions exercise jurisdiction over intrastate services.
Additionally, municipalities and other local government agencies may regulate
limited aspects of the Company's business, such as use of rights-of-way.
Typically start-up telecommunications carriers are not as heavily regulated as
incumbent LECs. For example, under current regulations, the Company would not
be subject to price cap or rate of return regulation by the FCC. However, the
Telecommunications Act of 1996 (the "1996 Telecom Act") requires the FCC to
establish a subsidy mechanism for universal telephone service to which the
Company will be required to contribute based on its telecommunications
revenues and requires all LECs, including CLECs, to make services available
for resale by other carriers, provide nondiscriminatory access to rights-of-
way, offer reciprocal compensation for termination of local telecommunication
traffic and provide dialing parity and telephone number portability, and
ensure that their services are accessible to and usable by persons with
disabilities. The 1996 Telecom Act retains for individual states the authority
to impose their own regulations of local exchange services, including state
universal service subsidy programs, so long as this regulation is not
inconsistent with the requirements of the 1996 Telecom Act. The Company is
unable to predict the final form of such regulation and its potential impact
on the Company. In its provision of interstate, international and intrastate
services as a CLEC, the Company generally will be subject to tariff filing
requirements setting forth the terms, conditions and prices for services,
prior to offering telecommunications services. At the state level, the Company
will also be subject to state certification proceedings as a CLEC. These
certifications generally require a showing that the carrier has adequate
financial, managerial and technical resources to offer the proposed services
consistent with the public interest. Under some state statutes changes in the
ownership of the Company's outstanding voting securities also may trigger
additional state public utility commission approval. For example, in certain
jurisdictions an investor who acquires as little as ten percent or more of the
Company's voting securities may have to obtain prior approval of the
acquisition of such securities because such ownership might be deemed to
constitute an indirect controlling interest in the CLEC. While uncommon,
challenges to these tariffs and certificates by third parties could cause the
Company to incur substantial legal and administrative expenses. Many states
also have additional regulatory requirements such as minimum service quality
reporting and customer service requirements and uniform LEC accounting
requirements.
 
  Although the 1996 Telecom Act eliminates legal barriers to entry into the
CLEC market, no assurance can be given that changes in current or future
regulations adopted by the FCC or state regulators or other legislative or
judicial initiatives relating to the telecommunications industry would not
have a material adverse effect on the Company's ability to offer such
services. With the passage of the 1996 Telecom Act and the anticipated
increase in the level of competition faced by incumbent LECs, the FCC could
grant incumbent LECs substantial pricing flexibility with regard to interstate
access services. It is also anticipated that the prices incumbent LECs charge
for access services will be substantially reduced as a result of the FCC's
reform of the current access charge regime and
 
                                      17
<PAGE>
 
the adoption of universal service rules. Similarly, a number of states have
allowed incumbent LECs rate and tariff flexibility, particularly for services
deemed subject to competition. Such price competition could significantly and
adversely affect the Company's CLEC operations which could, in turn, adversely
affect the Company's results of operations and financial condition to the
extent its CLEC operations are a material portion of its business.
 
DEPENDENCE ON TECHNOLOGY; PROPRIETARY RIGHTS
 
  The Company's success and ability to compete is dependent in part upon its
technology, although the Company believes that its success is more dependent
upon its technical expertise than its proprietary rights. The Company
principally relies upon a combination of copyright, trademark and trade secret
laws and contractual restrictions to protect its proprietary technology. It
may be possible for a third party to copy or otherwise obtain and use the
Company's products or technology without authorization or to develop similar
technology independently, and there can be no assurance that such measures
have been, or will be, adequate to protect the Company's proprietary
technology or that the Company's competitors will not independently develop
technologies that are substantially equivalent or superior to the Company's
technology. The Company operates a material portion of its business over the
Internet, which is subject to a variety of risks. Such risks include but are
not limited to the substantial uncertainties that exist regarding the system
for assigning domain names and the status of private rules for resolution of
disputes regarding rights to domain names. There can be no assurance that the
Company will continue to be able to employ its current domain names in the
future or that the loss of rights to one or more domain names will not have a
material adverse effect on the Company's business and results of operations.
 
  Although the Company does not believe that it infringes the proprietary
rights of any third parties, there can be no assurance that third parties will
not assert such claims against the Company in the future or that such claims
will not be successful. The Company could incur substantial costs and
diversion of management resources with respect to the defense of any claims
relating to proprietary rights, which could have a material adverse effect on
the Company's business, financial condition and results of operations.
Furthermore, parties making such claims could secure a judgment awarding
substantial damages, as well as injunctive or other equitable relief that
could effectively block the Company's ability to license its products in the
United States or abroad. Such a judgment would have a material adverse effect
on the Company's business, financial condition and results of operations. In
addition, the Company is obligated under certain agreements to indemnify the
other party in connection with infringement by the Company of the proprietary
rights of third parties. In the event the Company is required to indemnify
parties under these agreements, it could have a material adverse effect on the
business, financial condition and results of operations of the Company. In the
event a claim relating to proprietary technology or information is asserted
against the Company, the Company may seek licenses to such intellectual
property. There can be no assurance, however, that licenses could be obtained
on commercially reasonable terms, if at all, or that the terms of any offered
licenses would be acceptable to the Company. The failure to obtain the
necessary licenses or other rights could have a material adverse effect on the
Company's business, financial condition and results of operations.
 
POTENTIAL LIABILITY FOR INFORMATION DISSEMINATED THROUGH NETWORK
 
  The law relating to the liability of online service providers, private
network operators and Internet service providers for information carried on or
disseminated through the facilities of their networks is currently unsettled.
Several lawsuits seeking a judgment of such liability are pending. In one case
brought against an Internet service provider, Religious Technology Center v.
Netcom On-Line Communication Services, Inc., the United States District Court
for the Northern District of California ruled in a preliminary phase that
under certain circumstances Internet service providers could be held liable
for copyright infringement. The case has not reached final judgment. Although
no claims have been asserted against the Company to date, there can be no
assurance that such claims will not be asserted in the future, or if asserted,
will not be successful. The Telecommunications Act of 1996 prohibits and
imposes criminal penalties and civil liability for using an interactive
computer service for transmitting certain types of information and content,
such as indecent or obscene communications. The indecency provision has been
declared unconstitutional by the United States District Court for the Eastern
District of Pennsylvania, which has issued a preliminary injunction against
its enforcement. The United States Supreme Court has recently heard arguments
with respect to the indecency provision and is expected to announce a decision
during the current term of Court. Numerous
 
                                      18
<PAGE>
 
states have adopted or are currently considering similar types of legislation.
The imposition upon the Company, Internet service providers or Web server
hosts of potential liability for materials carried on or disseminated through
their systems could require the Company to implement measures to reduce its
exposure to such liability, which may require the expenditure of substantial
resources or the discontinuation of certain product or service offerings.
Further, the costs incurred in defending against any such claims and potential
adverse outcomes of such claims could have a material adverse effect on the
Company's financial condition and results of operations. The Company believes
that it is currently unsettled whether the Telecommunications Act of 1996
prohibits and imposes liability for any services provided by the Company
should the content of information transmitted be subject to the statute.
 
SUBSTANTIAL CONTROL BY OFFICERS AND DIRECTORS AND THEIR AFFILIATES
   
  Following the offering and the Direct Placements, the Company's officers and
directors and their affiliates or the principal stockholders whom they
represent will beneficially own or control approximately 46.1% of the
outstanding shares of Common Stock (44.5% if the over-allotment option is
exercised in full). As a result, the Company's officers, directors and their
affiliates will have the ability to significantly influence the election of
the Company's Board of Directors and the outcome of corporate actions
requiring stockholder approval. See "Principal Stockholders."     
 
RESCISSION OFFERS
 
  The Company intends to commence approximately 30 days after the
effectiveness of the Offering made hereby, a rescission offer (the "Rescission
Offer") pursuant to a registration statement filed under the Securities Act of
1933, as amended (the "Act") and pursuant to the state securities laws of the
States of California, Florida, Illinois, Missouri, Kentucky, Texas, and
Wisconsin, covering convertible debentures and Common Stock sold to investors
which may have been sold in violation of the registration requirements of the
federal and state securities laws, which represent an aggregate of 105,828
shares as of June 30, 1997 (the "Rescission Stock"). Because of the frequency
and number of sales, including the number of persons who received offers and
who purchased shares, the private placement exemption under the Act may not
have been available for the Company's prior sales of the Rescission Stock. The
Company will offer to rescind such prior sales by repurchasing the Rescission
Stock at the price per share paid therefor (a range of $3.75 per share to
$30.00 per share) plus interest thereon at the statutory rate as the case may
be from the date of purchase by the purchaser to the expiration of the
Rescission Offer. The Rescission Offer will expire approximately 30 days after
the effectiveness of the registration statement with respect to the Rescission
Stock. Under such Rescission Offer, the Company would be required to make an
aggregate payment of approximately $1.4 million plus the aggregate amount of
interest thereon as described above, if all offerees accept the offer. The
Company currently expects to use a portion of the proceeds from this offering
to make such payments, if any are required. Offerees who do not accept the
Rescission Offer will, for purposes of applicable federal and state securities
laws, be deemed to hold registered shares under the Act which will be freely
tradeable in the public market as of the effective date of the registration
statement with respect to the Rescission Stock. The Act does not expressly
provide that a Rescission Offer will terminate a purchaser's right to rescind
a sale of stock which was not registered under the Act as required.
Accordingly, should the Rescission Offer be rejected by any or all offerees,
the Company may continue to be contingently liable under the Act for the
purchase price of Rescission Stock up to an aggregate amount of approximately
$1.4 million plus statutory interest of approximately $300,000.
 
  In addition, options issued pursuant to the Company's 1995 Stock Incentive
Plan for Employees and Consultants (the "1995 Plan") and nonplan options for
the purchase of Common Stock were issued to approximately 150 to 200 people in
California in 1995 and 1996 for which the Company was unable to rely on the
exemption provided by Section 25102(f) of the California Corporations Code. In
March 1996, the Company was denied a permit for these issuances by the
California Commissioner of Corporations as a result of the Company's having
had two classes of Common Stock with differing voting rights. In addition, a
smaller number of options were issued to optionees in other states, including
Michigan, Missouri, Virginia, Washington and Florida, for which the Company
may not have had available an exemption from qualification. Also, the November
17, 1995, grant of options for the purchase of 60,000 shares of Common Stock
to employees of Critical Technologies Incorporated was not qualified and may
not have had an exemption available under the Blue Sky laws of California. The
aforementioned options are potentially subject to rescission, and the Company
intends to include them in its planned Rescission Offer discussed above. Under
 
                                      19
<PAGE>
 
such Rescission Offer, the Company could be required to make an aggregate
payment of up to approximately $940,000 for such grants. The Company currently
expects to use a portion of the proceeds from this offering to make such
payments, if any are required.
 
  As of the date hereof, management is not aware of any claims for rescission
against the Company. While the Company will offer to rescind the securities
sales and grants, there are no assurances that the Company will not otherwise
be subject to possible penalties or fines relating to these issuances. The
Company believes the Rescission Offer will provide it with additional
meritorious defenses to any such future claims. See "Risk Factors--Rescission
Offers," "Use of Proceeds," "Shares Eligible for Future Sale" and Note 5 of
Notes to the Financial Statements.
 
ANTI-TAKEOVER PROVISIONS
 
  Certain provisions of Delaware law and the Company's Amended and Restated
Certificate of Incorporation and Bylaws could make it more difficult for a
third party to acquire, and could discourage a third party from attempting to
acquire, control of the Company. Certain of these provisions allow the Company
to issue Preferred Stock with rights senior to those of the Common Stock
without any further vote or action by the Stockholders, eliminate cumulative
voting and impose various procedural and other requirements that could make it
more difficult for Stockholders to effect certain corporate actions.
Additionally, the Company's Certificate of Incorporation provides for these
classes of directors, to be elected in a staggered basis. One class is elected
each year with each class serving a three year term, enabling management to
exercise significant control over the Company's affairs. Such charter
provisions could limit the price that certain investors might be willing to
pay in the future for shares of the Company's Common Stock or Preferred Stock
and may have the effect of delaying or preventing a change in control of the
Company. The issuance of Preferred Stock also could decrease the amount of
earnings and assets available for distribution to the holders of Common Stock
or could adversely affect the rights and powers, including voting rights, of
the holders of the Common Stock. See "Certain Transactions," "Description of
Capital Stock --Common Stock" and "-- Preferred Stock."
 
NO PRIOR PUBLIC MARKET; DETERMINATION OF PUBLIC OFFERING PRICE
 
  There has been no public market for the Company's Common Stock prior to the
offering. Although application has been made to the Nasdaq National Market for
listing of the Common Stock, there can be no assurance that an active trading
market will develop or be sustained or that the market price of the Common
Stock will not decline below the initial public offering price. The initial
public offering price will be determined through negotiations between the
Company and the Underwriters and may not be indicative of the market price for
the Common Stock following the offering. See "Underwriting" for a discussion
of the factors to be considered in determining the initial public offering
price. Even if an active trading market does develop, the market price of the
Common Stock following this offering may be highly volatile. Factors such as
variations in the Company's revenue, earnings and cash flow and announcements
of new service offerings, technological innovations or price reductions by the
Company, its competitors or providers of alternative services could cause the
market price of the Common Stock to fluctuate substantially. In addition, from
time to time the stock markets have experienced significant price and volume
fluctuations that particularly have affected companies in the technology and
telecommunications sectors and resulted in changes in the market price of the
stocks of many companies that have been unrelated or disproportionate to the
operating performance of those companies. Such broad market fluctuations, as
well as a shortfall in revenue earnings compared to securities analysts'
expectations, changes in analysts' recommendations or projections, and general
economic and market conditions may adversely affect the market price of the
Common Stock following this offering.
 
SHARES ELIGIBLE FOR FUTURE SALE; REGISTRATION RIGHTS
   
  Sales of substantial numbers of shares of Common Stock in the public market
could adversely affect the market price of the Common Stock and make it more
difficult for the Company to raise funds through equity offerings in the
future. A substantial number of outstanding shares of Common Stock and other
shares of Common Stock issuable upon exercise of outstanding stock options and
warrants will become available for resale in the public market at prescribed
times. Prior to this offering there has been no public market for the
Company's securities. Upon completion of the offering, in addition to the
shares sold in the offering, approximately 178,114 shares, which are not
subject to     
 
                                      20
<PAGE>
 
   
lock-up agreements, will be immediately eligible for resale in the public
market without restriction under the Act. The remaining 9,026,724 shares of
Common Stock held by existing stockholders are subject to lock-up agreements
with the Representatives. Of the shares of Common Stock subject to lock-up
agreements, approximately 7,600,193 shares may not be sold or transferred
until 360 days after the Effective date, approximately 1,295,627 shares may
not be sold or transferred until 180 days after the Effective Date and
approximately 126,105 shares may not be sold or transferred until 90 days
after the Effective Date. None of the shares subject to such lock-up
agreements may be sold or transferred during the applicable lock-up period
without the consent of the underwriters except for transfers pursuant to gifts
or certain partnership distributions and similar transfers in which the
transferee enters into a substantially similar lock-up agreement. Upon the
expiration of the lock-up agreements, all of such locked-up shares will become
eligible for sale either 360, 180 or 90 days, respectively, after the
Effective Date subject to the provisions of Rules 144(k), 144 or 701. UBS
Securities LLC may, in its sole discretion and at any time without notice,
release all or any portion of the securities subject to lock-up agreements.
The holders of approximately 7,296,253 shares of Common Stock are entitled to
certain registration rights with respect to such shares. In addition, the
Company intends to register the shares of Common Stock reserved for issuance
under the Company's 1995 Stock Incentive Option Plan, 1996 Stock Plan, 1997
Stock Plan and 1997 Employee Stock Purchase Plan following the date of this
Prospectus. See "Shares Eligible for Future Sale" and "Description of Capital
Stock -- Registration Rights."     
 
IMMEDIATE AND SUBSTANTIAL DILUTION
   
  Purchasers of the Common Stock offered hereby will suffer an immediate and
substantial dilution, in the amount of $7.49 per share, in the net tangible
book value per share of the Common Stock from the initial public offering
price. See "Dilution."     
 
                                      21
<PAGE>
 
                                USE OF PROCEEDS
   
  Assuming an initial public offering price of $11.00 per share, the net
proceeds from the sale of the shares of Common Stock offered hereby, after
deducting the underwriting discount and estimated offering expenses are
estimated to be approximately $35,828,000 (approximately $41,352,000 if the
Underwriters' over-allotment is exercised in full) and the proceeds from the
sale of Common Stock in the Direct Placements concurrently with the closing of
this offering are estimated to be approximately $17.4 million (including
approximately $3.0 million in cancellation of indebtedness).     
   
  The Company currently plans to use $3.0 million of the net proceeds from
this offering and the Direct Placements for capital expenditures associated
with expanding the Company's network and data center operations, $3.5 million
to pay license fees to strategic partners, $2.0 million to repay the
promissory notes issued to a stockholder of the Company in June 1997 and $4.4
million to settle the Sattel litigation. See "Certain Transactions--Bridge
Loans" and "Risk Factors--Legal Proceedings." The balance of the proceeds will
be used to fund operating losses and for working capital requirements or for
other general corporate purposes. Additionally, the Company currently expects
that a portion of the proceeds may also be used to fund the repurchase of
shares of the Company tendered in connection with the Company's Rescission
Offer in an amount up to $1.4 million plus approximately $200,000 of statutory
interest with respect to shares of Common Stock issued upon conversion of the
convertible debentures and an amount up to $940,000 with respect to the
options issued under the 1995 Plan. See "Rescission Offer." In addition,
approximately $1.7 million of the proceeds will be used to repurchase
approximately 151,789 shares of common stock from certain stockholders who are
not officers, directors or affiliates of the Company at the per share Price to
Public, and an additional $400,000 may be used to repurchase approximately
32,986 shares of common stock from certain stockholders who are not officers,
directors or affiliates of the Company at the per share Price to Public.
Proceeds from the offering also may be used for possible acquisitions of
businesses or technology that expand, complement or are otherwise related to
the Company's current services, although no specific acquisitions are
currently in negotiation or planned. Pending such uses, the proceeds will be
invested in short-term, investment grade, interest-bearing securities.     
 
                                DIVIDEND POLICY
 
  The Company has never declared or paid cash dividends on its capital stock.
The Company currently intends to retain all of its earnings, if any, for use
in its business and does not anticipate paying any cash dividends in the
foreseeable future.
 
                               DIRECT PLACEMENTS
 
  Williams Communications Group, Inc. and Bay Networks, Inc. have agreed to
purchase directly from the Company, in a private placement that will occur
concurrently with the closing of this offering (the "Direct Placements"),
shares of Common Stock with an aggregate purchase price of approximately $18.0
million (including approximately $3.0 million in cancellation of
indebtedness). All of such shares will be unregistered and will be purchased
at a per share amount equal to the per share Price to Public set forth on the
cover page of this Prospectus. At an assumed offering price of $11.00, such
purchasers would purchase an aggregate of 1,636,363 shares of Common Stock.
Such investors have agreed with the Company and with the Underwriters that
they will not sell or otherwise dispose of any Common Stock acquired in the
Direct Placements until at least one year after the closing of this offering.
See "Certain Transactions--Williams Transaction."
 
                                      22
<PAGE>
 
                                CAPITALIZATION
   
  The following table sets forth (i) the actual capitalization of the Company
derived from its financial statements as of March 31, 1997, (ii) such
capitalization presented to reflect on a pro forma basis the conversion of
Class B Common Stock and Preferred Stock into Common Stock (based on the
conversion ratios then in effect), and (iii) such pro forma capitalization as
adjusted to reflect the sale by the Company of (a) 3,600,000 shares of Common
Stock pursuant to this offering at an assumed public offering price of $11.00
per share and the receipt by the Company of the estimated net proceeds
therefrom, after deducting underwriting discounts and estimated offering
expenses and (b) an assumed 1,636,363 shares of Common Stock in the Direct
Placements at an assumed price of $11.00 per share (including approximately
$3.0 million in cancellation of indebtedness and the related write-off of
approximately $930,000 in unamortized debt discount costs). The capitalization
information set forth in the table below is qualified by the more detailed
Financial Statements and Notes thereto included elsewhere in this Prospectus
and should be read in conjunction with such Financial Statements and Notes.
    
<TABLE>   
<CAPTION>
                                                    MARCH 31, 1997
                                         --------------------------------------
                                                                   PRO FORMA
                                         ACTUAL(1)  PRO FORMA(1) AS ADJUSTED(2)
                                         ---------  ------------ --------------
                                                    (IN THOUSANDS)
<S>                                      <C>        <C>          <C>
Capital lease obligations, excluding
 current portion(3)..................... $  35,349   $  35,349     $  35,349
Stockholders' equity (deficit):
  Preferred Stock, $0.001 par value
   (7,333,333 shares authorized;
   4,901,231 shares issued and
   outstanding actual; 10,000,000 shares
   authorized, none outstanding pro
   forma and pro forma as adjusted).....    96,323         --            --
  Common Stock, $0.001 par value
   (13,343,333 shares authorized;
   1,395,788 shares issued and
   outstanding actual; 100,000,000
   shares authorized pro forma and pro
   forma as adjusted; 6,410,836 shares
   outstanding pro forma; 11,647,199
   shares outstanding pro forma as
   adjusted)............................     1,958      98,281       151,479
  Deferred compensation.................      (267)       (267)         (267)
  Accumulated deficit...................  (108,633)   (108,633)     (109,563)
                                         ---------   ---------     ---------
  Total stockholders' equity (deficit)..   (10,619)    (10,619)       41,649
                                         ---------   ---------     ---------
Total capitalization.................... $  24,730   $  24,730     $  76,998
                                         =========   =========     =========
</TABLE>    
- --------
(1) Excludes 483,749 shares of Common Stock issued after March 31, 1997 and
    3,460,447 shares issuable upon exercise of options and warrants
    outstanding at July 25, 1997 at a weighted average exercise price of $9.87
    per share. In addition, the foregoing tables exclude the Common Stock
    subject to rescission. Therefore such shares are excluded from the number
    of shares outstanding and the purchase price thereof is excluded from
    total consideration paid for shares. See "Description of Capital Stock--
    Warrants."
   
(2) Excludes approximately 151,789 shares to be repurchased by the Company
    from certain stockholders who are not officers, directors or affiliates of
    the Company at the per share Price to Public. See "Direct Placements."
        
(3) See Note 3 of Notes to Financial Statements.
 
                                      23
<PAGE>
 
                                   DILUTION
   
  The net tangible book value of the Company as of March 31, 1997 was
approximately $(12,322,000), or $(1.92) per share of Common Stock. Net
tangible book value per share is equal to the Company's total tangible assets
less its total liabilities, divided by the number of shares of Common Stock
outstanding after giving pro forma effect to the conversion into Common Stock
of all Class B Common Stock and all outstanding Preferred Stock (based on the
conversion ratios then in effect). After giving effect to the sale of
3,600,000 shares of Common Stock offered hereby and an assumed 1,636,363
shares offered in the Direct Placements at an assumed public offering price of
$11.00 per share and the receipt by the Company of the estimated net proceeds
therefrom, after deducting underwriting discounts and estimated offering
expenses, but excludes the repurchase by the Company of 151,789 shares from
certain stockholders who are not officers, directors or affiliates of the
Company at the per share Price to Public, the net tangible book value of the
Company as of March 31, 1997 would have been approximately $40,876,000, or
$3.51 per share. This represents an immediate increase in net tangible book
value of $5.43 per share to existing stockholders and an immediate dilution of
$7.49 per share to new investors. The following table illustrates this per
share dilution:     
 
<TABLE>   
   <S>                                                           <C>     <C>
   Assumed public offering price per share......................         $11.00
                                                                         ------
     Net tangible book value per share before the offering and
      Direct Placements(1)...................................... $(1.92)
                                                                 ------
     Increase per share attributable to new investors in the
      offering..................................................   5.43
                                                                 ------
   Net tangible book value per share after the offering and
    Direct Placements...........................................           3.51
                                                                         ------
   Dilution per share to new investors..........................         $ 7.49
                                                                         ======
</TABLE>    
 
  The following table summarizes as of March 31, 1997, the number of shares of
Common Stock purchased from the Company, the total consideration paid to the
Company and the average price per share paid by existing stockholders, by
investors participating in the Direct Placements and by the investors
purchasing shares of Common Stock in this offering (before deducting
underwriting discounts and estimated offering expenses):
 
<TABLE>   
<CAPTION>
                               SHARES PURCHASED  TOTAL CONSIDERATION   AVERAGE
                              ------------------ -------------------- PRICE PER
                                NUMBER   PERCENT    AMOUNT    PERCENT   SHARE
                              ---------- ------- ------------ ------- ---------
<S>                           <C>        <C>     <C>          <C>     <C>
Existing stockholders(1).....  6,410,836   55.0% $ 98,281,000   63.1%  $15.33
Direct placements............  1,636,363   14.1    18,000,000   11.5    11.00
Investors in the offering....  3,600,000   30.9    39,600,000   25.4    11.00
                              ----------  -----  ------------  -----
  Total...................... 11,647,199  100.0% $155,881,000  100.0%
                              ==========  =====  ============  =====
</TABLE>    
- --------
(1) Adjusted to give effect to the conversion of all outstanding shares of
    Class B Common Stock and Preferred Stock into Common Stock.
 
  The foregoing tables (i) do not give effect to the issuance of 483,749
shares of Common Stock after March 31, 1997 pursuant to the exercise of
options and warrants, (ii) assume no exercise of the Underwriters' over-
allotment option, and (iii) exclude 3,460,447 shares that were issuable upon
exercise of options and warrants outstanding at July 25, 1997 at a weighted
average exercise price of $9.87 per share. See "Description of Capital Stock--
Warrants." To the extent of such new issuances and to the extent that
outstanding options and warrants are exercised in the future, there will be
further dilution to new investors. In addition, the foregoing tables exclude
the Common Stock subject to rescission. Therefore such shares are excluded
from the number of shares outstanding, the purchase price thereof is treated
as a liability in calculating net tangible value and such amount is deducted
from total consideration paid for shares.
 
                                      24
<PAGE>
 
                            SELECTED FINANCIAL DATA
 
  The following selected financial data should be read in conjunction with the
Financial Statements and related notes thereto and "Management's Discussion
and Analysis of Financial Condition and Results of Operations" appearing
elsewhere herein. The selected financial data for the three years ended
December 31, 1996 are derived from financial statements of the Company which
have been audited by Ernst & Young LLP, independent auditors and included
elsewhere herein. The selected financial data for the period from May 1, 1991
(inception) through December 31, 1992 and for the year ended December 31, 1993
and for the three-month periods ended March 31, 1996 and March 31, 1997 are
derived from unaudited financial statements. The unaudited financial
statements include all adjustments, consisting of normal recurring accruals,
which the Company considers necessary for a fair presentation of the financial
position and results of operations for these periods. The operating results
for the three months ended March 31, 1997 are not necessarily indicative of
the results to be expected for any future period. See "Management's Discussion
and Analysis of Financial Condition and Results of Operations."
 
<TABLE>
<CAPTION>
                          PERIOD FROM
                          MAY 1, 1991
                          (INCEPTION)                                          THREE MONTHS
                            THROUGH         YEAR ENDED DECEMBER 31,           ENDED MARCH 31,
                          DECEMBER 31, ------------------------------------  ------------------
                              1992      1993     1994      1995      1996      1996      1997
                          ------------ -------  -------  --------  --------  --------  --------
                                        (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                       <C>          <C>      <C>      <C>       <C>       <C>       <C>
STATEMENT OF OPERATIONS                
 DATA:                                 
Revenue.................     $ --      $    23  $   442  $  2,483  $ 15,648  $  1,533  $  9,154
Costs and operating                    
 expenses                              
 Cost of revenue........       --          130    2,891    16,168    47,945     7,256    15,744
 Network equipment                     
  write-off(1)..........       --          --       --        --      8,321       --        --
 Development............       --          349      534       837     2,449       340     1,025
 Marketing and sales....       --          131      639     3,899    16,609     3,120     4,936
 General and                           
  administrative........        28         634      611     2,866     3,445       736     1,060
                             -----     -------  -------  --------  --------  --------  --------
 Total costs and                       
  operating expenses....        28       1,244    4,675    23,770    78,769    11,452    22,765
                             -----     -------  -------  --------  --------  --------  --------
Loss from operations....       (28)     (1,221)  (4,233)  (21,287)  (63,121)   (9,919)  (13,611)
Net interest expense....       --           24       57       721     3,260       461     1,070
                             -----     -------  -------  --------  --------  --------  --------
Net loss................     $ (28)    $(1,245) $(4,290) $(22,008) $(66,381) $(10,380) $(14,681)
                             =====     =======  =======  ========  ========  ========  ========
Pro forma net loss per                 
 share(2)...............                                           $ (11.92)           $  (1.98)
                                                                   ========            ========
Weighted average shares                
 used in computing pro                 
 forma net loss per                    
 share(2)...............                                              5,567               7,398
                                                                   ========            ========
</TABLE>
 
<TABLE>
<CAPTION>
                                       DECEMBER 31,
                          -----------------------------------------  MARCH 31,
                          1992    1993     1994     1995     1996      1997
                          -----  -------  -------  ------- --------  ---------
                                           (IN THOUSANDS)
<S>                       <C>    <C>      <C>      <C>     <C>       <C>
BALANCE SHEET DATA:
Working capital
 (deficit)............... $ --   $  (603) $(1,046) $ 8,992 $(10,868) $(24,705)
Property and equipment,
 net.....................   --       675    1,303   16,289   47,927    53,227
Total assets.............   --       783    1,798   37,235   70,722    61,438
Long-term debt and
 capital lease
 obligations, less
 current portion.........   --       491      --    10,977   30,551    35,349
Convertible debentures...            760    1,648       70      --        --
Common stock subject to
 rescission..............   --       --     2,812    5,080    5,150     5,150
Common and preferred
 stock...................    28      101    1,360   37,334   97,065    98,281
Deferred compensation....   --       --       --       --      (188)     (267)
Stockholders' equity
 (deficit)...............   (28)  (1,172)  (4,203)   9,763    2,925   (10,619)
</TABLE>
- --------
(1) See Management's Discussion and Analysis of Financial Condition and
    Results of Operations and Note 2 of Notes to Financial Statements.
(2) The pro forma net loss per share computation gives retroactive effect to
    the conversion of outstanding Preferred Stock into Common Stock upon
    closing of the offering. See Note 1 of Notes to the Financial Statements
    for an explanation of the calculation of pro forma net loss per share.
 
                                      25
<PAGE>
 
                    MANAGEMENT'S DISCUSSION AND ANALYSIS OF
                 FINANCIAL CONDITION AND RESULTS OF OPERATIONS
 
  The following discussion should be read in conjunction with financial
statements and related notes included elsewhere in this Prospectus. The
results shown herein are not necessarily indicative of the results to be
expected in any future periods. This discussion contains forward-looking
statements based on current expectations which involve risks and
uncertainties. Actual results and the timing of certain events may differ
significantly from those projected in such forward-looking statements due to a
number of factors, including those set forth in the section entitled "Risk
Factors" and elsewhere in this Prospectus.
 
OVERVIEW
 
  Concentric was founded in 1991. From 1991 to mid-1993, the Company conducted
development and network services planning activities and realized no revenues.
Initially, the Company was focused on providing consumers with direct dial-up
connectivity to bulletin board services. On-line gaming and entertainment
services for consumers were commenced in July 1993 through the utilization of
a third party network infrastructure. The Company commenced operation of its
own network in late 1994.
 
  In May 1995, new management led by Henry R. Nothhaft redefined and broadened
the Company's strategy to provide a range of Internet and tailored, value-
added IP-based network services to consumers and businesses.
 
  The Company's revenue prior to 1996 has been primarily generated from
providing Internet access to consumers. The Company's current focus is on
developing and deploying VPNs and providing network access and Web hosting
services for enterprise customers. Contracts with enterprise customers
typically have a term ranging from one to three years. The Company expects
enterprise-related revenue to represent an increasing portion of total revenue
in future periods. The foregoing expectation is a forward-looking statement
that involves risks and uncertainties, and actual results could vary as a
result of a number of factors including the Company's operating results, the
results and timing of the Company's launch of new products and services,
governmental or regulatory changes, the ability of the Company to meet product
and project demands, the success of the Company's marketing efforts,
competition and acquisitions of complementary businesses, technologies or
products.
 
  The Company has incurred net losses and experienced negative cash flow from
operations since inception and expects to continue to operate at a net loss
and experience negative cash flow at least through 1998, although the
Company's ability to achieve profitability and positive cash flow from
operations is dependent upon the Company's ability to substantially grow its
revenue base and achieve other operating efficiencies. The Company experienced
net losses of approximately $4.3 million, $22.0 million and $66.4 million for
the years ended December 31, 1994, 1995 and 1996, respectively and $14.7
million for the quarter ended March 31, 1997. At March 31, 1997, the Company
had an accumulated deficit of approximately $108.6 million. There can be no
assurance that the Company will be able to sustain revenue growth or to
achieve profitability or positive cash flow on either a quarterly or an annual
basis. At December 31, 1996, the Company had approximately $37.0 million of
gross deferred tax assets comprised primarily of net operating loss
carryforwards. The Company believes that, based on a number of factors, the
available objective evidence creates sufficient uncertainty regarding the
realizability of the deferred tax assets such that a full valuation allowance
has been recorded. These factors include the Company's history of net losses
since its inception and the fact that the market in which the Company competes
is intensely competitive and characterized by rapidly changing technology. The
Company believes that, based on the current available evidence, it is more
likely than not that the Company will not generate taxable income through
1998, and possibly beyond, and accordingly will not realize the Company's
deferred tax assets through 1998, and possibly beyond. In addition, the
utilization of net operating losses maybe subject to a substantial annual
limitation due to the "change in ownership" provisions of the Internal Revenue
Code of 1986 and similar state provisions. The Company will continue to assess
the realizability of the deferred tax assets based on actual and forecasted
operating results. See Note 8 of Notes to Financial Statements.
 
 
                                      26
<PAGE>
 
RECENT FINANCIAL RESULTS
 
  The Company's revenues, net loss and pro forma net loss per share for the
three months ended June 30, 1997 were $10.8 million, $12.9 million and $1.67,
respectively, as compared to revenues, net loss and pro forma net loss per
share for the three months ended June 30, 1996 of $2.5 million, $15.4 million
and $3.38, respectively. For the six months ended June 30, 1997, the Company's
revenues, net loss and pro forma net loss per share were $20.0 million, $27.6
million and $3.65, respectively, as compared to revenues, net loss and pro
forma net loss per share of $4.0 million, $25.8 million and $5.69 for the six
months ended June 30, 1996, respectively. The increase in revenues reflects
growth in revenue from the Company's broadened product offerings to its
enterprise customers and through the Company's leveraged marketing
arrangements with its strategic partners, as well as continued growth in
revenues derived from Internet access customers. During the three months ended
June 30, 1997, the Company recorded $970,000 of other income relating to the
reversal of reserves which were established for the Sattel litigation which
has been settled. Also during the three months ended June 30, 1997, the
Company borrowed $2.0 million from a stockholder and $3.0 million from a
strategic partner which will be repaid and which will convert into shares of
Common Stock, respectively, upon the closing of the offering made hereby and
the Direct Placement and the Company acquired $7.8 million of equipment under
capital leases. As of June 30, 1997, the Company had a working capital deficit
of $36.6 million. See "Use of Proceeds", "Direct Placements", "Certain
Transactions--Bridge Loans and Williams Transaction" and Note 10 of Notes to
Financial Statements.
 
RESULTS OF OPERATIONS
 
 THREE MONTHS ENDED MARCH 31, 1997 COMPARED TO THREE MONTHS ENDED MARCH 31,
1996
 
  Revenue. Revenue totaled approximately $9.2 million for the three months
ended March 31, 1997, a $7.7 million increase over revenue of approximately
$1.5 million for the three months ended March 31, 1996. This increased revenue
reflects growth in revenue from the Company's broadened product offerings to
its enterprise customers and through the Company's leveraged marketing
arrangements with its strategic partners, as well as continued growth in
revenue derived from Internet access customers. For the three months ended
March 31, 1997, revenue from WebTV Networks, Inc. ("WNI") accounted for 32.7%
of the Company's revenue. No other customer accounted for more than 10% of the
Company's revenue during the period. The Company expects revenue from WNI to
decrease both in absolute amounts and as a percentage of revenue.
 
  Cost of Revenue. Cost of revenue consists primarily of personnel costs to
maintain and operate the Company's network, access charges from local exchange
carriers, backbone and Internet access costs, depreciation of network
equipment and amortization of related assets. Cost of revenue for the three
month period ended March 31, 1997 was approximately $15.7 million, an increase
of $8.4 million from cost of revenue of $7.3 million in the first quarter of
1996. This increase is attributable to the overall growth in the size of the
network. As a percentage of revenue, such costs declined to 172.0% of revenue
in the three months ended March 31, 1997 from 473.3% of revenue in the year
earlier period, due to increased network utilization associated with the
Company's revenue growth and lower per port costs of the Company's SuperPOP
network architecture deployed in the second half of 1996. The Company expects
its cost of revenue to continue to increase in dollar amount, while declining
as a percentage of revenue as the Company expands its customer base.
 
  Development. Development expense consists primarily of personnel and
equipment related expenses associated with the development of products and
services of the Company. Development expense was approximately $1.0 million
and $300,000 for the three months ended March 31, 1997 and 1996, respectively.
This higher level of development expense reflects an overall increase in
personnel to develop new product offerings and to manage the overall growth in
the network. Development expense as a percentage of revenue declined to 11.2%
for the three months ended March 31, 1997 from 22.2% in the year earlier
period as a result of the Company's increased revenue. The Company expects its
development spending to continue to increase in dollar amount, but to decline
as a percentage of revenue.
 
  Marketing and Sales. Marketing and sales expense consists primarily of
personnel expenses, including salary and commissions, costs of marketing
programs and the cost of 800 number circuits utilized by the Company for
customer
 
                                      27
<PAGE>
 
support functions. Marketing and sales expense was approximately $4.9 million
and $3.1 million for the three months ended March 31, 1997 and 1996,
respectively. The $1.8 million increase in 1997 reflects a substantial
investment in the customer support, marketing and sales organizations
necessary to support the Company's expanded customer base. This increase also
reflects a growth in subscriber acquisition costs, related to both increased
direct marketing efforts as well as commissions paid to distribution partners.
Additionally, the increase reflects the ramp-up of marketing efforts related
to the introduction of enterprise products and services. Marketing and sales
expense as a percentage of revenue declined to 53.9% for the three months
ended March 31, 1997 from 203.5% in the year earlier period as a result of the
Company's increased revenue. The Company expects marketing and sales
expenditures to continue to increase in dollar amount, but to decline as a
percentage of revenue.
 
  General and Administrative. General and administrative expense consists
primarily of personnel expense and professional fees. General and
administrative expense was approximately $1.1 million and $700,000 for the
three months ended March 31, 1997 and 1996, respectively. This higher level of
expense reflects an increase in personnel and professional fees necessary to
manage the financial, legal and administrative aspects of the business.
General and administrative expense as a percentage of revenue declined to
11.6% for the three months ended March 31, 1997 from 48.0% in the year earlier
period as a result of the Company's increased revenue. The Company expects
general and administrative expense to increase in dollar amount, reflecting
its growth in operations and costs associated with being a publicly held
entity, but to decline as a percentage of revenue.
 
  Net Interest Expense. Net interest expense was approximately $1.1 million
and $500,000 for the first quarter of 1997 and 1996, respectively. The
increase is primarily due to an increase of $31.6 million in principal amount
of capitalized lease obligations from March 31, 1996 to March 31, 1997.
 
  Net Loss. The Company's net loss increased to approximately $14.7 million
for the quarter ended March 31, 1997 as compared to approximately $10.4
million for the same quarter of 1996.
 
 YEAR ENDED DECEMBER 31, 1996 COMPARED TO YEAR ENDED DECEMBER 31, 1995
 
  Revenue. Revenue totaled approximately $15.6 million for the year ended
December 31, 1996, an increase of $13.1 million over 1995 revenue of
approximately $2.5 million. This increase reflects continued growth in revenue
derived from Internet access customers, as well as revenue from the Company's
broadened enterprise product offerings and through the Company's leveraged
marketing arrangements with its strategic partners.The average selling prices
of the Company's offerings for consumer Internet access services decreased by
approximately 33% beginning in April 1996 due to industry-wide adoption of
flat monthly rates for unlimited Internet access.
   
  Cost of Revenue. Cost of revenue for the year ended December 31, 1996 was
approximately $47.9 million, an increase of $31.7 million from 1995 cost of
revenue of approximately $16.2 million. The largest component of this increase
was the cost of providing virtual local access ("VLA") service over 800
circuits. VLA service was an interim solution for providing nationwide
coverage, while the Company's SuperPOP network architecture was being
deployed. This deployment was substantially completed in December 1996. Costs
associated with VLA service are expected to be immaterial in amount in 1997.
The remainder of the increase in 1996 cost of revenue is primarily
attributable to the overall growth in the size of the network.     
 
  Network Equipment Write-off. In 1996, the Company took a charge of
approximately $8.3 million related to the cost of certain network equipment.
The Company decided not to deploy the equipment in the network because of
concerns that the equipment would not provide the functionality and
reliability required by the Company and concerns that the equipment provider
would be unable to provide timely maintenance and support. See Note 2 of Notes
to Financial Statements.
 
  Development. Development expense for the year ended December 31, 1996 was
approximately $2.4 million, an increase of $1.6 million over 1995 expenditures
of approximately $837,000. This higher level of development expense in 1996
primarily reflects an overall increase in personnel to develop new product
offerings and to manage the overall growth in the network.
 
 
                                      28
<PAGE>
 
  Marketing and Sales. Marketing and sales expense for 1996 was approximately
$16.6 million, an increase of $12.7 million over 1995 expenditures of
approximately $3.9 million. This increase in marketing and sales expense
reflects a substantial investment in the customer support, marketing and sales
organizations required to support the Company's expanded customer base. This
increase also reflects a growth in subscriber acquisition costs, related to
both increased direct marketing efforts as well as commissions paid to
distribution partners. Additionally, the increase reflects the ramp-up of
marketing efforts related to the introduction of enterprise products and
services.
 
  General and Administrative. General and administrative expense for 1996 was
approximately $3.4 million, an increase of $500,000 over 1995 expenditures of
approximately $2.9 million. This increase reflects an increase in personnel
and professional fees necessary to manage the financial, legal and
administrative aspects of the business.
 
  Net Interest Expense. Net interest expense for 1996 was approximately $3.3
million as compared to approximately $721,000 for 1995. The increase of $2.6
million is primarily due to an increase of $27.6 million in principal amount
of the capitalized lease obligations from December 31, 1995 to December 31,
1996. This increase in interest expense was partially offset by greater
interest income from higher average cash balances resulting from equity
financings completed in late 1995 and in August 1996. See Notes 3 and 6 of
Notes to Financial Statements.
 
  Net Loss. The Company's net loss increased to approximately $66.4 million in
1996 from approximately $22.0 million in 1995.
 
 YEAR ENDED DECEMBER 31, 1995 COMPARED TO YEAR ENDED DECEMBER 31, 1994
 
  Revenue. Revenue totaled approximately $2.5 million for 1995, an increase of
$2.1 million, over 1994 revenue of approximately $400,000. The Company's
revenue in 1995 reflects its first full year of providing network services.
The Company's revenue in both of these years was derived entirely from the
sale of Internet access services to consumers.
 
  Cost of Revenue. Cost of revenue for 1995 was approximately $16.2 million,
an increase of $13.3 million over 1994 cost of revenue of approximately $2.9
million. The increase in cost of revenue from 1994 to 1995 reflected overall
higher costs associated with deploying and managing the Company's own network
infrastructure. Prior to late 1994, the Company had leased third party network
facilities and thus had not incurred significant network deployment and
maintenance expenses.
 
  Development. Development expense for 1995 was approximately $837,000, an
increase of $303,000 over 1994 expenditures of approximately $534,000. This
higher level of development expense primarily reflected an overall increase in
personnel required to develop new products and support network growth.
 
  Marketing and Sales. Marketing and sales expense for 1995 was approximately
$3.9 million, an increase of $3.3 million over 1994 expenditures of
approximately $639,000. This higher level of spending in 1995 reflected the
Company's new market focus on providing IP-based network services. In
connection with this new focus, the Company incurred increased expenses
related to direct subscriber acquisition, formation of a telesales group,
development of strategic relationships and marketing communications. With the
growth in subscribers, the Company added personnel to its customer support
organization.
 
  General and Administrative. General and administrative expense for 1995 was
$2.9 million, an increase of $2.3 million over 1994 expenditures of
approximately $600,000. This increase generally reflects an increase in
personnel and professional fees necessary to manage the financial, legal and
administrative aspects of the business.
 
  Net Interest Expense. Net interest expense for 1995 was approximately
$721,000 as compared with approximately $57,000 for 1994. This increase in net
interest expense resulted from the Company's deployment of network equipment
for its own network infrastructure beginning in late 1994 which equipment
purchases were primarily financed under capital leases. Capital lease
obligations at December 31, 1995 were $14.2 million, compared with no such
obligations at December 31, 1994.
 
  Net Loss. The Company's net loss increased to approximately $22.0 million in
1995 from a net loss of $4.3 million in 1994.
 
                                      29
<PAGE>
 
QUARTERLY RESULTS OF OPERATIONS
 
  The Company's quarterly operating results can fluctuate from period-to-
period depending upon factors such as the success of the Company's efforts to
expand its subscriber and third party partnership base, changes in, and the
timing of, expenses relating to development and sales and marketing and
changes in pricing policies by the Company or its competitors. Management
believes that period-to-period comparisons of its financial results should not
be relied upon as an indication of future performance. The Company may
experience significant period-to-period fluctuations in operating results.
 
  The following tables set forth the statement of operations data for each of
the nine quarters through March 31, 1997, as well as the percentage of the
Company's revenue. This information has been derived from the Company's
unaudited financial statements. In the opinion of management, the unaudited
information set forth below has been prepared on the same basis as the audited
financial statements contained herein and includes all adjustments, consisting
only of normal recurring adjustments, except for the write-off of network
equipment in the three months ended December 31, 1996, necessary to present
fairly the information set forth herein. The operating results for any quarter
are not necessarily indicative of results for any future period.
 
<TABLE>
<CAPTION>
                                                       THREE MONTHS ENDED
                          ---------------------------------------------------------------------------------------------
                                        1995                                      1996                           1997
                          --------------------------------------   -----------------------------------------   --------
                          MAR. 31   JUNE 30   SEP. 30   DEC. 31    MAR. 31    JUNE 30    SEP. 30    DEC. 31    MAR. 31
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
                                                         (IN THOUSANDS)
<S>                       <C>       <C>       <C>       <C>        <C>        <C>        <C>        <C>        <C>
Revenue.................  $   413   $   632   $   691   $    747   $  1,533   $  2,489   $  4,193   $  7,433   $  9,154
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
Costs and operating
 expenses:
 Cost of revenue........    3,079     3,557     3,652      5,880      7,256     11,782     11,913     16,994     15,744
 Network equipment
  write-off.............      --        --        --         --         --         --         --       8,321        --
 Development............      126       186       239        286        340        571        692        846      1,025
 Marketing and sales....      302       474     1,260      1,863      3,120      3,868      4,045      5,576      4,936
 General and
  administrative........      129     1,124       396      1,217        736      1,036        727        946      1,060
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
 Total operating costs
  and expenses..........    3,636     5,341     5,547      9,246     11,452     17,257     17,377     32,683     22,765
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
Loss from operations....   (3,223)   (4,709)   (4,856)    (8,499)    (9,919)   (14,768)   (13,184)   (25,250)   (13,611)
Net interest expense....       10       262       209        240        461        652      1,289        858      1,070
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
Net loss................  $(3,233)  $(4,971)  $(5,065)  $ (8,739)  $(10,380)  $(15,420)  $(14,473)  $(26,108)  $(14,681)
                          =======   =======   =======   ========   ========   ========   ========   ========   ========
<CAPTION>
                                                       THREE MONTHS ENDED
                          ---------------------------------------------------------------------------------------------
                                        1995                                      1996                           1997
                          --------------------------------------   -----------------------------------------   --------
                          MAR. 31   JUNE 30   SEP. 30   DEC. 31    MAR. 31    JUNE 30    SEP. 30    DEC. 31    MAR. 31
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
<S>                       <C>       <C>       <C>       <C>        <C>        <C>        <C>        <C>        <C>
Revenue.................    100.0%    100.0%    100.0%     100.0%     100.0%     100.0%     100.0%     100.0%     100.0%
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
Costs and operating
 expenses:
 Cost of revenue........    745.6     562.8     528.5      787.1      473.3      473.4      284.1      228.6      172.0
 Network equipment
  write-off.............      --        --        --         --         --         --         --       112.0        --
 Development............     30.5      29.4      34.6       38.3       22.2       22.9       16.5       11.4       11.2
 Marketing and sales....     73.1      75.0     182.3      249.4      203.5      155.4       96.5       75.0       53.9
 General and
  administrative........     31.2     177.8      57.3      162.9       48.0       41.6       17.3       12.7       11.6
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
 Total operating costs
  and expenses..........    880.4     845.0     802.7    1,237.7      747.0      693.3      414.4      439.7      248.7
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
Loss from operations....   (780.4)   (745.0)   (702.7)  (1,137.7)    (647.0)    (593.3)    (314.4)    (339.7)    (148.7)
Net interest expense....      2.4      41.5      30.3       32.1       30.1       26.2       30.8       11.5       11.7
                          -------   -------   -------   --------   --------   --------   --------   --------   --------
Net loss................   (782.8)%  (786.5)%  (733.0)% (1,169.8)%   (677.1)%   (619.5)%   (345.2)%   (351.2)%   (160.4)%
                          =======   =======   =======   ========   ========   ========   ========   ========   ========
</TABLE>
 
  The Company's quarterly operating results have fluctuated and will continue
to fluctuate from period to period depending upon factors such as the timely
deployment and implementation of expansion of the Concentric network and new
network architectures, the incurrence of related capital costs, the receipt of
new value-added network services and consumer services subscriptions and the
introduction of new services by the Company and its competitors. Additional
factors that may contribute to variability of operating results include: the
payment of statutory interest related to the rescission offer; the pricing and
mix of services offered by the Company; customer retention rate; market
 
                                      30
<PAGE>
 
acceptance of new and enhanced versions of the Company's services; changes in
pricing policies by the Company's competitors; the Company's ability to obtain
sufficient supplies of sole- or limited-source components; user demand for
network and Internet access services; balancing of network usage over a 24-
hour period; and general access services.
 
  In view of the significant growth of the Company's operations, the Company
believes that period-to-period comparisons of its financial results should not
be relied upon as an indication of future performance and that the Company may
experience in the future significant period-to-period fluctuations in
operating results. The Company expects to focus in the near term on building
and increasing its revenue base, which will require it to significantly
increase its expenses for personnel, marketing, network infrastructure and the
development of new services, and may adversely impact short term operating
results. As a result, there can be no assurance that the Company will be
profitable on a quarterly basis in the future and the Company believes that it
will incur losses in the near term.
 
LIQUIDITY AND CAPITAL RESOURCES
 
  To date, the Company has satisfied its cash requirements primarily through
capitalized lease financings and the sale of capital stock. The Company's
principal uses of cash are to fund working capital requirements and capital
expenditures and to service its capital lease financing obligations. Net cash
used in operating activities for the three months ended March 31, 1997 and
1996 was approximately $11.1 million and $8.4 million, respectively. Net cash
used in investing activities for the three months ended March 31, 1997 and
1996 was approximately $2.5 million and $500,000, respectively. For the three
months ended March 31, 1997 and 1996, cash of approximately $1.2 million and
$800,000, respectively, was used in financing activities. Cash used in the
first quarter of 1997 is net of $1.1 million cash received from a current
investor for rights to purchase warrants, which warrants were subsequently
issued.
 
  Net cash used in operating activities for the years ended December 31, 1996,
1995 and 1994 was approximately $42.1 million, $15.8 million and $2.6 million,
respectively. Net cash used in investing activities was approximately $7.3
million, $1.2 million and $1.0 million for 1996, 1995 and 1994, respectively.
Net cash flow provided by financing activities was approximately $48.1
million, $36.0 million and $3.7 million for 1996, 1995 and 1994, respectively.
Cash provided by financing activities in 1996 includes approximately $53.5
million net proceeds from the issuance of Series D Preferred Stock, while 1995
reflects net proceeds from the issuance of Series A Preferred Stock, Series B
Preferred Stock and Series C Preferred Stock, totaling approximately $34.8
million.
 
  The Company used approximately $6.9 million, $1.4 million and $791,000 of
cash to purchase capital equipment and leasehold improvements in 1996, 1995
and 1994, respectively, and approximately $2.5 million in the three months
ended March 31, 1997. To date, the Company primarily has used capital lease
arrangements to finance capital equipment purchases and the principal amount
of such lease financing obligations totaled $47.7 million at March 31, 1997.
The Company currently has financing availability under the following equipment
lease facilities: (i) a master lease agreement with no minimum or maximum for
the lease financing of equipment sold and/or manufactured by Racal; (ii) a
master lease agreement which currently authorizes up to a maximum of $3.3
million in the aggregate for lease financing of telecommunications and
computer equipment which was fully utilized at March 31, 1997; and (iii) a
master lease agreement of up to a maximum of $2.0 million in the aggregate for
lease financing of telecommunications and computer equipment, of which
approximately $1.7 million had been utilized at March 31, 1997. In addition,
the Company is contemplating entering into negotiations for a lease financing
facility to finance its telecommunications and computer equipment requirements
for the remainder of 1997. See Note 3 of Notes to Financial Statements.
 
  The Company has already made significant capital investments in its network,
data centers, development equipment and other capital assets totaling
approximately $39.1 million, $17.2 million and $800,000 in 1996, 1995 and
1994, respectively. The Company expects to make additional investments in
capital equipment to expand and enhance its network, with approximately $8.0
million of anticipated purchases of capital equipment throughout the remainder
of 1997, of which the Company plans to finance approximately $5.0 million
through capital lease arrangements. The foregoing expectation with respect to
additional capital investments is a forward-looking statement that involves
risks and uncertainties and the actual amount of capital investment could vary
materially as a result of a number of factors, including those described in
"Risk Factors--Future Capital Needs; Uncertainty of Additional
 
                                      31
<PAGE>
 
Financing." In addition, the Company may be obligated to repurchase shares
tendered in connection with the Company's Rescission Offer for a maximum
liability of approximately $1.4 million plus statutory interest of
approximately $300,000 with respect to shares issued on conversion of the
convertible debentures and an amount of approximately $940,000 with respect to
certain options issued by the Company. See Note 5 of Notes to Financial
Statements and "Risk Factors--Rescission Offers."
 
  Since the Company expects to incur additional operating losses, the Company
will rely on the following to meet its near term capital requirements: (i) the
contemplated lease financing discussed above; and (ii) the net proceeds from
this offering and the Direct Placements. The Company believes that such
financing will be sufficient to meet its anticipated cash needs for working
capital and for the acquisition of capital equipment at least for the next 12
months. However, there can be no assurance that the Company will not require
additional financing within this time frame. The Company's forecast of the
period of time through which its financial resources will be adequate to
support its operations is a forward-looking statement that involves risks and
uncertainties, and actual results could vary. The Company may be required to
raise additional funds through public or private financing, strategic
relationships or other arrangements. There can be no assurance that such
additional funding, if needed, will be available on terms attractive to the
Company, or at all. Furthermore, any additional equity financing may be
dilutive to stockholders, and debt financing, if available, may involve
restrictive covenants. Strategic arrangements, if necessary to raise
additional funds, may require the Company to relinquish its rights to certain
of its technologies. See "Risk Factors--Future Capital Needs; Uncertainty of
Additional Financing."
 
IMPACT OF ADOPTION OF NEW ACCOUNTING STANDARDS
 
  In October 1995, the Financial Accounting Standards Board issued Statement
of Financial Accounting Standards No. 123 "Accounting for Stock-Based
Compensation" ("FAS 123"), which established a fair-value based method of
accounting for stock-based compensation plans and requires additional
disclosures for those companies that elect not to adopt the new method of
accounting. In January 1996, the Company adopted the disclosure requirements
of FAS 123. The Company accounts for stock-based compensation in accordance
with Accounting Principles Board Opinion No. 25, "Accounting for Stock Issued
to Employees." The adoption of the disclosure requirements of FAS 123 did not
have a material impact on the Company's financial condition or results of
operations.
 
  In February 1997, the Financial Accounting Standards Board issued Statement
of Financial Accounting Standards No. 128, "Earnings per Share" ("FAS 128"),
which adjusts the calculation of earnings per share under generally accepted
accounting principles. FAS 128 is effective for the Company's fiscal year
ending December 31, 1997. See Note 1 of Notes to Financial Statements for the
effect of FAS 128 on the Company's pro forma net loss per share presentation.
 
                                      32
<PAGE>
 
                                   BUSINESS
 
  Concentric provides tailored, value-added Internet Protocol ("IP") based
network services for businesses and consumers. To provide these services, the
Company utilizes its low/fixed latency, high-throughput network, employing its
advanced network architecture and the Internet. Concentric's service offerings
for enterprises include virtual private networks ("VPN's"), dedicated access
facilities and Web hosting services. These services enable enterprises to take
advantage of standard Internet tools such as browsers and high-performance
servers for customized data communications within an enterprise and between an
enterprise and its suppliers, partners and customers. These services combine
the cost advantages, nationwide access and standard protocols of public
networks with the customization, high performance, reliability and security of
private networks. Among the current enterprise customers are Acer America
Corporation, Inc., Intuit, Inc., Total Entertainment Network, WebTV Networks,
Inc. and Ziff-Davis Publishing Co. Concentric's service offerings for
consumers and small office/home office customers include local Internet dial-
up access, Web hosting services and online multiplayer gaming.
 
INDUSTRY BACKGROUND
 
 Development of Private Networks
 
  Historically, the data communications services offered by public carriers
had limited security features, were expensive and did not adequately ensure
accurate and reliable transmission. As a result, many corporations established
and maintained their own private wide-area networks ("WANs") to provide
network-based services, such as transaction processing, to their customers and
to coordinate operations between employees, suppliers and business partners.
Such private WANs were frequently customized to specific applications,
business practices and user communities. As a result, these private WANs had
the capability of providing organizations and users with tailored performance
and features, security, reliability and private-label branding.
 
  The demand for WANs has grown as a result of today's competitive business
environment. Factors stimulating the higher demand include the need to provide
broader and more responsive customer service, to operate faster and more
effectively between operating units, suppliers and other business partners,
and the need to take advantage of new business opportunities for network-based
offerings in a timely fashion. In addition, as businesses become more global
in nature, the ability to access business information across the enterprise
has become a competitive necessity.
 
  Despite the attractive capabilities of private networks, limitations of many
private WANs have impeded or reduced the effectiveness of their use. These
networks, which traditionally have required the use of leased telephone lines
with bandwidth dedicated solely to this purpose and the purchase of vendor-
specific networking equipment, are inherently expensive to set up, operate and
maintain. Private WANs often require the development and maintenance of
proprietary software and lack cost-effective access. These aspects of
developing, deploying and maintaining such private WANs have conflicted with
the increased focus of many businesses on their core competencies, which has
prompted the outsourcing of many noncore functions. The Company believes that
many businesses have viewed as unacceptable the costs of maintaining a private
WAN infrastructure and the risks of investing in new technologies in the
absence of a single technological standard.
 
 Emergence of the Internet
 
  The emergence of the Internet and the widespread adoption of IP as a data
transmission standard in the 1990s, combined with deregulation of the
telecommunications industry and advances in telecommunications technology have
significantly increased the attractiveness of providing data communication
applications and services over public networks. At the same time, growth in
client/server computing, multimedia personal computers and online computing
services and the proliferation of networking technologies have resulted in a
large and growing group of people who are accustomed to using networked
computers for a variety of purposes, including e-mail, electronic file
transfers, online computing and electronic financial transactions. These
trends have led businesses increasingly to explore opportunities to provide
IP-based applications and services within their organization, and to customers
and business partners outside the enterprise.
 
 
                                      33
<PAGE>
 
 Need for IP-Based Private Networks
 
  The ubiquitous nature and relatively low cost of the Internet have resulted
in its widespread usage for certain applications, most notably Web access and
e-mail. However, usage of the Internet for mission-critical business
applications has been impeded by the limited security and unreliable
performance inherent in the structure and management of the Internet.
Additionally, emerging applications such as IP-based voice and video
applications, multiplayer gaming and certain multimedia applications require a
network that has high performance characteristics, including low and/or fixed
latency (response time) and high throughput, as well as the ability to
customize features for specific user requirements. On the Internet, latency is
frequently relatively high and variable, making it suboptimal for these
emerging applications. Although private networks are capable of offering lower
and more stable latency levels, providers of these emerging applications also
desire a network that will offer their customers full access to the Internet.
As a result, these businesses and applications providers require a network
that combines the best features of the Internet, such as openness, ease of
access and low cost made possible by the IP standard, with the advantages of a
private network, such as high security, low/fixed latency and customized
features.
 
  Industry analysts expect the market size for both value-added IP data
networking services and Internet access to grow rapidly as businesses and
consumers increase their use of the Internet, intranets and privately managed
IP networks. The total market for these services is projected to grow from
$1.2 billion in 1996 to approximately $22.7 billion in the year 2000, with
approximately $10.4 billion in the enterprise market segment and $12.3 billion
in the consumer market segment.
 
THE CONCENTRIC SOLUTION
 
  Concentric provides tailored, value-added IP-based network services for
businesses and consumers. To provide these services, the Company employs a
low/fixed latency, high-throughput network based on its advanced,
geographically dispersed ATM and frame relay backbone and the Internet.
Concentric allows enterprises to create virtual private networks providing
tailored network access, content and services to enterprise-defined end users
with higher reliability and more security than is available over the Internet.
Concentric's VPN solutions also provide the ease of access and flexibility of
public networks at a lower cost than private WANs without sacrificing
reliability or security.
 
  The Concentric network employs an advanced, geographically dispersed ATM and
frame relay backbone, SuperPOPs in 14 major metropolitan areas and 132
secondary and tertiary POPs in other cities, allowing dial-up network access
in the U.S. and Canada. In addition, the Company can provide analog dial-up,
frame relay, fractional T-1, T-1 and DS3 access to the network. The Concentric
network is engineered and managed to provide superior quality of service,
balancing several key performance criteria. The Company provides guaranteed
levels of service for dedicated access facilities to enterprise customers, and
targets performance benchmarks for connection success rates, latency levels
and throughput for all of its service offerings. Concentric also believes that
a major advantage of its network architecture is its ability to perform
adaptive call processing ("ACP"), which is designed to enable the tuning of
network parameters and traffic routing to meeting the latency, throughput,
security, and reliability requirements of a specific customer or application
on a call-by-call basis. Concentric is currently deploying the ACP technology
in its network and is planning to commercially introduce ACP capabilities
during the second half of 1997.
 
  In addition to strong network performance capabilities, the Company believes
that several factors distinguish its ability to provide value-added network
services. These factors include: (i) excellent service quality; (ii) rapid
development time and flexibility in meeting custom applications requirements;
(iii) responsive customer support and effective account management, available
24 hours per day, seven days per week through the Company's 142 customer
service personnel; and (iv) the Company's technical expertise in devising
cost-effective network solutions for customers.
 
                                      34
<PAGE>
 
BUSINESS STRATEGY
 
  The Company's objective is to become the leading supplier of value-added,
IP-based network services worldwide. In order to achieve this goal, the
Company is implementing a business strategy focused on the following key
principles:
 
  Rapidly Provide Cost-Effective, Tailored Network Solutions. The Company
intends to capitalize on its expertise in developing tailored VPNs to
establish a leadership position in rapidly developing, deploying and
maintaining a range of value-added network services to meet the specific needs
of its customers. The Company utilizes a set of software and hardware
technology modules as "building blocks" to offer a variety of tailored network
services on an IP-based network architecture with minimal additional
investment in engineering and rapid time to market for businesses and
consumers. These building blocks include modules for client and system
software, dedicated and remote network connectivity, tracking and billing, Web
hosting, customer support and security.
 
  Optimize Network Utilization. Given the fixed cost nature of Concentric's
network infrastructure, the Company strives to increase total network
utilization and to optimize this utilization by targeting both daytime
business and evening-intensive consumer users to balance the network's usage
throughout a 24-hour period. Accordingly, while the Company's current
strategic focus is on providing value-added IP-based communications services
to enterprises, the Company intends to continue partnering with multichannel
distributors to acquire and maintain a base of consumer subscribers who access
the Concentric network predominantly during non-business hours.
 
  Employ Leveraged Marketing Through Strategic Partners. The Company actively
seeks to form alliances with certain software developers, gaming companies,
and telecommunications service and equipment suppliers that have substantially
greater marketing, distribution and sales resources than does the Company and
that have a large installed customer base. These alliances facilitate the
cost-effective acquisition of consumer and business customers and increase
Concentric's network utilization. These marketing relationships are developed
and enhanced through the bundling of Concentric's IP-based network services
with the products and services offered by the strategic partners. These
relationships may involve customized browsers, registration services and
specialized pricing, commissions and billing programs. To date, Concentric has
established such strategic relationships with a number of companies, including
Acer America Corporation, Bay Networks, Inc., Intuit, Inc., Microsoft
Corporation, Netscape, PictureTel Corporation ("PictureTel"), Racal-Datacom,
Inc., Telecom Italia and WebTV Networks, Inc. ("WNI"). See "--Key Customer
Applications" and "Sales and Marketing."
 
  Offer Next Generation Network Services. The Company is continuing to expand
the value-added network services that it makes available to its customers.
Towards this end, the Company is in early stage trials with providers of video
conferencing and IP-based telephony services that require the low/fixed
latency characteristics afforded by the Concentric network. Additionally, the
Company is applying for licenses to become a Competitive Local Exchange
Carrier ("CLEC") in selected states. The Company believes that successful
implementation of its CLEC strategy will enable the Company to reduce its
local access charges, as well as to expand its range of services.
 
  Deploy Network Services Internationally. The Company believes that its
enterprise customers increasingly will require their network solutions
providers to offer network services on a global basis. Pursuant to an
agreement with TMI Telemedia International, Ltd., a subsidiary of Telecom
Italia SpA ("TMI"), entered into in August 1996, the Company is working to
establish an international network based on Concentric's network technology
and expertise and TMI's existing telecommunications infrastructure to deliver
a range of compatible network services worldwide. TMI currently has a
telecommunications network deployed in over 40 countries worldwide.
Additionally, the Company entered into a roaming services agreement in June
1997 with NTT PC Communications, Inc. ("NTT PC"), a leading provider of IP
services in Japan. The roaming services agreement allows Concentric customers
to use the NTT PC network to access their internet accounts in Japan and
allows members of the NTT PC network to access their internet accounts in the
United States and Canada. While the Company does not expect to generate
significant revenue from deployment of international network services until at
least 1998, the Company believes that the ability to deliver network solutions
globally will be a key competitive factor in its industry.
 
                                      35
<PAGE>
 
SERVICES
 
  Concentric provides tailored, value-added IP-based network services for
businesses and consumers. To provide these services, the Company employs a
low/fixed latency high-throughput network based on an advanced, geographically
dispersed ATM and frame relay backbone and the Internet.
 
 Enterprise Solutions
 
  For businesses, the Company has developed a set of enterprise services
including VPNs, dedicated and remote access services and Web hosting services.
 
  VPNs. Concentric's VPN solutions enable its customers to deploy tailored,
IP-based mission-critical business applications for internal enterprise,
business-to-business and business-to-customer data communications on the
Concentric network while also affording high-speed access to the Internet.
Concentric offers its customers a secure network on which to communicate and
access information between an organization's geographically dispersed
locations; collaborate with external groups or individuals, including
customers, suppliers, and other business partners and use the Web to access
information on the Internet and communicate with other Web users. The
Company's VPN solutions allow the enterprise customer to tailor the type of
access, services and information that various users of the VPN are afforded
according to the specific needs of the enterprise.
 
  The Company's VPN building blocks include modules for client and system
software, network connectivity (high-speed dedicated access lines, remote
access services and dial-up accounts), tracking and billing, Web hosting
(intranet, Web, e-mail, news or other servers), customer support and security.
VPN customers may choose to use one or more of the elements individually or in
tandem with existing or third-party components to create a customized
networking solution that is generally superior in terms of price, performance
and time to market to the option of building and maintaining a private
network. Key benefits include rapid implementation time, lower operating and
maintenance costs, minimal capital investment, higher quality of service
overall and 24-hour network and customer support.
 
  For example, starting in October 1995 the Company created and now maintains
the VPN used by Intuit customers using a customized version of the Netscape
Navigator browser bundled with Quicken for Windows, Quickbooks, ProTax and
TurboTax. The bundled software allows a Quicken customer to click on an icon
that launches Netscape, and takes the user directly to Quicken Financial
Network Website. On the Web page Quicken customers will find useful financial
advice, information from Intuit's bank and financial institution partners,
answers to commonly asked technical questions and tips on how to tap the full
potential of Intuit's financial products. See "--Key Customer Applications."
 
  Pricing options for enterprise solutions are a combination of standard
prices and standard charges for integration of the Company's VPN building
blocks into a comprehensive package. VPN services are priced by combining
elements such as dedicated access facilities and Web hosting with customer
support, software and other Concentric building blocks. The pricing is
standard for each service, but may be combined as a package with quantity
discounts.
 
  Dedicated Access Facilities. In January 1997, the Company began offering
dedicated access facilities ("DAFs") as a stand-alone product targeted at
businesses that desire single or multipoint high-speed, dial-up and/or
dedicated connections to distributed locations such as regional offices,
warehouses, manufacturing facilities and/or to the Internet. DAF products are
primarily targeted at providing intranet connectivity amongst distributed
enterprise locations with the additional benefit of Internet access if desired
by the customer. The Company provides a full range of connectivity options,
allowing the customer to order the appropriate amount of bandwidth to meet its
networking requirements. In addition, Concentric offers its DAF customers a
guarantee on the quality of service and performance of these facilities.
Furthermore, Concentric believes it is the only network service provider to
bill customers based on average usage levels rather than peak usage levels.
 
  Concentric also performs around-the-clock monitoring of network performance
and enables its customers to monitor their network as well through the
Company's proprietary ConcentricView software. ConcentricView is a
 
                                      36
<PAGE>
 
distributed Web-based network management tool that enables a customer to
monitor usage on a call-by-call basis and performance of that portion of the
Concentric network bandwidth supporting the customer's applications. The
Company believes it is the only network services provider to offer this
service.
 
  Concentric has four offerings in its dedicated access product line:
FullChannel T-1, FullChannel T-1 Protected, FlexChannel and LECFrame Relay.
 
                            FULLCHANNEL T-1 PRICING
 
<TABLE>
<CAPTION>
- ------------------------------------------------------------------------------------------
     ONE-TIME FEE               AVERAGE USAGE LEVEL                         MONTHLY FEE(1)
     ------------               -------------------                         --------------
     <S>                        <C>                                         <C>
      $3,000.00                        0-64Kbps                               $1,095.00
      $3,000.00                      64-128Kbps                               $1,595.00
      $3,000.00                     128-256Kbps                               $2,095.00
      $3,000.00                     256-384Kbps                               $2,395.00
      $3,000.00                       384Kbps +                               $2,695.00
- ------------------------------------------------------------------------------------------
</TABLE>
                       FULLCHANNEL T-1 PROTECTED PRICING
 
<TABLE>
<CAPTION>
     ONE-TIME FEE               AVERAGE USAGE LEVEL                         MONTHLY FEE(1)
     ------------               -------------------                         --------------
     <S>                        <C>                                         <C>
      $3,000.00                      384Kbps +                                $2,095.00
- ------------------------------------------------------------------------------------------
</TABLE>
                              FLEXCHANNEL PRICING
 
<TABLE>
<CAPTION>
     ONE-TIME FEE            FRACTIONAL T-1 BANDWIDTH                   MONTHLY FEE(1)
     ------------            ------------------------                   --------------
     <S>                     <C>                                        <C>
      $3,000.00                      128Kbps                              $  895.00
      $3,000.00                      256Kbps                              $1,295.00
      $3,000.00                      384Kbps                              $1,595.00
      $3,000.00                      512Kbps                              $1,895.00
- --------------------------------------------------------------------------------------
</TABLE>
                           LECFRAME RELAY PRICING(2)
 
<TABLE>
<CAPTION>
     ONE-TIME FEE          FRAME RELAY               CIR(3)                MONTHLY FEE(1)
     ------------          -----------               -------               --------------
     <S>                   <C>                       <C>                   <C>
      $2,000.00               56Kbps                  32Kbps                 $  395.00
      $2,000.00              128Kbps                  64Kbps                 $  795.00
      $2,000.00              256Kbps                 128Kbps                 $  995.00
      $2,000.00              512Kbps                 256Kbps                 $1,095.00
- ------------------------------------------------------------------------------------------
</TABLE>
(1) Monthly billing based on average usage.
(2) Offer varies by region.
(3) Committed Information Rate.
 
  FullChannel T-1 pricing is based on average utilization pricing. The
customer's usage is measured at five-minute intervals throughout the month,
and the average of all of those measurements is used to determine the
customer's bill at the end of the month. This is the appropriate choice for
those customers who have fluctuating and/or uncertain bandwidth consumption
patterns.
 
  FullChannel T-1 Protected gives a customer a fixed price for a full 1.5
megabits of bandwidth. This is an economical choice for those customers who
recognize in advance that their bandwidth throughput requirements will equal
T-1 levels.
 
  FlexChannel gives a customer the opportunity to purchase a fractional
portion of a T-1 for a fixed monthly fee. This is the appropriate choice for
the customers who know that their bandwidth requirements are going to be
consistently less than a full T-1.
 
  LECFrame Relay is based on various LECs' Frame Relay facilities. Although
Concentric does not offer service level guarantees over LECFrame Relay,
Concentric does guarantee the committed information rate ("CIR"). This
 
                                      37
<PAGE>
 
offering gives a lower cost, lower performance network service for those
customers for whom performance is less imperative.
 
  Web Hosting Services. The Company's Web hosting services were introduced in
March 1997, and are targeted at businesses that are implementing high-
performance intranet, Web, e-mail, gaming, chat or other types of services.
Concentric offers a wide range of hosting solutions structured to meet the
needs of small businesses to very large enterprises. By outsourcing its Web
hosting requirements to Concentric, an enterprise can reduce costs while
increasing reliability and performance of its servers.
 
  Web hosting consists of providing and/or managing the necessary equipment to
allow companies to operate Web sites. The components of Web hosting are the
server; a workstation or PC that runs the Website; the facility to host the
server; high speed Internet access for hosted servers; server and power backup
to ensure 24 hour functionality; and maintenance to ensure ongoing operation
of the server. Concentric also bundles Web hosting software and network
services to provide businesses with complete Internet presence solutions.
 
                              WEB HOSTING PRICING
 
- --------------------------------------------------------------------------------

        CONCENTRIC NETWORK                                        SMALL
      SHARED HOSTING SERVICES                               ENTERPRISE HOSTING
      -----------------------                               ------------------
          Internet Access                                          Yes
              Address                                         Virtual Domain
          Email Accounts                                            10
         Web site storage                                         30 MB
        Monthly Throughput                                       1000 MB
            Set-up Fee                                           $100.00
           Monthly Price                                          $59.95

- -------------------------------------------------------------------------------
 
                      DEDICATED CO-LOCATED SERVER PRICING
 
         INTERNET CONNECTION                                     MONTHLY PRICE
         -------------------                                     -------------
      1 Mbps Priority Bandwidth                                    $1,500.00
      2 Mbps Priority Bandwidth                                    $2,500.00
      4 Mbps Priority Bandwidth                                    $4,500.00
      Dedicated 10 Mbps Ethernet                                   $6,000.00
              Setup Fee                                            $1,000.00
- --------------------------------------------------------------------------------

   
  Pursuant to a Co-Marketing Services Agreement, a Trademark License Agreement
and a Software License Agreement executed as of June 23, 1997 (the
"Agreements"), the Company entered into a strategic business arrangement with
Netscape to design, develop and operate Netscape Virtual Office by Concentric,
to offer customers hosted private Intranet services that can be accessed from
anywhere on the Internet. The service is being adapted from Concentric's
ConcentricHost product and will use Netscape's SuiteSpot software features.
These Intranet services are designed to give an individual or small business
with an Internet connection the ability to establish a "Virtual Office" that
is accessible through Netscape's Internet site. Launch of the service
currently is planned for late 1997. The Agreements have an initial term of two
years, which may be renewed for up to two additional one year terms. The
geographic scope of the licenses granted by Netscape are sufficient to enable
the Company to operate Netscape Virtual Office by Concentric as currently
planned by the Company. Pursuant to the Agreements, the Netscape Virtual
Office by Concentric will feature the latest versions of Netscape SuiteSpot
server software family for Web, messaging and collaboration applications. The
service is to be jointly designed by the Company and Netscape and will be
developed, hosted and maintained by the Company. Upon execution of the
Agreements the Company made a $2.0 million down payment to Netscape. See
"Certain Transactions--Bridge Loans."     
 
  Netscape Virtual Office by Concentric is being designed to give individual
professionals, small businesses and project groups a private online presence
that can be shared with co-workers or other specified users. This online
 
                                      38
<PAGE>
 
Intranet center would serve as a user's entry point to a wide variety of
online information management services, such as HTML email accounts, internal
and external Web sites, private discussion forums and project collaboration,
without the cost of extensive hardware, software and technical personnel. To
take advantage of these services, the user would only need Internet access and
Netscape Communicator client software. In order to create a "Virtual Office,"
the user or office manager would sign up for the monthly service on the
Netscape Internet site. The user would initially specify basic information,
project parameters, a list of people who can access the Virtual Office, and
credit card information for payment. Once all information is specified, the
user's Virtual Office would be automatically configured.
 
  Remote Access Service. The Company's remote access services ("RAS"), are
marketed as Concentric RemoteLink, and were released commercially in mid-1997.
RemoteLink services are targeted at businesses that have employees in remote
locations. RemoteLink enables an enterprise's salespeople and other mobile
employees, telecommuters and business partners to dial into an enterprise's
corporate network resources and use them as if they were connected locally,
thus increasing their potential productivity and allowing for information to
be available on a real-time basis across the enterprise. Concentric's
RemoteLink is designed to be highly customizable and has the ability to
interface with existing Company network infrastructure. Additionally,
RemoteLink is being designed to support multiple layers of security including
privacy encryption, local and remote firewalls and network access security.
 
  The Company believes that RemoteLink will help businesses significantly
reduce the high costs of telecommunications charges and user support
associated with building, deploying and maintaining their own remote access
WAN, typically based on remote access servers or modem pools, 800 circuits and
router links to the Internet. In addition, the enterprise utilizes
Concentric's high-performance network, combined with T1 or fractional T1 links
to the enterprise LAN, offering more reliable and faster access. Concentric
RemoteLink offers support for remote users 24 hours a day, seven days a week.
See "Risk Factors--Dependence on New and Enhanced Services."
 
 Consumer Services
 
  Concentric provides its individual and small office/home office ("SOHO")
customers with a broad range of Internet access options and Web hosting e-
mail, chat, File Transfer Protocol ("FTP"), Gopher and online shareware
services. Users can choose from 800-number, telnet and direct dial services.
Concentric offers the Netscape Navigator or Microsoft Internet Explorer
browser to its users when they sign up for dial-up or 800-number service.
 
                            INTERNET ACCESS PRICING
 
<TABLE>
<CAPTION>
- --------------------------------------------------------------------------------
  PLAN                      MONTHLY FEE                ADDITIONAL TIME
  ----                      -----------                ---------------
  <S>                       <C>               <C>
  Starter Plan                $ 7.95          $1.95/hr after 5 hrs
  Standard Plan               $19.95          No charges for additional time.
                                              Unlimited active access for one
                                              monthly fee.
  800-number Plan             $10.00          $5/hr after 2 hrs
  Inbound Internet Plan       $10.00          No charges for additional time.
                                              Unlimited active access for one
                                              monthly fee.
- --------------------------------------------------------------------------------
</TABLE>
 
                              WEB HOSTING PRICING
 
<TABLE>
<CAPTION>
        CONCENTRIC NETWORK
      SHARED HOSTING SERVICES                              HOME OFFICE HOSTING
      -----------------------                              -------------------
      <S>                                                  <C>
          Internet Access                                          Yes
              Address                                           Subdomain
          Email Accounts                                            5
         Web site storage                                         5 MB
        Monthly Throughput                                       300 MB
            Set-up Fee                                           $50.00
           Monthly Price                                         $29.95
- --------------------------------------------------------------------------------
</TABLE>
 
                                      39
<PAGE>
 
  Concentric also offers a variety of shell accounts, including PPP, SLIP and
UNIX, as access solutions to users who do not require a graphical user
interface. Shell accounts also enable users who already have Internet access to
set up extra mailboxes or post their own Website. Shell account services
currently are priced at $10.00 per month.
 
  The Company also offers DAFs to its SOHO and individual customers. These
customers use these facilities to connect their Web servers to the Concentric
network (and hence to the Internet) or to offer dedicated connection to an
internal SOHO local area network.
 
  The Company also offers consumers value-added services, including a
collection of online multiplayer games and premium products targeted to
vertical segments such as the SOHO and family market. This includes the
upselling of discounted products and services in such areas as education,
retail products, telephony, and travel services with such partners as
Infonautics, Amazon.com, Inc. and QuadraCom, LLC. Such arrangements not only
provide a profitable monthly revenue stream but also increase customer
retention. Additional value-added products/services being reviewed by the
Company for potential introduction include premium service levels, critical
file disk back-up/recovery, hard drive maintenance software, virus protection,
and long distance and faxing services.
 
  Game Gateway. Concentric launched its Game Gateway in June 1997 as a broad
offering of online multiplayer games, affording consumers access to a number of
the major online gaming networks with the convenience of a single billing
account, login identification and password. The Game Gateway is offered to the
public via the Internet and provides access to 27 online games from 4 game
networks, including Engage, Gamestorm (Kesmai), Oceanline (Infogrames) and
Online Entertainment PLC.
 
  The Game Gateway offers a unified packaged solution of major online game
networks focusing on ease of use and advanced functionality. Game Gateway
customers are offered a free CD-ROM with additional value added offerings
including free content, game software and free time online. The Company's
relationship with Unified Gamers Online, LLC provides the Game Gateway with
experts that manage tournaments and other game-oriented activities like chats
and message boards. Concentric currently charges $1.75 per hour for all games
accessed through the Game Gateway.
 
CUSTOMERS
 
  The following is a representative list of the Company's customers during the
last 12 months.
 
  Acer America Corporation               Netlink, LTD
  Ameritech Services, Inc.               Netscape Communications Corporation
  Bascom Global Internet Services, Inc.  On Command Corporation
  Bay Networks, Inc.                     Peapod L.P.
  Books That Work                        PictureTel Corporation
  Corel Corporation                      SCP Communications
  Electronic Data Systems Corporation    SMC Communications LLC
  ENGAGE Games Online, Inc.              Scopus Technology, Inc.
  The Groovey Corporation                Sega of America, Incorporated
  Hewlett-Packard Company                Surfers Unlimited LLC
  Imagesoft Technologies, Inc.           Toshiba America Information Systems
  Investools, Inc.                       Total Entertainment Network
  Infonautics Corporation                WebTV Networks, Inc.
  Intuit, Inc.                           You Bet! On-Line Entertainment
  Microsoft Corporation                  Ziff-Davis Publishing Co.
 
  During the year ended December 31, 1996 and the three months ended March 31,
1997, revenue from WebTV accounted for 10.1% and 32.7%, respectively, of the
Company's revenue. See "Risk Factors--Customer Concentration."
 
 
                                       40
<PAGE>
 
KEY CUSTOMER APPLICATIONS
 
  The Company aggressively pursues business alliances with a variety of
companies. Through these partners, the Company seeks to expand its enterprise
and consumer customer base and increase the 24 hour utilization of the
Concentric network. The following is a summary of selected strategic
relationships:
 
    Intuit. Intuit Inc. ("Intuit"), a financial software and Web-based
  services company, is a market leader in personal and small business
  financial software. Intuit's mission is to change for the better how people
  and small businesses manage their financial lives, and to change for the
  better how financial providers reach, sell, and serve their customers and
  prospects. Intuit views its Websites as a key channel for communicating
  with its customers, and as a vehicle to provide personal finance,
  investment and tax related financial information. Concentric and Intuit
  partnered in October 1995 to launch the integrated Internet access to the
  Quicken Financial Network and the Internet. The Internet access capability
  included both a virtual private network service designed to provide Intuit
  customers subsidized access to select Intuit Web sites and the ability to
  upgrade to full access to the Internet. Intuit has bundled tailored
  versions of the Netscape Navigator browser in its fiscal year 1996 and 1997
  releases of Quicken, TurboTax, ProTax and Quickbooks. Concentric designed
  and implemented tailored registration and network access software to
  provide Intuit customers with seamless, subsidized access to select Intuit
  Web sites. Concentric provides an easy, Web-based upgrade process for
  customers desiring full Internet access and e-mail services. Customers are
  billed for network time through Concentric's billing systems. In addition,
  Concentric provides private-labeled customer service to Intuit customers
  with full network access on a twenty-four hour a day, seven day a week
  basis.
 
    WebTV Networks Inc. WebTV Networks Inc. ("WNI") provides the world's
  first high-quality Internet solution for television. In the fall of 1996,
  WNI's licensees, Sony Electronics, Inc. and Philips Electronics introduced
  a plug-and-play set-top box that enables Internet browsing from a
  television. As part of the WNI service, Concentric and WNI jointly designed
  and implemented a national virtual private dial-up network solution to
  connect WebTV Network(TM) users to the Internet, utilizing Concentric's
  network. The WebTV(TM) Internet terminal, combined with the virtual private
  network, allows anyone to browse the Internet from the comfort of their
  living room.
 
    You Bet! On-Line Entertainment. You Bet! On-Line Entertainment ("You
  Bet!") is a technology company that facilitates live events and is focused
  on content development, network deployment, and event management via a
  cross-platform environment. You Bet! is a service organization providing
  horse players instant access to live racing, information, and wagering
  worldwide via a private, secure online environment. The Company's initial
  service, the You Bet! Racing Network is focused on the emerging market for
  home wagering on domestic horse racing. The application, which runs on the
  Concentric network, involves the synchronization of audio, video and data
  feeds that are accumulated at a single point. The multicast application is
  supported by a secure front-end processor and maintained at the Concentric
  data centers. A closed community group has access to the multicast
  information, which consists of live races, track calls, live odds, past
  performance, secured wagering from a pari-mutuel escrow account and
  handicap information. Concentric believes it was chosen as the network
  provider by You Bet! because of its expertise in developing back-end
  systems and its ability to deploy and manage a virtual private network.
  Concentric will collect hourly usage fees from You Bet!
 
    PictureTel Corporation. PictureTel Corporation ("PictureTel"), a leading
  provider of video conferencing products, and Concentric have signed a
  Letter of Agreement which specifies both parties' intent to negotiate final
  agreements concerning a business relationship regarding plans to enable
  PictureTel desktop and room video conferencing systems to communicate over
  the Concentric network. Both Concentric and PictureTel currently have trial
  systems installed and operating over the Concentric network. Preliminary
  results demonstrate that the low/fixed latency and high throughput of the
  Concentric network delivers superior quality for both desktop and room
  video conferencing over IP-routed networks.
 
THE CONCENTRIC NETWORK
 
  The Concentric network employs an advanced, geographically dispersed ATM and
frame relay backbone, 14 SuperPOPs in many major metropolitan areas plus a
total of 132 secondary and tertiary POPs in other cities, allowing
 
                                      41
<PAGE>
 
local dial-up access to the network to users in the U.S. and Canada. In
addition, the Company can provide analog dial-up, frame relay, fractional T-1,
T-1 and DS3 access to the network. The Concentric network currently supports
28.8 Kbps (V.34) modems and is evaluating plans to upgrade to 56.6 Kbps modem
access. The Concentric network is managed via a centralized network control
center in St. Louis, Missouri. Two data centers (located in Bay City, Michigan
and Cupertino, California) house the servers that support
logon/authentication, billing, e-mail, Internet access, Web services and other
network services.
 
  The Concentric SuperPOPs are designed to support both dial-up and dedicated
access services within a broad geographic region. Typically, a SuperPOP will
utilize one or more CLECs and LECs to aggregate dial traffic within a 50-200
mile radius of the SuperPOP and terminate it at the SuperPOP. This strategy
allows Concentric to offer users local call coverage within the SuperPOP
region without having to deploy individual POPs in each local calling area.
All the calls are terminated at the modem equipment at the regional SuperPOP.
This results in broader call coverage, lower costs due to the typically lower
rates from CLECs and economies of scale from larger modem installations, lower
maintenance costs, and easier capacity upgrades since equipment is located in
a single location within a region.
 
  DAFs from customer locations in a region are terminated in the SuperPOP as
well. Typically, Fractional T-1, T-1, and T-3 circuits are terminated directly
into SuperPOP router equipment (via CSU/DSUs). Frame access is terminated via
aggregated LEC Frame Access circuit(s). Both dial and dedicated traffic is
then aggregated by the routers/switches in the SuperPOP and directed to the
Concentric ATM backbone via one or more T-3 ATM links.
 
  Traditional network designs allocate dedicated network resources to specific
classes of applications. For example, separate network resources (or networks)
might be dedicated to transaction processing applications versus Internet
applications. Concentric believes that a major advantage of its network
architecture is the ability of the network to support adaptive call processing
("ACP"). ACP is designed to allow a common set of network resources to be used
for different applications on a call-by-call basis. Performance and
functionality for the user is improved, because each end-user receives the
needed services on a customized basis instead of relying on a "one-size-fits-
all" network approach. Furthermore, the Company believes that ACP will reduce
costs by making it possible to optimize network usage on a call-by-call basis
to provide only the services actually needed. Using software implemented by
Bay Networks, Inc. in accordance with Concentric specifications, ACP is
designed to enable the tuning of network parameters and traffic routing to
meet the level of latency, throughput, security/privacy, and reliability
requirements of a specific customer or application on a call-by-call basis.
The initial release of ACP will utilize the phone number dialed by the
subscriber to determine the configuration parameters and protocol support
required by the access modems and communications servers. Concentric is
currently deploying the software technology in its network and is planning to
commercially introduce the initial ACP capabilities during the second half of
1997.
 
  Some applications, such as Web browsing and file transfer require high
throughput, but can tolerate moderate and variable latency, while others, such
as mission-critical business applications, multiplayer gaming and voice and
video conferencing, require low/fixed latency. Still others, such as
transaction processing, require fast connect/disconnect times, may require
high levels of security and are indifferent to latency levels. Traditional
static network access technologies and backbone architectures cannot cost-
effectively manage these varied requirements in a single network. The
Concentric network has been designed to be able to solve this problem by
incorporating software intelligence in both its access and backbone
technologies to adapt the network's connection setup and data transfer
properties to the nature of the user's application requirements on a call-by-
call or service-by-service basis.
 
  The Concentric network also offers its customers the security, reliability
and management features that companies require in their own private networks.
Varying layers of security and encryption are supported and tailored to
specific customer requirements. The network design includes a standard
security layer and is compatible with most types of custom security
applications. Further, security is provided at both the edge of the network
and internally based on embedded firewall and encryption techniques. The
Concentric network features co-location of network access and switching
equipment in "hardened" facilities, direct connections to carrier facilities,
a resilient ATM/frame relay backbone, dual data processing centers, and
redundancy within data centers to substantially enhance its uptime
performance.
 
                                      42
<PAGE>
 
  Network managers, customer service, and technical support staff require near
real-time access to information about the performance and quality of their
networks. In traditional private networks, this information is provided by
network management, trouble reporting/tracking, and management information
systems. Customers usually sacrifice a great deal of control and have access
to less information when using a public network instead of a private network.
It has been difficult for public network providers to provide their major
customers with information regarding network performance that relates to that
customer's usage without either compromising other customers' proprietary
information or compromising the integrity of the network itself. Concentric
has developed a set of non-intrusive software tools and reporting mechanisms,
distributed to DAF enterprise customers as ConcentricView. ConcentricView
allows a customer's network manager to monitor network performance and quality
and to adequately support inquiries for help from their users. Web browsers
and file transfer tools are used to provide access to much of this
information. In some cases, custom integration of Concentric's network
management and trouble tracking/reporting systems will be provided to
customers.
 
SALES AND MARKETING
 
  The Company focuses on marketing its services to two distinct market
segments: enterprise and consumer. By attracting enterprise customers who use
the network primarily during the daytime, and consumer customers who use the
network primarily at night, the Company is able to more fully utilize its
network infrastructure by having some customers online during the day and the
others, using the same modem pools, online during the evening. The Company has
developed a multi-tiered sales strategy consisting of leveraged third party
distribution channels, inbound and outbound telesales, value-added resellers
and direct sales.
 
  Leveraged Third Party Distribution. The Company has positioned itself as a
key network services provider for companies that bundle network access in
their products or services. For example, the Company's network service is
bundled with Intuit's Quicken, TurboTax and Quickbooks products, Microsoft
Office 97 and with WebTV and Sega Saturn Internet access devices.
Additionally, the Company is one of the Internet services providers listed on
the Netscape Navigator and Microsoft Internet Explorer browser registration
servers.
 
  Telesales. The Company uses an inbound telesales group to answer calls from
potential consumers/subscribers and to sign up customers. Inbound telesales
representatives also proactively upsell premium products and services. The
Company also uses an outbound telesales group to sell DAFs and high-end
hosting products to small and medium-sized businesses. Both the inbound and
outbound telesales groups forward leads to the direct sales force when
appropriate.
 
  Value-Added Resellers. The Company has also begun to establish sales
channels through value-added resellers. These resellers are companies that
sell equipment or other components for full-service network solutions to
medium and large businesses. Value-added resellers such as Racal-Datacom,
Inc., which employs more than 500 direct sales, sales-support and network
services people, are compensated for selling Concentric's enterprise service
offerings in conjunction with their other products. These relationships enable
the VARs to provide more comprehensive solutions to their customers while
affording the Company the benefit of the VAR's large sales force without
incurring the costs of maintaining a large sales force of its own.
 
  Direct Sales Force. For large and complex enterprise solutions and to
acquire, support and retain distribution channel partners, the Company employs
11 direct sales people located in Cupertino and Orange County, California,
Dallas, Texas, and the New York metropolitan area to provide national direct
sales coverage. The Company's direct sales force is supported by inside
sales/account managers and systems engineers.
 
  Concentric markets its enterprise services to information service ("IS")
professionals. In addition, the Company uses print advertising in targeted
industry publications to build awareness and acquire leads for its VARs and
its direct sales team. The Company is also planning to launch in the second
half of 1997 a large direct response effort (direct mail/outbound
telemarketing) targeting enterprise IS managers and senior management of
multilocation companies, and companies with large numbers of mobile and
telecommuting employees.
 
 
                                      43
<PAGE>
 
  In the consumer market, the Company focuses on direct mail to targeted
audiences; establishment of customer referral programs; and co-marketing such
as packaging literature with MasterCard mailers and Intuit software. In
addition, the Company has implemented on-line programs, such as a Website
"home" where they can learn how to use the service, how to use the Internet,
and how to find information quickly, designed to increase customer retention.
The Company is also implementing programs to sell additional products and
services to its consumer customers. Additionally, the Company is generating
advertising revenue on its growing Website traffic in direct ad banner
placements as well as in shared revenue relationships with content partners
such as Excite, Inc., Lycos, Inc., and Classifieds2000, Inc.
 
  The Company employs public relations personnel in-house and works with an
outside public relations agency to provide broad coverage in network computer
and vertical industry publications. The Company participates in industry trade
shows based on the size and vertical makeup of the trade show audience.
Planned shows in 1997 include E3 and NetWorld + InterOp. The Company also
participates in trade shows with its strategic marketing partners such as
Racal-Datacom to promote the sale of Concentric products and services.
 
  As of March 31, 1997, the Company employed 63 persons in sales and
marketing. The Company is in the process of expanding its sales and marketing
staff. The Company's sales operations are conducted from its principal office
in Cupertino, California and by its field sales personnel in Orange County,
California, Dallas, Texas and the New York metropolitan area.
 
CUSTOMER SUPPORT
 
  Concentric believes that a high level of customer support is critical to
attracting and retaining its enterprise and consumer customers. The Company
maintains a customer support call center at its Saginaw, Michigan, facility.
Concentric offers several levels of customer support all of which are
available 24 hours per day, seven days per week. The basic level of customer
support includes support for customers on installing and using their software,
customer communications and customer training. Premier level service programs
guarantee an exceptional performance standard, offer supplemental support
training, and provide monthly reports on operations. Private label support
gives businesses a premier level of support provided by their own customer
service team who answer calls with that customer's company name. Customer
support is provided by e-mail, telephone, Website and online chat.
 
  As of March 31, 1997, the Company employed 142 persons in customer support.
In addition, the Company outsources supplemental customer support to
Concentric customers and their end-users.
 
COMPETITION
 
  The market for tailored value-added network services is extremely
competitive. There are no substantial barriers to entry, and the Company
expects that competition will intensify in the future. The Company believes
that its ability to compete successfully depends upon a number of factors,
including market presence; the capacity, reliability, low latency and security
of network infrastructure; technical expertise and functionality, performance
and quality of services; customization; ease of access to and navigation of
the Internet; the pricing policies of its competitors; the variety of
services; the timing of introductions of new services by the Company and its
competitors; customer support; the Company's ability to support industry
standards; and industry and general economic trends.
 
  The Company's current and prospective competitors generally may be divided
into the following five groups: (i) telecommunications companies, such as
AT&T, MCI, Sprint, Inc., WorldCom, RBOCs and various cable companies; (ii)
online services providers, such as America Online, CompuServe, Microsoft's
MSN, and Prodigy; (iii) ISPs, such as BBN, NETCOM, PSI, and other national and
regional providers; (iv) nonprofit or education Internet connectivity
providers; and (v) Web server farms such as Internet Direct and Exodus. Many
of these competitors have greater market presence, engineering and marketing
capabilities, and financial, technological and personnel resources than those
available to the Company. As a result, they may be able to develop and expand
their communications and network infrastructures more quickly, adapt more
swiftly to new or emerging technologies and changes in customer requirements,
take advantage of acquisition and other opportunities more readily, and devote
 
                                      44
<PAGE>
 
greater resources to the marketing and sale of their products than can the
Company. In addition, various organizations, including certain of those
identified above, have entered into or are forming joint ventures or
consortiums to provide services similar to those of the Company.
 
  The Company believes that new competitors, including large computer
hardware, software, media and other technology and telecommunications
companies will enter the value added network services markets, resulting in
even greater competition for the Company. Certain of such telecommunications
companies and online services providers are currently offering or have
announced plans to offer Internet or online services or to expand their
Internet access services. Certain companies, including America Online, BBN and
PSI, have also obtained or expanded their Internet access products and
services as a result of acquisitions. Such acquisitions may permit the
Company's competitors to devote greater resources to the development and
marketing of new competitive products and services and the marketing of
existing competitive products and services. In addition, the ability of some
of the Company's competitors to bundle other services and products with VPN
and consumer network services could place the Company at a competitive
disadvantage. Certain companies are also exploring the possibility of
providing high-speed data services using alternative delivery methods such as
over the cable television infrastructure, through direct broadcast satellite
technology and by wireless cable.
 
  The Company may apply for licenses to become a CLEC in selected states. To
the extent the Company obtains such licenses and commences CLEC operations, it
will compete with the incumbent LEC and additional CLECS providing
telecommunications services in these markets. For all new entrants, including
the Company, the market for local exchange services is extremely competitive.
Local telecommunications services offered by the Company will compete
principally with services offered by the incumbent LEC serving that area.
Incumbent LECs, such as the RBOCs, currently dominate their local telephone
markets. Such companies have financial, managerial and technical resources
that substantially exceed those of the Company and have long-standing
relationships with their customers. While the 1996 Telecom Act provides
increased business opportunities to CLECs, it also allows incumbent LECs
increased pricing flexibility for their services. Increased price competition
from incumbent LECs could have a material adverse effect on the Company's CLEC
operations and, in turn, on the Company's results of operations and financial
condition to the extent its CLEC operations are a material portion of its
business. Furthermore, upon the satisfaction of certain regulatory conditions,
the RBOCs currently are expected to be able to offer long distance services in
their home markets in addition to local service, which would afford their
local customers "one-stop shopping" for telecommunications services. The
Company also expects to face increased competition in the provision of local
exchange services from other CLECs, cable television companies, electric
utilities, microwave carriers, wireless telephone system operators, AT&T, MCI,
Sprint, WorldCom and other long distance carriers who may choose to enter the
local exchange market by resale of incumbent LEC facilities.
 
  As a result of increased competition in the industry and vertical and
horizontal integration in the industry, the Company could encounter
significant pricing pressure, which in turn could result in significant
reductions in the average selling price of the Company's services. For
example, certain of the Company's competitors that are telecommunications
companies may be able to provide customers with reduced communications costs
in connection with their Internet access services or private network services,
reducing the overall cost of their solutions and significantly increasing
price pressures on the Company. There can be no assurance that the Company
will be able to offset the effects of any such price reductions with an
increase in the number of its customers, higher revenue from enhanced
services, cost reductions or otherwise. In addition, the Company believes that
the Internet access and online services businesses are likely to encounter
consolidation in the near future, which could result in increased price and
other competition in these industries and, potentially, the virtual private
networks industry. Increased price or other competition could result in
erosion of the Company's market share and could have a material adverse effect
on the Company's business, financial condition and results of operations.
There can be no assurance that the Company will have the financial resources,
technical expertise or marketing and support capabilities to continue to
compete successfully. See "Risk Factors--Competition," "--Risks of Growth and
Expansion" and "--Future Capital Needs; Uncertainty of Additional Financing"
and "Business--Competition."
 
                                      45
<PAGE>
 
GOVERNMENT REGULATION
 
  Value-Added Network and Internet Service Providers. The FCC currently does
not regulate value-added network software or computer equipment related
services that transport data or voice messages over telecommunication
facilities. The Company provides value-added IP-based network services, in
part, through data transmissions over public telephone lines. These
transmissions are governed by regulatory policies establishing charges and
terms for wireline communications. Operators of these types of value-added
networks that provide access to regulated transmission facilities only as part
of a data services package are currently excluded from regulations that
applies to "telecommunications carrier" and as such the Company is not
currently subject to direct regulation by the FCC or any other governmental
agency, other than regulations applicable to businesses generally. However, in
the future the Company could become subject to regulation by the FCC or
another regulatory agency as a provider of basic telecommunications services.
 
  Currently, the FCC is reviewing its regulatory positions and could seek to
impose common carrier regulation on the network transport and communications
facilities aspects of an enhanced or information service package. Further, the
FCC could conclude that the Company's protocol conversions, computer
processing, and interaction with customer-supplied information are
insufficient to afford the Company the benefits of the enhanced or information
service classification, and thereby may seek to regulate some segments of the
Company's activities as basic telecommunications services. While state public
utility commissions generally have declined to regulate enhanced or
information services, some states have continued to regulate particular
aspects of enhanced services in limited circumstances, such as where they are
provided by LECs. Moreover, the public service commissions of certain states
continue to review potential regulation of such services. There can be no
assurance that regulatory authorities of states within which Concentric makes
its Internet access, Intranet and VPN services available will not seek to
regulate aspects of these activities as telecommunications services. Changes
in the regulatory environment relating to the Internet connectivity market,
including regulatory changes that directly or indirectly affect
telecommunications costs or increase the likelihood or scope of competition
from the RBOCs or other telecommunications companies, could affect the prices
at which the Company may sell its services. The Company cannot predict the
impact, if any, that future regulation or regulatory changes may have on its
business and there can be no assurance that such future regulation or
regulatory changes will not have a material adverse effect on the Company's
business, results of operations and financial condition.
 
  Competitive Local Exchange Carriers. The Company may apply for certificates
of authority to become a CLEC in selected states. To the extent the Company
obtains such authorizations and commences CLEC operations, the
telecommunications services provided by such operations will be subject to
regulation by federal, state and local governmental agencies. At the federal
level, the FCC has jurisdiction over interstate telecommunications services.
State regulatory commissions exercise jurisdiction over intrastate services.
Additionally, municipalities and other local government agencies may regulate
limited aspects of the Company's business, such as use of rights-of-way.
Typically start-up telecommunications carriers are not as heavily regulated as
incumbent LECs. For example, under current regulations, the Company would not
be subject to price cap or rate of return regulation by the FCC. However, the
Telecommunications Act of 1996 (the "1996 Telecom Act") requires the FCC to
establish a subsidy mechanism for universal telephone service to which the
Company will be required to contribute based on its telecommunications
revenues and requires all LECs, including CLECs, to make services available
for resale by other carriers, provide nondiscriminatory access to rights-of-
way, offer reciprocal compensation for termination of local telecommunication
traffic and provide dialing parity and telephone number portability, and
ensure that their services are accessible to and usable by persons with
disabilities. The 1996 Telecom Act retains for individual states the authority
to impose their own regulations of local exchange services, including state
universal service subsidy programs, so long as this regulation is not
inconsistent with the requirements of the 1996 Telecom Act. The Company is
unable to predict the final form of such regulation and its potential impact
on the Company. In its provision of interstate, international and intrastate
services as a CLEC, the Company generally will be subject to tariff filing
requirements setting forth the terms, conditions and prices for services,
prior to offering telecommunications services. At the state level, the Company
will also be subject to state certification proceedings as a CLEC. These
certifications generally require a showing that the carrier has adequate
financial, managerial and technical resources to offer the proposed services
consistent with the public interest. Under some state statutes changes in the
ownership of the Company's outstanding
 
                                      46
<PAGE>
 
voting securities also may trigger additional state public utility commission
approval. For example, in certain jurisdictions an investor who acquires as
little as ten percent or more of the Company's voting securities may have to
obtain prior approval of the acquisition of such securities because such
ownership might be deemed to constitute an indirect controlling interest in
the CLEC. While uncommon, challenges to these tariffs and certificates by
third parties could cause the Company to incur substantial legal and
administrative expenses. Many states also have additional regulatory
requirements such as minimum service quality reporting and customer service
requirements and uniform LEC accounting requirements.
 
  Although the 1996 Telecom Act eliminates legal barriers to entry into the
CLEC market, no assurance can be given that changes in current or future
regulations adopted by the FCC or state regulators or other legislative or
judicial initiatives relating to the telecommunications industry would not
have a material adverse effect on the Company's ability to offer such
services. With the passage of the 1996 Telecom Act and the anticipated
increase in the level of competition faced by incumbent LECs, the FCC could
grant incumbent LECs substantial pricing flexibility with regard to interstate
access services. It is also anticipated that the prices incumbent LECs charge
for access services will be substantially reduced as a result of the FCC's
reform of the current access charge regime and the adoption of universal
service rules. Similarly, a number of states have allowed incumbent LECs rate
and tariff flexibility, particularly for services deemed subject to
competition. Such price competition could significantly and adversely affect
the Company's CLEC operations which could, in turn, adversely affect the
Company's results of operations and financial condition to the extent its CLEC
operations are a material portion of its business.
 
PROPRIETARY RIGHTS
 
  The Company's success and ability to compete is dependent in part upon its
technology, although the Company believes that its success is more dependent
upon its technical expertise than its proprietary rights. The Company
principally relies upon a combination of copyright, trademark and trade secret
laws and contractual restrictions to protect its proprietary technology. It
may be possible for a third party to copy or otherwise obtain and use the
Company's products or technology without authorization or to develop similar
technology independently, and there can be no assurance that such measures
have been, or will be, adequate to protect the Company's proprietary
technology or that the Company's competitors will not independently develop
technologies that are substantially equivalent or superior to the Company's
technology. The Company operates a material portion of its business over the
Internet, which is subject to a variety of risks. Such risks include but are
not limited to the substantial uncertainties that exist regarding the system
for assigning domain names and the status of private rules for resolution of
disputes regarding rights to domain names. There can be no assurance that the
Company will continue to be able to employ its current domain names in the
future or that the loss of rights to one or more domain names will not have a
material adverse effect on the Company's business and results of operations.
 
  Although the Company does not believe that it infringes the proprietary
rights of any third parties, there can be no assurance that third parties will
not assert such claims against the Company in the future or that such claims
will not be successful. In addition, participants in the Company's industry
also rely upon trade secret law. The Company could incur substantial costs and
diversion of management resources with respect to the defense of any claims
relating to proprietary rights which could have a material adverse effect on
the Company's business, financial condition and results of operations.
Furthermore, parties making such claims could secure a judgment awarding
substantial damages, as well as injunctive or other equitable relief which
could effectively block the Company's ability to license its products in the
United States or abroad. Such a judgment would have a material adverse effect
on the Company's business, financial condition and results of operations. In
addition, the Company is obligated under certain agreements to indemnify the
other party in connection with infringement by the Company of the proprietary
rights of third parties. In the event a claim relating to proprietary
technology or information is asserted against the Company, the Company may
seek licenses to such intellectual property. There can be no assurance,
however, that licenses could be obtained on commercially reasonable terms, if
at all, or that the terms of any offered licenses will be acceptable to the
Company. The failure to obtain the necessary licenses or other rights could
have a material adverse effect on the Company's business, financial condition
and results of operations.
 
 
                                      47
<PAGE>
 
EMPLOYEES
 
  As of March 31, 1997, Concentric had 280 employees and 48 independent
contractors, including 63 persons in sales and marketing, 91 persons in
network operations and development, 142 in customer support and 32 in finance
and administrative functions. The Company believes that its future success
will depend in part on its continued ability to attract, hire and retain
qualified personnel. Competition for such personnel is intense, and there can
be no assurance that the Company will be able to identify, attract, and retain
such personnel in the future. None of the Company's employees is represented
by a labor union, and management believes its employee relations are good.
 
PROPERTIES
 
  The Company's executive offices are located in Cupertino, California, under
a lease that expires in April 1998. The Company also leases network operations
and customer support facilities in Bay City, Michigan, and Saginaw, Michigan,
respectively, under leases expiring in December 1997 and December 2001,
respectively. The Saginaw lease obligates the Company to pay up to $1.25
million to restore the building in the event of any damage or destruction to
it during the lease term, without any rent abatement for loss of use. The
Company believes that its existing facilities are adequate for its current
needs.
 
LEGAL PROCEEDINGS
 
  On April 22, 1997, a complaint was filed in the Los Angeles County,
California Superior Court against the Company and other unnamed defendants by
Sattel Communications LLC ("Sattel"). The complaint alleges claims for breach
of contract, breach of the covenant of good faith and fair dealing, unfair
business practices, fraud and negligent misrepresentation. Sattel claims that
the Company is in breach of an agreement to pay for up to $4.3 million of DSS
Switches from Sattel for use in the Company's network. The Complaint also
seeks unspecified consequential and punitive damages. On April 29, 1997,
Sattel served the Company with an Application for Writ of Attachment, seeking
to secure a lien on the Company's assets up to an amount of $3.6 million. At a
hearing held on June 25, 1997, the Court granted the writ. On July 11, 1997,
the Company entered into a Settlement Agreement and Mutual Release with Sattel
regarding the lawsuit (the "Settlement Agreement"). Pursuant to the Settlement
Agreement, the Company agreed to pay Sattel $4,400,000 for products that the
Company had purchased and received from Sattel, with such amount to be paid on
or before August 15, 1997. The Company also agreed to purchase, at the
election of Sattel, up to 25% of the Company's stock currently held by Sattel
on the day after the closing of the offering made hereby at the initial Price
to the Public per share. As part of the settlement, the Company and Sattel
agreed to release each other from any claims they might have against the
other, and Sattel expressly released the Company from any further obligation
the Company might have to purchase additional equipment from Sattel. The
Company had previously reserved $5.8 million for the Sattel litigation to
account for the possible outcomes of the litigation.
 
  In late April and early May, 1997, three putative securities class action
complaints were filed in the United States District Court, Central District by
certain stockholders of Diana Corporation ("Diana"), the parent corporation of
Sattel, alleging securities fraud related to plaintiffs' purchase of shares of
Diana Common Stock in reliance upon allegedly misleading statements made by
defendants, Diana, Sattel and certain of their respective affiliates, officers
and directors. Concentric was named as a defendant in the complaint in
connection with certain statements made by Diana and officers of Diana related
to Concentric's purchase of network switching equipment from Diana's Sattel
subsidiary. The complaints do not appear to allege that Concentric made any
false or misleading statements. The plaintiffs seek unspecified compensatory
damages.
 
  While the ultimate outcome of such litigation is uncertain, the Company
believes it has meritorious defenses to the claims and intends to conduct
vigorous defenses. An unfavorable outcome in these matters could have a
material adverse effect on the Company's financial condition. In addition,
even if the ultimate outcomes are resolved in favor of the Company, the
defense of such litigation could entail considerable cost and the diversion of
efforts of management, either or which could have a material adverse effect on
the Company's results of operations. See "Risk Factors--Legal Proceedings" and
Note 10 of Notes to Financial Statements.
 
                                      48
<PAGE>
 
                                  MANAGEMENT
 
EXECUTIVE OFFICERS, DIRECTORS AND SENIOR MANAGEMENT
 
  The following table sets forth certain information as of March 31, 1997,
with respect to the executive officers and directors of the Company, as well
as certain members of its senior management.
 
<TABLE>
<CAPTION>
      NAME                        AGE                  POSITION
  -----------------------------------------------------------------------------
   <S>                            <C> <C>
   Henry R. Nothhaft.............  52 President, Chief Executive Officer and
                                      Director
   John K. Peters................  49 Executive Vice President and General
                                      Manager, Network Services Division
   Michael F. Anthofer...........  45 Senior Vice President and Chief Financial
                                      Officer
   William C. Etheredge..........  50 Senior Vice President of Sales
   George D. Carr................  52 Vice President of Field Sales
   Eileen A. Curtis..............  48 Vice President of Customer Relations
   Scott G. Eagle................  38 Vice President of Consumer Marketing
   Donald C. Schutt..............  51 Vice President of Michigan Operations
   Warren A. Smith...............  46 Vice President of Software Engineering
   James L. Isaacs...............  37 Vice President of Product Management
   Mark W. Fisher................  36 Vice President of Corporate Marketing
   Louis P. Bender, III(1).......  50 Director
   Robert W. Doede(1)............  57 Director
   Vinod Khosla(2)...............  42 Director
   Randy A. Maslow...............  42 Director
   Terence M. O'Toole............  38 Director
   Franco Regis(1)...............  41 Director
   Gary E. Rieschel(2)...........  41 Director
</TABLE>
- --------
(1) Member of the Audit Committee.
(2) Member of the Compensation Committee.
 
  Henry R. Nothhaft joined the Company as President and Chief Executive
Officer in May 1995 and became a Director of the Company in August 1995. From
1989 to August 1994, Mr. Nothhaft was President, Chief Executive Officer and a
Director of David Systems, Inc. ("David Systems"), a networking company. From
1983 to 1989, Mr. Nothhaft held various positions with DSC Communications
Corporation ("DSC"), including Senior Vice President of Marketing, President
of the Digital Switch Corporation subsidiary, President of the Business
Network Systems Group and a Corporate Director of DSC. From 1979 to 1983, Mr.
Nothhaft was Vice President of Domestic Marketing and Vice President of Sales
for GTE Telenet Communications Corporation (now Sprint). Mr. Nothhaft has an
M.B.A. in Information Systems Technology from George Washington University and
a B.S. degree from the U.S. Naval Academy.
 
  John K. Peters joined the Company in May 1995 as an independent consultant.
Mr. Peters was named Executive Vice President and General Manager, Network
Services Division of the Company in June 1995. From 1993 to August 1995, Mr.
Peters served as President of Venture Development Consulting, a consulting
firm specializing in new communications, information services and software
businesses. From 1988 to 1993, Mr. Peters was Vice President and Chief
Operating Officer of Pacific Bell Information Services, Inc. Prior to that,
Mr. Peters spent three years as Vice President of Application Services for
Telestream Corporation. In 1981, Mr. Peters co-founded Integrated Office
Systems, Inc., a communications and information systems company. From 1976 to
1980, Mr. Peters was Vice President of Advanced Network Services for GTE
Telenet Communications Corporation. Mr. Peters has an M.B.A. from Stanford
Graduate School of Business and a B.S. degree in Statistics from Stanford
University.
 
  Michael F. Anthofer joined the Company in January 1996 as Vice President and
Chief Financial Officer and became a Senior Vice President in November 1996.
From January 1991 to December 1995, Mr. Anthofer served as an Executive Vice
President and Chief Financial Officer of Shared Resource Exchange, Inc., a
privately held digital
 
                                      49
<PAGE>
 
switching platform and PBX supplier. Prior to 1991, Mr. Anthofer held various
executive positions, including Vice President, Corporate Business Planning,
Vice President, Business Network Group and Vice President, Network Products
Group, at DSC. Mr. Anthofer has an M.B.A. and a B.S. degree from the
University of California, Berkeley.
 
  William C. Etheredge joined the Company in March 1997 as the Senior Vice
President of Sales. From May 1991 to March 1997, Mr. Etheredge served first as
Vice President of Sales and Marketing and then as Vice President of Sales for
Meridian Data, Inc., a provider of networked CD-ROM database creation and
retrieval software and network servers. From July 1990 to May 1991, he served
as Vice President of Strategic Accounts for Maxtor Corporation. From June 1985
to June 1990, he served first as Vice President US Sales and Marketing and
then Vice President Western Region for Memorex-Telex Corporation. Mr.
Etheredge has an M.B.A. degree from Bowling Green University and a B.A. degree
from Westminster College.
 
  George D. Carr joined the Company in June 1995 as an independent consultant.
In September 1995 Mr. Carr became Vice President of Sales. From June 1993 to
June 1995, Mr. Carr was Vice President of Sales and Marketing of David
Systems/ChipCom. From June 1989 to June 1993, Mr. Carr was VP of Operations
and International Sales of David Systems. From December 1983 to June 1989, Mr.
Carr was VP of Operations and Service of David Systems. Mr. Carr has a B.A.
degree from Loyola Marymount.
 
  Eileen A. Curtis joined the Company in November 1994 as an independent
consultant. She became Customer Relations Manager in January 1995, Director of
Customer Relations in September 1995 and Vice President, Customer Relations in
November 1996. From August 1987 to July 1993, Ms. Curtis was employed by Cox
Communications Saginaw, Inc. and served in various positions including
Marketing and Public Relations Manager, Administrative Manager and Customer
Service Manager. Ms. Curtis has a B.S. degree from Central Michigan
University.
 
  Scott G. Eagle joined the Company in March 1996 as Vice President of
Consumer Marketing. From November 1993 to February 1996, Mr. Eagle was the
Vice President, Strategic Marketing Development for MFS Intelenet, Inc., a
start-up division of MFS Communications Company, Inc. From February 1989 to
November 1993, Mr. Eagle was the Vice President of Marketing for the
Woodbridge Group, a marketer of consumer package goods. Prior to February
1989, Mr. Eagle served in various marketing management positions with The
Procter & Gamble Company. Mr. Eagle has a B.S. degree from the University of
Pennsylvania, Wharton School of Business.
 
  Donald C. Schutt joined the Company in February 1994 as Vice President of
Sales and Marketing and was appointed Chief Operations Officer later that
year. Mr. Schutt was named Vice President and General Manager, Bay City
Operations in August 1995. His title was changed to Vice President of Michigan
Operations in March 1996. From 1964 to 1985, Mr. Schutt held various
management positions with General Motors, after which Mr. Schutt served until
1989 as Vice President for Sales and Marketing for Gentex Corporation. From
1989 to 1993, Mr. Schutt was President and Chief Executive Officer of AMPM,
Inc., a full-service advertising agency, and retains a 54 percent interest in
such entity. Mr. Schutt has a B.S. degree in Marketing from Ferris University.
 
  Warren A. Smith joined the Company in April 1996 as Vice President, Software
Engineering. From October 1992 to April 1996, Mr. Smith was the Director of
Engineering at NetManage, Inc., a software company. From July 1987 to July
1992, Mr. Smith was the Director of Distributed Computing Technology for Sun
Microsystems, Inc. From March 1983 to July 1987, Mr. Smith was the Western
Regional Manager of SEI Information Technology an engineering consulting firm.
Mr. Smith has a B.S. degree from California State University, Sacramento.
 
  James L. Isaacs joined the Company in October 1995 as the Director of
Product Management. In March 1997, he became Vice President of Product
Management. From July 1988 to October 1995, Mr. Isaacs held various positions
at Apple Computer, including Group Manager Product Marketing, Apple On Line
Services Division and Business Development Manager of Apple On Line Services
Division. Mr. Isaacs has an M.B.A. degree from the University of California,
Berkeley and an A.B. degree from Stanford University.
 
  Mark W. Fisher joined the Company in June 1997 as Vice President of
Corporate Marketing. From July 1996 to June 1997, Mr. Fisher was General
Manager and Vice President, Marketing of Pacific Bell Internet Services, a
wholly
 
                                      50
<PAGE>
 
owned subsidiary of Pacific Bell. From June 1995 to August 1996, Mr. Fisher
was Vice President, Marketing of Pacific Bell Internet Services. From 1989 to
May 1995, Mr. Fisher held various data product marketing and data center
operations positions at Pacific Bell. Mr. Fisher has an M.B.A. from the
University of California at Berkeley and a B.S. in mechanical engineering from
the U.S. Naval Academy.
 
  Louis P. Bender, III has been a Director of the Company since June, 1997.
Since November 1996 he has been President, Americas Region of Racal Data
Group. Prior to such time, Mr. Bender served as Vice President, Business
Development at Bull Electronics, a business unit of Group Bull in Angers,
France. Prior to Bull Electronics, Mr. Bender held the position of Vice
President, Worldwide Sales at AVEX Electronics. Mr. Bender has bachelor's
degrees in Electrical Engineering and Business Administration from the State
University of New York and Monroe College, respectively.
 
  Robert W. Doede has been a Director of the Company since June 1997. Mr.
Doede is chairman of FundMinder Inc., an investment advisory firm, and has
served in that position since December 1991. He holds a B.A. degree from Yale
College and a doctorate of economics from the University of Chicago.
 
  Vinod Khosla has been a Director of the Company since April 1995. Mr. Khosla
has been a General Partner with the venture capital firm of Kleiner Perkins
Caufield & Byers from February 1986 to the present. Mr. Khosla was a co-
founder of Daisy Systems and the founding Chief Executive Officer of Sun
Microsystems, Inc. Mr. Khosla also serves on the boards of Excite, Inc.,
PictureTel, The 3DO Company, and Spectrum Holobyte. He has a B.S.E. from the
Indian Institute of Technology in New Delhi, an M.S.E. from Carnegie Mellon
University, and an M.B.A. from the Stanford Graduate School of Business.
 
  Randy A. Maslow joined the Company in March 1994 as an independent
consultant and subsequently served as Vice President for Business Development
from September 1994 through February 1996. He has been a director of the
Company since January 1995. Since February 1996, Mr. Maslow has been Managing
Director of Electric Ventures, Inc., a venture finance firm in the interactive
services industry. Prior to joining Concentric, Mr. Maslow was a co-founder
and managing partner of the RAM Group, a venture finance and business
development consulting firm in the online services and electronic publishing
industries. From 1982 through 1989, Mr. Maslow was a corporate attorney in
private practice. Mr. Maslow has a B.A. degree from Cornell University and a
J.D. from Rutgers Law School.
 
  Terence M. O'Toole has been a Director of the Company since April 1995. Mr.
O'Toole is a Managing Director at Goldman, Sachs & Co. Mr. O'Toole joined
Goldman, Sachs & Co. in 1983, became a general partner in 1992 and a Managing
Director in 1996. Mr. O'Toole serves on the boards of directors of AMF Group,
Inc., Insilco Corporation, and Western Wireless Corporation. He has a B.S.
degree from Villanova University and an M.B.A. from the Stanford University
Graduate School of Business.
 
  Franco Regis has been a Director of the Company since October 1996. Since
1994, Mr. Regis has been a Director of Business Development and Strategic
Planning at Telecom Italia, SpA, the telephone operating company of Italy.
From 1992 to 1994, Mr. Regis was a Director of Budget and Control for the
business division of Telecom Italia. Mr. Regis has an engineering degree from
the Rome State University.
 
  Gary E. Rieschel has been a Director of the Company since October 1996. Mr.
Rieschel is a Senior Vice President at SOFTBANK Holdings, having joined that
company in January 1996. Mr. Rieschel was Vice President for N-Cube
Corporation from August 1994 through December 1995. He was Sales Director at
Cisco Systems, Inc. from July 1993 through October 1994. Prior to this, Mr.
Rieschel was a General Manager and Sales Director at Sequent Computer for over
nine years. Mr. Rieschel has an M.B.A. from Harvard Graduate School of
Business and a B.A. in biology from Reed College.
 
  Members of the Board of Directors are elected each year at the Company's
annual meeting of stockholders, and serve until the following annual meeting
of stockholders and until their respective successors have been elected and
qualified.
 
                                      51
<PAGE>
 
 Voting Agreements
 
  Pursuant to a Stockholder Agreement entered into in connection with the
Company's sale of Series A Preferred Stock, as amended and restated in
connection with the issuance of Series B Preferred Stock and Series B
warrants, each of Kleiner Perkins Caufield & Byers VII, KPCB VII Founders Fund
and KPCB Information Sciences Zaibatsu Fund II (collectively, the "Kleiner
Entities"), Mr. Collins-Rector, Mr. Chad Shackley, Intuit and GS Capital
Partners, L.P. ("GSCP") has agreed to vote all its capital stock, except for
any Series B Preferred Stock, to elect as directors the Chief Executive
Officer of the Company and two other individuals designated by GSCP and the
Kleiner Entities. This voting obligation terminates as to each such
stockholder upon the earlier of (i) such stockholder no longer beneficially
owning any shares of Stock, as defined in such Stockholder Agreement, and (ii)
the closing of a public offering resulting in at least $15 million in gross
proceeds to the Company and reflecting a corporation valuation of at least $50
million. In addition, GSCP and the Kleiner Entities have delivered irrevocable
proxies to Intuit to vote their Series B Preferred shares for an Intuit
director designee in the event that Intuit fully exercises its warrants to
purchase Series B shares. The latter proxies terminate upon the earliest of
(a) Intuit's ceasing to hold at least half of its Series B shares, (b) the
conversion of all Series B Preferred Stock into Common Stock, and (c) the
closing of a public offering resulting in at least $15 million in gross
proceeds to the Company and reflecting a corporation valuation of at least $50
million.
 
  Pursuant to a Shareholder Agreement entered into in connection with the
Company's sale of Series D Preferred Stock, each of Racal, TMI and SOFTBANK
has agreed, until the earlier of (i) the date on which the number of
outstanding Series D Preferred shares falls below certain specified minimums
and (ii) the occurrence of a qualified public offering of the Company's Common
Stock, to vote the shares of Common Stock and Preferred Stock controlled by
them to elect as Directors that number of Series D Directors provided for in
the Amended and Restated Articles of Incorporation, to be designated in
accordance with the respective holdings of the three parties. Currently, each
of Racal, TMI and SOFTBANK is entitled to designate one director, and each of
the three agrees to vote all shares of Common Stock and Preferred Stock
controlled by it to elect the designees of the other two parties.
 
  Each of the foregoing voting arrangements will terminate upon completion of
the offering.
 
  Pursuant to a Governance Agreement entered into among GSCP, the Kleiner
Entities, Intuit, Mr. Collins-Rector, Mr. Shackley and the Company (the
"Government Agreement"), Mr. Collins-Rector and Mr. Shackley are jointly
enabled to designate one member of the Company's Board of Directors. The
Governance Agreement also obligates the Company to use reasonable efforts to
maintain such designee on the Board of Directors until the earlier to occur of
(i) one year after the closing of the Company's initial public offering, (ii)
the expiration or full release of Mr. Collins-Rector and Mr. Shackley from any
lock-up restrictions granted to the underwriters in connection with such
initial public offering, or (iii) the sale of all or substantially all of the
assets of the Company or the merger, acquisition or other reorganization of
the Company in which more than 50% of the voting power of the Company is
disposed of. Initially, such designee is Robert W. Doede.
 
  Randy Maslow has submitted his resignation as a director of the Company, to
be effective as of the closing of the offering made hereby. In connection with
this resignation, the Company has agreed to invite Mr. Maslow to observe all
meetings of the Company's Board of Directors and committee meetings of the
Board for the six month period following the effective date of the offering.
The Company has agreed to place a designee of Williams Communications Group,
Inc. on the Board of Directors to fill the vacancy left by Mr. Maslow's
resignation.
 
 Director Compensation
 
  Directors are reimbursed for certain reasonable expenses incurred in
attending Board or committee meetings. Officers of the Company are elected
annually by the Board of Directors and serve at its discretion. The Company
has entered into indemnification agreements with each member of the Board of
Directors and certain of its officers providing for the indemnification of
such person to the fullest extent authorized, permitted or allowed by law.
 
                                      52
<PAGE>
 
 Compensation Committee
 
  The Company's Board of Directors currently has a Compensation Committee that
reviews and approves the compensation and benefits to be provided to the
officers, directors, employees, and consultants of the Company, administers
the Company's 1993 Incentive Stock Option Plan, 1995 Stock Incentive Plan for
Employees and Consultants, and Amended and Restated 1996 Stock Plan, and will
administer the 1997 Stock Plan and 1997 Employee Stock Purchase Plan, which
are to take effect upon closing of the Company's initial public offering. The
Compensation Committee currently consists of Messrs. Khosla and Rieschel.
 
 Audit Committee
 
  The Company's Board of Directors currently has an Audit Committee that
monitors the corporate financial reporting and the internal and external
audits of the Company, reviews and approves material accounting policy
changes, monitors internal accounting controls, to recommend engagement of
independent auditors, reviews related-party transactions and performs other
duties as prescribed by the Board of Directors. The Audit Committee currently
consists of Messrs. Bender, Regis and Doede.
 
EXECUTIVE COMPENSATION
 
  Summary Compensation. The following table sets forth in summary form the
compensation earned by the Company's Chief Executive Officer, and the four
most highly compensated executive officers (the "Named Officers") during 1996.
 
<TABLE>
<CAPTION>
                                                                      LONG-TERM
                                      ANNUAL COMPENSATION            COMPENSATION
                             --------------------------------------- ------------
                                                                      SECURITIES   ALL OTHER
                                                      OTHER ANNUAL    UNDERLYING  COMPENSATION
NAME AND PRINCIPAL POSITION  SALARY ($) BONUS ($)   COMPENSATION ($) OPTIONS (#)     ($)(3)
- ---------------------------  ---------- ---------   ---------------- ------------ ------------
<S>                          <C>        <C>         <C>              <C>          <C>
Henry R. Nothhaft.......      184,808       --              --             --        3,105
 President and Chief
 Executive Officer
John K. Peters..........      184,273       --              --             --        3,076
 Executive Vice
 President and General
 Manager, Network
 Services Division
Michael F. Anthofer.....      136,336    20,000         155,212(2)      43,333(4)    1,545
 Senior Vice President
 and Chief Financial
 Officer
George D. Carr..........      105,000    25,897(1)          --           6,666(4)    1,761
 Vice President of Field
 Sales
Scott G. Eagle..........      114,337       --           82,396(2)      30,000(4)    1,347
 Vice President of
 Marketing
</TABLE>
- --------
(1) Reflects sales commissions.
(2) Reflects relocation expense payments.
(3) Reflects Company contributions to an employee 401(k) plan and term life
    insurance premiums paid by the Company.
(4) Includes certain options that were granted at higher fair market values
    earlier in 1996 and repriced by amendment in April 1996 to reflect lower
    fair market values at that time.
 
                                      53
<PAGE>
 
  Option Grants During 1996. The following table sets forth for each of the
Named Officers certain information concerning stock options granted during
1996.
<TABLE>
<CAPTION>
                                                                                                      
                                                                                                      
                                                                                                      
                                                                                                      
                                                                                                      
                                                                                          POTENTIAL     
                                                                                          REALIZABLE    
                                                                                           VALUE AT     
                                            INDIVIDUAL GRANTS(3)                        ASSUMED ANNUAL  
                         ------------------------------------------------------------   RATES OF STOCK  
                                       PERCENT OF               MARKET                      PRICE       
                           NUMBER OF     TOTAL                 PRICE OF                  APPRECIATION   
                          SECURITIES    OPTIONS               SECURITIES                 FOR OPTIONS    
                          UNDERLYING   GRANTED TO EXERCISE    UNDERLYING                   TERM(2)      
                            OPTIONS    EMPLOYEES    PRICE     OPTIONS ON   EXPIRATION   --------------  
   NAME                  GRANTED(1)(3)  IN 1996   PER SHARE  DATE OF GRANT    DATE      5%($)  10%($)   
   ----                  ------------- ---------- ---------  ------------- ----------   ------ -------  
<S>                      <C>           <C>        <C>        <C>           <C>          <C>    <C>      
Henry R. Nothhaft.......       --         --          --           --             --       --      --   
John K. Peters..........       --         --          --           --             --       --      --   
Michael F. Anthofer.....    33,333        7.9%      $3.75(4)     $3.75     12/31/2004   59,681 142,947  
                            10,000        2.4       $3.75        $4.80     12/31/2006   40,687  87,000  
George D. Carr..........     3,333        0.8       $3.75(4)     $3.75      2/28/2005    6,891  16,973  
                             3,333        0.8       $3.75        $4.80     12/31/2006   13,561  28,997  
Scott G. Eagle..........    30,000        7.1       $3.75(4)     $3.75      3/31/2005   62,024 152,769   
</TABLE>
 
- --------
(1) Options vest with respect to 25% of the shares on the first anniversary
    date of grant and the remaining 75% vests monthly over the succeeding
    three years.
(2) Potential Realizable Value is based on the assumption that the Common
    Stock of the Company appreciates at the annual rate shown (compounded
    annually) from the date of grant until the expiration of the option term.
    These numbers are calculated based on the requirements promulgated by the
    Securities and Exchange Commission and do not reflect the Company's
    estimate of future stock price growth.
(3) Excludes 74,666, 63,466, 43,333, 16,666 and 3,333 shares subject to
    options granted to Messrs. Nothhaft, Peters, Anthofer, Carr and Eagle,
    respectively, subsequent to 1996.
(4) These options were granted at an exercise price determined by the Board of
    Directors to be equal to the fair market value of the Company's shares on
    the date of grant. The Company's Common Stock was not traded publicly at
    the time of the option grants to the Named Officers. The options were
    granted at higher fair market values earlier in 1996 and repriced by
    amendment in April to reflect fair market values at that time.
 
  Aggregate Option Exercises in 1996 and Year-End Option Values. The following
table sets forth for each of the Named Officers certain information concerning
the number of shares subject to both exercisable and unexercisable stock
options as of December 31, 1996. Also reported are values for "in-the-money"
options that represent the positive spread between the respective exercise
prices of outstanding options and the fair market value of the Company's
Common Stock as of December 31, 1996. No Named Officer exercised options
during 1996.
 
<TABLE>
<CAPTION>
                               NUMBER OF SECURITIES      VALUE OF UNEXERCISED
                              UNDERLYING UNEXERCISED    IN-THE-MONEY OPTIONS AT
                              OPTIONS AT 12/31/96(#)        12/31/96($)(1)
                             ------------------------- -------------------------
   NAME                      EXERCISABLE UNEXERCISABLE EXERCISABLE UNEXERCISABLE
   ----                      ----------- ------------- ----------- -------------
<S>                          <C>         <C>           <C>         <C>
Henry R. Nothhaft...........   73,210       76,124       76,871       79,930
John K. Peters..............   59,832       67,101       62,824       70,456
Michael F. Anthofer.........     --         43,333          --        45,500
George D. Carr..............    2,917       13,750        3,063       14,438
Scott G. Eagle..............     --         30,000          --        31,500
</TABLE>
- --------
(1) Calculated by determining the difference between the fair market value of
    the securities underlying the option at December 31, 1996 ($4.80 per
    share) and the exercise price of the Named Officer's option.
 
EMPLOYEE STOCK PLANS
 
  1995 Stock Incentive Plan for Employees and Consultants. The Company's 1995
Stock Incentive Plan for Employees and Consultants (the "1995 Plan") provides
for the granting to employees of incentive stock options within the meaning of
Section 422 of the Internal Revenue Code of 1986, as amended (the "Code"), and
for the granting to
 
                                      54
<PAGE>
 
employees and consultants of nonstatutory stock options, stock appreciation
rights ("SARs") and restricted stock awards ("RSAs"). No SARs or RSAs have
been granted under the 1995 Plan. The 1995 Plan was approved by the Board of
Directors in September 1995 and Stockholders in September 1995, and an
amendment decreasing the number of shares thereunder from 840,000 to 762,600
was approved by the Board of Directors in February 1996. The 1995 Plan was
terminated effective October 4, 1996, and no further grants are being made
thereunder except to the extent that an exchange of options under the
Company's 1993 Incentive Stock Option Plan for options under the 1995 Plan,
which exchange was begun in October 1995, is continuing and has not yet been
completed. A total of 762,600 shares of Common Stock are reserved for issuance
pursuant to the 1995 Plan. As of June 30, 1997, options to purchase 346,500
shares of Common Stock at a weighted exercise price of $3.75 per share were
outstanding under the 1995 plan.
 
  The 1995 Plan is administered by a committee of the Board of Directors,
which committee is required, once the Company's Common Stock becomes publicly
traded, to be constituted to comply with Rule 16b-3 promulgated under the
Securities Exchange Act of 1934, as amended, and applicable laws. The
administrator has the power to determine the terms of the options granted,
including the exercise price, the number of shares subject to the option and
the exercisability thereof, and the form of consideration payable upon
exercise. Options granted under the 1995 Plan are not generally transferable
by the optionee, and each option is exercisable during the lifetime of the
optionee only by such optionee. Incentive stock options granted under the 1995
Plan must generally be exercised within three months of the end of an
optionee's status as an employee or consultant of the Company, or within 12
months after such optionee's termination by death or disability, but in no
event later than the expiration of the option's term, which may not exceed ten
years. The exercise price of all options granted under the 1995 Plan must be
at least equal to the fair market value of the Common Stock on the date of
grant. With respect to any participant who owns stock possessing more than 10%
of the voting power of all classes of the Company's outstanding capital stock,
the exercise price of any option must equal at least 110% of the fair market
value on the grant date and the term of the option must not exceed five years.
The term of all other options granted under the 1995 Plan may not exceed 10
years.
 
  The 1995 Plan provides that in the event of a recapitalization, stock split,
stock dividend, combination or reclassification or other increase or decrease
in the number of issued shares of Common Stock without consideration, the
number of shares subject to each outstanding stock option, as well as the
exercise price are appropriately adjusted as determined by the Committee.
 
  Amended and Restated 1996 Stock Plan. The Company's Amended and Restated
1996 Stock Plan (the "Restated 1996 Plan") provides for the granting to
employees of incentive stock options within the meaning of Section 422 of the
Code, and for the granting to employees, directors and consultants of
nonstatutory stock options and stock purchase rights ("Rights"). The 1996 Plan
was initially approved by the Board of Directors effective as of December
1996. It was amended and restated in May 1997 and approved by the Stockholders
at the 1997 annual meeting. Unless terminated sooner, the Restated 1996 Plan
will terminate automatically in December 2006. A total of 1,100,000 shares of
Common Stock are currently reserved for issuance pursuant to the Restated 1996
Plan. As of June 30, 1997, options to purchase 844,513 shares of Common Stock
at a weighted average exercise price of $6.45 per share were outstanding, and
255,487 shares of Common Stock remained available for future grant under the
Restated 1996 Stock Plan.
 
  The Restated 1996 Plan may be administered by a committee of the Board of
Directors constituted to comply with applicable laws (the "Committee") or by
the Board itself. The Board or Committee (the "Administrator") has the power
to determine the terms of the options or Rights granted, including the
exercise price, the number of shares subject to each option or Right, the
exercisability thereof, or any vesting acceleration or waiver of forfeiture
conditions. The Administrator may determine the form of payment upon exercise,
including cash, check, promissory note, other shares, cashless exercise or a
combination of the foregoing. The Board has the authority to amend, suspend or
terminate the Restated 1996 Plan, provided that no such action may impair the
rights of any optionee or Right holder without that person's consent.
 
  Options and Rights granted under the Restated 1996 Plan are not generally
transferable by the optionee or Right holder other than by will or the laws of
descent and distribution, and each option and Right is exercisable
 
                                      55
<PAGE>
 
during the lifetime of the optionee or Right holder only by such optionee or
Right holder. The form of option agreement currently in use provides that
options generally must be exercised within 90 days of the end of optionee's
status as an employee, director or consultant of the Company. Under the Plan,
options must be exercised within twelve months after such optionee's
termination by death or disability, but in no event later than the expiration
of the option's term. In the case of Rights, unless the Administrator
determines otherwise, the Restricted Stock Purchase Agreement shall grant the
Company a repurchase option exercisable upon the voluntary or involuntary
termination of the purchaser's service with the Company for any reason
(including death or disability). The purchase price for shares repurchased
pursuant to the Restricted Stock Purchase Agreement shall be the original
price paid by the purchaser and may be paid by cancellation of any
indebtedness of the purchaser to the Company. The repurchase option shall
lapse at a rate determined by the Administrator but in no case more slowly
than 20% per year over five years. Generally, options vest 25% after one year
and 1/36 per month thereafter. The exercise price of all incentive stock
options granted under the Restated 1996 Plan must be at least equal to the
fair market value of the Common Stock on the date of grant. The exercise price
of nonstatutory stock options and Rights must at least be equal to 85% of the
fair market value of the Common Stock on the date of grant. With respect to
any participant who owns stock possessing more than 10% of the voting power of
all classes of the Company's outstanding capital stock, the exercise price of
any incentive or nonstatutory stock option granted must equal at least 110% of
the fair market value on the grant date. The term of an incentive stock option
granted to such a 10% Stockholder must not exceed five years. The term of
other options granted under the Restated 1996 Plan may not exceed ten years.
 
  The Restated 1996 Plan provides that in the event of a merger of the Company
with or into another corporation, a sale of substantially all of the Company's
assets or a like transaction involving the Company, each option shall be
assumed or an equivalent option substituted by the successor corporation. If
the outstanding options are not assumed or substituted as described in the
preceding sentence, the Administrator shall provide for the optionee or Right
holder to have the right to exercise the option or Right as to all of the
optioned stock, including shares as to which it would not otherwise be
exercisable. If the Administrator makes an option or Right exercisable in full
in the event of a merger or sale of assets, the Administrator shall notify the
optionee or Right holder that the option or Right shall be fully exercisable
for a period of fifteen days from the date of such notice, and the option or
Right will terminate upon the expiration of such period. The forms of option
agreement and restricted stock purchase agreement currently in use provide for
a 180-day lockup of the optionee's or Right holder's shares in the event of
the Company's initial public offering. The option exercise notice and the
restricted stock purchase agreement also grant the Company a right of first
refusal (prior to the initial public offering) on the sale or transfer of any
shares purchased pursuant to an option or Right, other than transfers by gift,
operation of law or certain family transfers.
 
  1997 Stock Plan. The Company's 1997 Stock Plan (the "1997 Plan") provides
for the granting to employees of incentive stock options within the meaning of
Section 422 of the Internal Revenue Code of 1986, as amended (the "Internal
Revenue Code"), and for the granting to employees, directors and consultants
of nonstatutory stock options and stock purchase rights ("Rights"). The 1997
Plan will be presented to the Board of Directors and to the stockholders in
June 1997. Unless terminated sooner, the 1997 Plan will terminate
automatically in 2007. A total of 1,500,000 shares of Common Stock are
currently reserved for issuance pursuant to the 1997 Plan.
 
  The 1997 Plan may be administered by a committee of the Board of Directors
(the "Committee") or by the Board itself. In the case of options intended to
qualify as "performance-based compensation" within the meaning of Section
162(m) of the Code, the Committee shall consist of two or more "outside
directors" within the meaning of Section 162(m) of the Code. The Board or
Committee (the "Administrator") has the power to determine the terms of the
options or Rights granted, including the exercise price, the number of shares
subject to each option or Right, the exercisability thereof, and the form of
consideration payable upon such exercise. In addition, the Administrator has
the authority to amend, suspend or terminate the 1997 Plan, provided that no
such action may impair the rights of any optionee or Right holder without such
person's consent under the 1997 Plan.
 
  Except in connection with his or her initial engagement with the Company, no
employee, director or consultant may be granted options or Rights for more
than 500,000 shares in any one fiscal year. Options and Rights granted under
the 1997 Plan are not generally transferable by the optionee or Right holder,
and each option and Right is exercisable during the lifetime of the optionee
or Right holder only by such optionee or Right holder. Options granted
 
                                      56
<PAGE>
 
under the 1997 Plan must generally be exercised within three months of the end
of optionee's status as an employee, director or consultant of the Company, or
within twelve months after such optionee's termination by death or disability,
but in no event later than the expiration of the option's term. In the case of
Rights, unless the Administrator determines otherwise, the restricted stock
purchase agreement shall grant the Company a repurchase option exercisable
upon the voluntary or involuntary termination of the purchaser's employment
with the Company for any reason (including death or disability). The purchase
price for shares repurchased pursuant to the restricted stock purchase
agreement shall be the original price paid by the purchaser and may be paid by
cancellation of any indebtedness of the purchaser to the Company. The
repurchase option shall lapse at a rate determined by the Administrator. The
exercise price of all incentive stock options granted under the 1997 Plan must
be at least equal to the fair market value of the Common Stock on the date of
grant. The exercise price of nonstatutory stock options and Rights granted
under the 1997 Plan is determined by the Administrator, but with respect to
nonstatutory stock options intended to qualify as "performance-based
compensation" within the meaning of Section 162(m) of the Code, the exercise
price must at least be equal to the fair market value of the Common Stock on
the date of grant. With respect to any participant who owns stock possessing
more than 10% of the voting power of all classes of the Company's outstanding
capital stock, the exercise price of any incentive stock option granted must
equal at least 110% of the fair market value on the grant date and the term of
such incentive stock option must not exceed five years. The term of other
incentive stock options granted under the 1997 Plan may not exceed ten years.
 
  The 1997 Plan provides that in the event of a merger of the Company with or
into another corporation, a sale of substantially all of the Company's assets
or a like transaction involving the Company, each option shall be assumed or
an equivalent option substituted by the successor corporation. If the
outstanding options are not assumed or substituted as described in the
preceding sentence, the Administrator shall provide for the optionee or Right
holder to have the right to exercise the option or Right as to all of the
optioned stock, including shares as to which it would not otherwise be
exercisable. If the Administrator makes an option or Right exercisable in full
in the event of a merger or sale of assets, the Administrator shall notify the
optionee or Right holder that the option or Right shall be fully exercisable
for a period of fifteen days from the date of such notice, and the option or
Right will terminate upon the expiration of such period.
 
  1997 Employee Stock Purchase Plan. The Company's 1997 Employee Stock
Purchase Plan (the "1997 Purchase Plan") will be presented to the Board of
Directors and to the stockholders in June 1997. A total of 500,000 shares of
Common Stock has been reserved for issuance under the 1997 Purchase Plan. The
1997 Purchase Plan, which is intended to qualify under Section 423 of the
Internal Revenue Code, consists of 24-month offering periods beginning on the
first trading day on or after February 15 and August 15 of each year, except
for the first such offering period, which commences on the first trading day
on or after the Company's initial public offering effective date of the and
ends on the last trading day. Each offering period contains four six-month
purchase periods. The 1997 Purchase Plan is administered by the Board of
Directors or by a committee appointed by the Board. Employees are eligible to
participate if they are customarily employed by the Company or any designated
subsidiary for at least 20 hours per week and more than five months in any
calendar year. The 1997 Purchase Plan permits eligible employees to purchase
Common Stock through payroll deductions of up to 10% of an employee's
compensation (excluding overtime, shift premium, and other bonuses and
incentive compensation), up to a maximum of $25,000 for all offering periods
ending within the same calendar year. No employee may purchase more than
25,000 shares in any purchase period. The price of stock purchased under the
1997 Purchase Plan is 85% of the lower of the fair market value of the Common
Stock at the beginning of the offering period or at the end of the current
purchase period. Employees may end their participation at any time during an
offering period, and they will be paid their payroll deductions to date.
Participation ends automatically upon termination of employment with the
Company.
 
  Rights granted under the 1997 Purchase Plan are not transferable by a
participant other than by will, the laws of descent and distribution, or as
otherwise provided under the 1997 Purchase Plan. The 1997 Purchase Plan
provides that, in the event of a merger of the Company with or into another
corporation or a sale of substantially all of the Company's assets, each
outstanding option shall be assumed or an equivalent option shall be
substituted for it, or the Board of Directors or its committee shall shorten
the purchase and offering periods then in progress (so that employees' rights
to purchase stock under the Plan are exercised prior to the merger or sale of
assets). The 1997
 
                                      57
<PAGE>
 
Purchase Plan will terminate in 2007. The Board of Directors has the authority
to amend or terminate the 1997 Purchase Plan, except that no such action may
adversely affect any outstanding rights to purchase stock under the 1997
Purchase Plan.
 
COMPENSATION COMMITTEE INTERLOCKS AND INSIDER PARTICIPATION
 
  None of the current members of the Compensation Committee is an executive
officer of the Company.
 
                                       58
<PAGE>
 
                             CERTAIN TRANSACTIONS
 
PREFERRED STOCK ISSUANCES
 
  The Company has sold shares of its Preferred Stock in private financings
from April 1995 through June 1997 as follows (all share amounts set forth in
this "Certain Transactions" section reflect the one-for-15 reverse stock split
of the Company's Common Stock and Preferred Stock that will occur prior to the
closing of the offering but do not reflect the conversion of outstanding
shares of Preferred Stock into shares of Common Stock that will occur
automatically immediately prior to the closing of the offering): 906,454
shares of Series A Preferred Stock at an effective price of $11.00 per share;
433,634 shares of Series B Preferred Stock at an effective price of $11.00 per
share; 928,243 shares of Series C Preferred Stock at an effective price of
$27.30 per share; and 2,933,248 shares of Series D Preferred Stock at an
effective price of $20.40 per share.
 
<TABLE>
<CAPTION>
  DIRECTORS, EXECUTIVE    SHARES OF SHARES OF SHARES OF                  SHARES OF
      OFFICERS AND         COMMON   SERIES A  SERIES B  SHARES OF SERIES SERIES D
    5% STOCKHOLDERS         STOCK   PREFERRED PREFERRED   C PREFERRED    PREFERRED WARRANTS
  --------------------    --------- --------- --------- ---------------- --------- --------
<S>                       <C>       <C>       <C>       <C>              <C>       <C>
The Goldman Sachs Group,
 L.P.(1)................   167,246   453,227   216,817      123,297         14,706  57,595
Kleiner Perkins Caufield
 & Byers entities(2)....   167,246   453,227   216,817          --          14,706 148,504
TMI Telemedia
 International,
 Ltd.(3)................       --        --        --           --       1,184,642 325,786
SOFTBANK Holdings
 Inc.(4)................       --        --        --           --         980,393     --
Racal Data Group(5).....       --        --        --           --         490,197 491,631
Henry R. Nothhaft(6)....       --        --        --           --             --    4,902
John Peters(7)..........       --        --        --           --             --    2,451
</TABLE>
- --------
(1) Consists of securities held of record by GS Capital Partners, L.P. See
    "Principal Stockholders." Includes 90,938 shares of Common Stock issued
    upon exercise of warrants in April 1997 at an exercise price of $6.60 per
    share, 33,344 shares of Series B Preferred Stock issued upon exercise of
    warrants in April 1997 at an exercise price of $6.60 per share, and 14,706
    shares of Series D Preferred Stock issued upon exercise of warrants in
    April 1997 at an exercise price of $12.24 per share. GS Capital Partners
    L.P. exercised such warrants at a discounted exercise price in
    consideration of its early exercise. Terence M. O'Toole, a Director of the
    Company, is a Managing Director of Goldman, Sachs & Co., the investment
    manager for GS Capital Partners, L.P. See "Principal Stockholders."
(2) Vinod Khosla, a director of the Company, is a general partner of KPCB VII
    Associates, the general partner of Kleiner Perkins Caufield & Byers VII
    and KPCB VII Information Sciences Zaibatsu Fund II. Includes 90,938 shares
    of Common Stock issued upon exercise of warrants in April 1997 at an
    exercise price of $6.60 per share 33,344 shares of Series B Preferred
    Stock issued upon exercise of warrants in April 1997 at an exercise price
    of $6.60 per share, and 14,706 shares of Series D Preferred Stock issued
    upon exercise of warrants in April 1997 at an exercise price of $12.24 per
    share. The Kleiner Entities exercised such warrants at a discounted
    exercise price in consideration of their early exercise.
(3) Franco Regis, a director of the Company, is Director of Business
    Development and Strategic Planning of Telecom Italia, SpA, the parent of
    TMI Telemedia International, Ltd. Includes 204,248 shares of Series D
    Preferred issued upon exercise of a warrant in April 1997 at an exercise
    price of $12.24 per share. TMI exercised such warrants at a discounted
    exercise price in consideration of its early exercise.
(4) Gary Rieschel, a director of the Company, is Senior Vice President of
    SOFTBANK Holdings Inc. As of October 31, 1996, the shares were transferred
    by SOFTBANK Holdings Inc. to its affiliate SOFTBANK Ventures, Inc.
(5) Louis P. Bender III, a director of the Company, is the President, Americas
    Region of Racal Data Group of Racal.
(6) Henry R. Nothhaft is the President of the Company. Represents 4,902 shares
    of Series D Preferred Stock issuable upon exercise of a warrant at an
    exercise price of $20.40 per share. The warrant was granted to Mr.
    Nothhaft in July 1996 in consideration of a bridge loan in the amount of
    $100,000. The principal and interest on such bridge loan was repaid in
    full.
(7) John Peters is the Executive Vice President and General Manager Network
    Operations of the Company. Represents 2,451 shares of Series D Preferred
    Stock issuable upon exercise of a warrant at an exercise price of $20.40
    per share. The warrant was granted to Mr. Peters in July 1996 in
    consideration of a bridge loan in the amount of $50,000. The principal and
    interest on such bridge loan was repaid in full.
 
                                      59
<PAGE>
 
  The Preferred Stock described above will convert into Common Stock upon the
closing of this Offering. Holders of the Preferred Stock are entitled to
certain registration rights with respect to the Common Stock issued or
issuable upon conversion thereof. In addition, GSCP, the Kleiner Entities and
Marc Collins-Rector are entitled to certain registration rights with respect
to shares of Common Stock held by them, and employees of Critical
Technologies, Inc. have certain piggyback registration rights with respect to
shares issuable upon exercise of certain options issued to them. See
"Description of Capital Stock--Registration Rights."
 
SERIES A AGREEMENT
 
  The Preferred Stock and Warrant Purchase Agreement, dated April 20, 1995, as
amended (the "Series A Agreement") by which the Registrant sold Series A
Preferred Stock and warrants to purchase Common Stock to GSCP, Kleiner Perkins
Caufield & Byers VII and KPCB VII Founders Fund for an aggregate consideration
of approximately $10.0 million, provides that as long as GSCP and its
affiliates beneficially own five percent or more of the outstanding Common
Stock of the Registrant, Goldman, Sachs & Co. or any of its affiliates have
the right to perform all investment banking services for the Registrant on
customary terms consistent with an arms'-length transaction. The Series A
Agreement, further obligates the Registrant to complete by June 30, 1997, a
rescission offer with respect to all Common Stock and Common Stock equivalents
issued prior to April 20, 1995, and to indemnify the GSCP and the Kleiner
Entities against "rescission losses," in excess of the estimated amount of
rescission losses described in the Series A Agreement.
 
BRIDGE LOANS
 
  In connection with the alliance between Intuit and the Company, GSCP and the
Kleiner Entities made bridge loans totaling $2 million to the Company on
October 16, 1995, which were rolled over into bridge loans totaling $4 million
on November 6, 1995. On November 29, 1995, GSCP made a further bridge loan of
$3 million. In consideration of these loans, GSCP and the Kleiner Entities
received warrants to purchase 181,876 shares of Series B Preferred Stock at an
exercise price of $11.00 per share. Effective as of December 20, 1995, GSCP
and the Kleiner Entities converted the principal and interest due under their
$2 million promissory notes into a total of 366,947 shares of Series B
Preferred Stock at a price of $11.00 per share. In addition, effective as of
February 1996, GSCP converted the entire amount of principal and interest on
its $3 million bridge note into 123,297 Series C Shares at an exercise price
of $24.57 per share.
 
  On July 31, 1996, the Company closed bridge loans from GSCP and KPCB for
$300,000 each, evidenced by convertible promissory notes dated July 29, 1996.
The Company issued GSCP and KPCB each a warrant dated July 31, 1996, to
purchase 14,706 shares of Series D Preferred Stock at an exercise price of
$20.40 per share. The loans were repaid on August 21, 1996. On April 4, 1997,
the Company and GSCP and KPCB entered warrant amendment agreements reducing
the exercise price of the warrants to $12.24 per share, and the warrants were
exercised.
 
  On July 31, 1996, the Company closed bridge loans from Henry Nothhaft, the
Company's President, Chief Executive Officer and a director, and John Peters,
the Company's Executive Vice President and President, Network Services
Division, for $100,000 and $50,000, respectively. The loans were evidenced by
promissory notes dated July 29, 1996. The Company issued Mr. Nothhaft and Mr.
Peters warrants dated July 31, 1996, to purchase 4,902 shares and 2,451
shares, respectively, of Series D Preferred Stock at an exercise price of
$20.40 per share. The loans were repaid on August 21, 1996.
 
  On June 27, 1997, the Company closed a bridge loan with Kleiner Perkins
Caufield & Byers VII and KPCB Information Sciences Zaibatsu Fund VII for
$1,950,000 and $50,000, respectively, evidenced by promissory notes dated June
27, 1997. The Company issued each of the noteholders a warrant exercisable for
that number of shares of Common Stock equal to 50% of the principal amount of
the respective note divided by the Price to Public. The exercise price per
share for each of the warrants is 50% of the Price to Public. The proceeds
from the bridge loan will be used to finance a down-payment payable to
Netscape under agreements entered into between the Company and Netscape on
June 23, 1997. See "Business--Services."
 
                                      60
<PAGE>
 
COMMISSIONS
 
  The Company paid commissions totaling $350,000 to Goldman, Sachs & Co. in
August 1996 in connection with the sale of shares of Series D Preferred Stock.
Terence M. O'Toole, a Director of the Company, is a Managing Director of
Goldman, Sachs & Co.
 
WARRANT EXERCISES
 
  Effective as of April 4, 1997, the Company entered into warrant amendment
agreements with TMI, GSCP, and the Kleiner Entities to reduce the exercise
price of certain of their warrants in return for the immediate exercise of
such warrants. The exercise price of warrants for 181,876 shares of Class A
Common Stock and 66,688 shares of Series B Preferred Stock held by GSCP and
the Kleiner Entities was reduced from $11.00 to $6.60 per share. The exercise
price of warrants for 233,660 shares of Series D Preferred Stock held by GSCP,
KPCB and TMI was reduced from $20.40 per share to $12.24 per share. Also, in
connection with the reduction of the exercise price of the GSCP and Kleiner
Entities' Common Stock warrants, the exercise price of Intuit's $1.5 million
warrant was similarly reduced to $6.60 per share, and the expiration date was
extended to December 31, 2000.
 
RACAL TRANSACTION
 
  Pursuant to a master lease agreement between the Company and Racal-Datacom,
Inc. ("Racal"), effective March 31, 1995, the Company has installed networking
equipment under lease financing. The terms of the leases under the master
agreement are 48 months or 60 months, depending on the equipment. In 1996, the
Company paid Racal approximately $8.3 million in lease payments and related
charges. As of December 31, 1996, the current portion of the Company's capital
lease obligations to Racal totaled $10.2 million, and the noncurrent portion
totaled $29.2 million. As security for the lease financing, Racal has a
security interest in all leased equipment.
 
AMPM TRANSACTIONS
 
  Donald C. Schutt, Vice President of Michigan Operations for the Company, is
a majority stockholder of AMPM, Inc., an advertising agency. The Company
incurred marketing fees payable to AMPM, Inc. totaling $2.5 million in 1996.
The Company believes that the fees charged by AMPM for such services are
competitive with those of similar advertising agencies.
 
EMPLOYMENT AND TERMINATION AGREEMENTS
 
  In February 1996, the Company entered into a termination of services and
indemnification agreement with Marc Collins-Rector and Chad Shackley (the
"Founders"). Pursuant to such agreement Mr. Collins-Rector agreed to resign
from the Board of Directors of the Company and the Founders agreed to resign
as Company employees and to enter into lock-up agreements in the event of the
Company's initial public offering. If asked to do so by the Founders, the
Company agreed it will file a registration statement on Form S-8 or Form S-3
by certain deadlines after it becomes eligible to do so, with respect to
certain shares issuable upon exercise of the Founders' options.
 
  Also in February 1996, the Company entered into an agreement with Randy
Maslow wherein Mr. Maslow agreed to serve as an advisor to the Board of
Directors through October 31, 1996. Mr. Maslow has since resigned from the
Board effective upon the effectiveness of an initial public offering. Mr.
Maslow will be invited to all meetings of the Company's Board of Directors and
committee meetings of the Board for six months after the effective date of the
offering made hereby. If asked to do so by Mr. Maslow, the Company agreed it
will file a registration statement on Form S-8 or Form S-3 as soon as
practicable after it becomes eligible to do so, with respect to certain shares
issuable upon exercise of Mr. Maslow's options.
 
OPTIONS OF MANAGEMENT AND DIRECTORS
   
  In July 1996, the Company amended the terms of options to purchase 53,341
shares of Common Stock previously issued to Donald C. Schutt, an executive
officer of the Company to decrease the exercise price to $3.75 per share and
remove certain conditions precedent to vesting of such options.     
 
                                      61
<PAGE>
 
  In August 1996, the Board of Directors amended the vesting provisions of
options to purchase 14,000 shares issued to Henry Nothhaft, President, Chief
Executive Officer and a director of the Company, on October 31, 1995, and an
option to purchase 11,900 shares issued to John Peters, Executive Vice
President and General Manager, Network Services Division, on October 31, 1995,
so the options would fully vest as of the closing date of the sale of at least
$29 million of Series D Preferred Stock of the Company, which occurred on
August 21, 1996.
 
  In August 1996, the Company exchanged four options previously issued to Randy
Maslow, a director of the Company, for new options exercisable for an aggregate
of 46,673 shares of Class A Common Stock at $3.75 per share. The four-year
vesting schedule accelerates so that all shares vest immediately in the event
of an initial public offering or a change of control. The options may be
exercised through their expiration date regardless of when Mr. Maslow ceases
being an employee or consultant. Mr. Maslow's employment with the Company ended
on October 31, 1996.
       
  In May 1997, the Company amended options to purchase 26,666 shares of Common
Stock previously issued to Marc Collins-Rector, a founder and 5% shareholder of
the Company's Common Stock, to remove vesting conditions.
 
WILLIAMS TRANSACTION
 
  On May 30, 1997, the Company signed a non-binding Memorandum of Understanding
("MOU") with Williams Communications Group, Inc. ("WCG"), the parent company of
Critical Technologies, Inc. ("CTI"). The MOU sets forth the terms of a two-
phase investment in the Company by WCG consisting of (i) a bridge loan made by
WCG to the Company as part of phase one, (ii) WCG's participation in the Direct
Placements which are to close concurrently with this offering as part of phase
two and (iii) an expanded strategic business relationship between the parties
to be implemented in both phases. The first phase, which closed on June 19,
1997, consisted of a $3 million loan to the Company by WCG evidenced by a 10%
convertible secured promissory note (the "WCG Note") and the issuance to WCG of
a warrant to purchase shares of the Company's Common Stock. The WCG Note will
automatically convert into shares of the Company's Common Stock upon the
closing of the offering made hereby at a per share conversion price equal to
the Price to Public in the offering made hereby. The warrant is exercisable for
that number of shares of Common Stock equal to 25% of the shares issuable upon
conversion of the WCG Note at a per share exercise price of 50% of the Price to
Public. In addition to the WCG Note and the warrant, as part of the first phase
of the investment the parties amended and restated the Employee Services and
Staffing Agreement between CTI and the Company (the "CTI Agreement") and
amended the Co-location Services Agreement between CTI and the Company to,
among other things, extend the respective terms of such agreements until
December 31, 2000 and forego a $1.1 million acquisition fee to be paid by CTI
to the Company as a result of the acquisition of CTI by WCG. In exchange for
the waiver of the acquisition fee, WCG has agreed to issue $1.1 million in
telecommunications service credits to the Company. The service credits granted
to the Company will be applied to each monthly invoice from WCG for
telecommunications services provided to the Company at a rate of 50% of the
face value of services rendered until the credits have been consumed or until
five years from the closing of this offering. The parties also executed a term
sheet reflecting the basic terms of a distribution agreement and an agency
agreement to be executed as part of the first phase of the investment by which
WCG may sell CTI products and services for an initial term of two years.
 
  The MOU contemplates that the second phase of the WCG investment will take
place concurrently with the closing of this offering and will consist of the
purchase by WCG of at least $12 million of unregistered shares of the Company's
Common Stock as part of the Direct Placements. The Company will also issue
warrants to WCG to purchase that number of shares of the Company's Common Stock
equal to 25% of the shares issuable in connection with the phase two
investment, assuming for purposes of determining the size of the warrant, the
issuance of shares in exchange for an additional $2 million in services and
equipment to be provided by WCG. The exercise price of the phase two warrants
will be 50% of the Price to Public in the offering made hereby. The MOU also
provides that in the event the Company is acquired by certain competitors of
WCG, WCG shall have the right to purchase a nonexclusive, perpetual license to
use, distribute and modify all of the intellectual property of the Company,
including any copyright, patent, license, trademark or trade secret which the
Company has or obtains the right to transfer. Under the MOU, so long as WCG
owns at least 5% of the outstanding Common Stock of the Company, WCG will be
entitled to name a nominee of its choice to a seat on the Board of Directors to
be recommended to the stockholders of the Company. The Company has agreed to
place the WCG designee on the Board of Directors to fill the vacancy to
 
                                       62
<PAGE>
 
   
be left by the resignation of Randy Maslow which is to be effective upon the
effectiveness of the offering. Finally, upon completion of this offering, the
MOU provides that WCG and the Company will enter into an agreement whereby the
Company will agree to purchase a total of at least $21.2 million in
telecommunications equipment and services from WCG during the five year period
following the offering. Of the $21.1 million in equipment and services to be
purchased by the Company, up to $2.0 million may be paid, at the election of
WCG, by the issuance of common stock by the Company at the then-current fair
market value.     
 
  All future transactions among the Company and its officers, directors,
principal stockholders and their affiliates will be approved by a majority of
the Board of Directors, including a majority of the independent and
disinterested directors.
 
                                       63
<PAGE>
 
                            PRINCIPAL STOCKHOLDERS
   
  The following table sets forth certain information with respect to the
beneficial ownership of the Common Stock as of June 30, 1997, and assuming
conversion of Preferred Stock to Common Stock, and as adjusted to reflect the
sale of the 3,600,000 shares of Common Stock offered hereby and an assumed
1,636,363 shares to be sold in the Direct Placements, by: (i) each person who
is known by the Company to own beneficially more than 5% of the Common Stock;
(ii) each director and Named Officer of the Company; and (iii) all directors
and executive officers of the Company as a group. Except as otherwise noted,
the persons named in the table have sole voting and investment power with
respect to all shares of Common Stock shown as beneficially owned by them,
subject to community property laws where applicable.     
 
<TABLE>   
<CAPTION>
                                 SHARES        PERCENT BENEFICIALLY OWNED
                              BENEFICIALLY -----------------------------------
     NAMES AND ADDRESSES         OWNED     BEFORE OFFERING AFTER OFFERING(1)**
     -------------------      ------------ --------------- -------------------
<S>                           <C>          <C>             <C>
TMI Telemedia International,
 Ltd.(2).....................  1,580,968        19.6%             12.0%
 Viale del Campo Boario, 56D
 00153 Rome, Italy
The Goldman Sachs Group,
 L.P.(3).....................  1,089,645        14.0               8.5
 85 Broad Street
 New York, NY 10004
Racal-Datacom, Inc.(4).......  1,025,349        12.5               7.7
 1601 North Harrison Parkway
 Sunrise, FL 333233-2899
SOFTBANK Ventures, Inc. .....  1,026,179        13.3               8.0
 c/o SOFTBANK Holdings Inc.
 10 Langley Road, Suite 403
 Newton Center, MA 02159
Kleiner Perkins Caufield &
 Byers Entities(5)...........  1,014,453        12.9               7.8
 2750 Sand Hill Road
 Menlo Park, CA 94025
Marc Collins-Rector(6).......    649,562         8.3               5.0
 2000 Benedict Canyon
 Beverly Hills, CA 90210
Henry R. Nothhaft(7).........    100,896         1.3                 *
John K. Peters(8)............     81,569          *                  *
Michael F. Anthofer(9).......     13,889          *                  *
Scott G. Eagle(10)...........     11,667          *                  *
George D. Carr(11)...........      6,667          *                  *
Louis P. Bender III(12)......  1,025,349        12.5               7.7
Robert W. Doede..............        --          --                --
Vinod Khosla(13).............  1,014,453        12.9               7.8
Randy Maslow(14).............     46,673          *                  *
Terence M. O'Toole(15).......        --          --                --
Franco Regis(16).............  1,580,968        19.6              12.0
Gary E. Rieschel(17).........        --          --                --
All current executive
 officers and directors as a
 group (18 persons)(18)......  3,944,566        43.6%             27.9%
</TABLE>    
- --------
   * Less than 1%.
   
 ** Upon closing of the initial public offering and the Direct Placements,
    Williams Communications will beneficially own a total of 1,750,000 shares
    and exercisable warrants, or 13.3% of the Company.     
   
 (1) Applicable percentage ownership after this offering reflects the issuance
     of 3,600,000 shares in the offering and an assumed 1,636,363 shares in
     the Direct Placements and the exclusion of approximately 151,789 shares
     to be repurchased by the Company from certain stockholders who are not
     officers, directors or affiliates of the Company at the price per share
     Price to Public. Beneficial ownership is determined in accordance with
     the rules of the Securities and Exchange Commission, based on factors
     including voting and investment power with     
 
                                      64
<PAGE>
 
    respect to shares, subject to the applicable community property laws.
    Shares of Common Stock subject to options or warrants currently
    exercisable, or exercisable by August 31, 1997, are deemed outstanding for
    the purpose of computing the percentage ownership of the person holding
    such options or warrants, but are not deemed outstanding for computing the
    percentage ownership of any other person.
 (2) Includes warrants to purchase 341,001 shares of stock.
 (3) Consists of securities held of record by GS Capital Partners, L.P., an
     investment partnership, of which affiliates of The Goldman Sachs Group,
     L.P. ("GS Group") are the general partner or investment manager. GS Group
     disclaims beneficial ownership of the shares owned by GS Capital
     Partners, L.P. to the extent attributable to partnership interests
     therein held by persons other than GS Group and its affiliates. GS
     Capital Partners, L.P. shares voting and investment power with certain of
     its affiliates. Includes warrants to purchase 58,523 shares of stock.
 (4) Includes warrants to purchase 512,259 shares of stock.
   
 (5) Includes shares held by Kleiner Perkins Caufield & Byers VII, KPCB
     Information Sciences Zaibatsu Fund II and KPCB VII Founders Fund
     (collectively, the "KPCB Entities"). Also includes warrants to purchase
     149,432 shares held by the KPCB Entities.     
 (6) Includes 80,007 shares of Common Stock issuable upon exercise of
     outstanding stock options.
 (7) Includes 100,896 shares of Common Stock issuable upon exercise of
     outstanding stock options and warrants.
 (8) Includes 81,569 shares of Common Stock issuable upon exercise of
     outstanding stock options and warrants.
 (9) Includes 13,889 shares of Common Stock issuable upon exercise of
     outstanding stock options.
(10) Includes 11,667 shares of Common Stock issuable upon exercise of
     outstanding stock options.
(11) Includes 6,667 shares of Common Stock issuable upon exercise of
     outstanding stock options.
(12) Includes 1,025,349 shares and exercisable warrants held by Racal-Datacom,
     Inc. See note (4). Mr. Bender is the President of Racal-Datacom, Inc. Mr.
     Bender disclaims beneficial ownership of such shares.
   
(13) Represents shares beneficially owned by the KPCB Entities. Mr. Khosla is
     an affiliate of such entities. See note (5). Mr. Khosla disclaims
     beneficial ownership of such shares, except to the extent of his
     pecuniary interest therein.     
(14) Includes 46,673 shares of Common Stock issuable upon exercise of
     outstanding stock options.
(15) Excludes 1,089,645 shares and exercisable warrants that may be deemed to
     be beneficially owned by The Goldman Sachs Group, L.P. See note (3). Mr.
     Terence M. O'Toole, a director of the Company, serves on the Board of
     Directors as a representative of GS Capital Partners, L.P., pursuant to a
     contractual arrangement. Mr. O'Toole is a Managing Director of Goldman,
     Sachs & Co., the investment manager for GS Capital Partners, L.P. Mr.
     O'Toole disclaims beneficial ownership of such shares except to the
     extent of his pecuniary interest therein.
(16) Includes 1,580,968 shares and exercisable warrants held by TMI Telemedia
     International, Ltd. Mr. Regis is the Director of Business Development and
     Strategic Planning of Telecom Italia, S.p.A., the parent of TMI Telemedia
     International, Ltd. See note (2). Mr. Regis disclaims beneficial
     ownership of such shares.
   
(17) Excludes 1,026,179 shares held by SOFTBANK Ventures Inc. Mr. Rieschel, a
     director of the Company, is a Senior Vice President at SOFTBANK Holdings
     Inc., an affiliate of SOFTBANK Ventures Inc. Mr. Rieschel disclaims
     beneficial ownership of such shares.     
(18) Includes shares of Common Stock issuable upon exercise of outstanding
     options and warrants, and shares beneficially owned by entities
     associated with Messrs. Regis, Bender, and Khosla, as to which they
     disclaim beneficial ownership. See Notes (7)-(17).
 
                                      65
<PAGE>
 
                         DESCRIPTION OF CAPITAL STOCK
   
  Upon the completion of the offering and the Direct Placements, and the
repurchase by the Company of certain shares from certain stockholders who are
not officers, directors or affiliates of the Company at the per share Price to
Public, the outstanding Common Stock of the Company will consist of 12,804,838
shares, $0.001 par value. At July 31, 1997, there were 7,720,264 shares of
Common Stock outstanding held of record by approximately 342 stockholders.
    
  The following description of the Company's capital stock does not purport to
be complete and is subject to and qualified in its entirety by the Company's
Amended and Restated Certificate of Incorporation and Bylaws and by the
provisions of applicable Delaware law.
 
  The Amended and Restated Certificate of Incorporation and Bylaws contain
certain provisions that are intended to enhance the likelihood of continuity
and stability in the composition of the Board of Directors and which may have
the effect of delaying, deferring, or preventing a future takeover or change
in control of the Company unless such takeover or change in control is
approved by the Board of Directors.
 
COMMON STOCK
 
  A total of 100,000,000 shares of Common Stock of the Company will be
authorized upon the closing of the offering. Holders of Common Stock do not
have cumulative voting rights, and, therefore, holders of a majority of the
shares voting for the election of directors can elect all of the directors. In
such event, the holders of the remaining shares will not be able to elect any
directors.
 
  Holders of the Common Stock are entitled to receive such dividends as may be
declared from time to time by the Board of Directors out of funds legally
available therefor, subject to the terms of any existing or future agreements
between the Company and its debtholders. See "Dividend Policies." The Company
has never declared or paid cash dividends on its capital stock, expects to
retain future earnings, if any, for use in the operation and expansion of its
business, and does not anticipate paying any cash dividends in the foreseeable
future. In the event of the liquidation, dissolution or winding up of the
Company, the holders of Common Stock are entitled to share ratably in all
assets legally available for distribution after payment of all debts and other
liabilities and subject to the prior rights of any holders of Preferred Stock
then outstanding.
 
  The Common Stock has no preemptive, redemption or subscription rights. The
outstanding shares of Common Stock are, and the shares offered by the Company
will be, when issued and paid for, fully paid and nonassessable.
 
PREFERRED STOCK
 
  Effective upon the closing of the offering, the Board of Directors has the
authority, without further action by the Stockholders, to issue up to
10,000,000 shares of Preferred Stock in one or more series and to fix the
rights, preferences, privileges and restrictions thereof, including dividend
rights, conversion rights, voting rights, terms of redemption, liquidation
preferences, sinking fund terms and the number of shares constituting any
series or the designation of such series, without any further vote or action
by the Stockholders. The issuance of Preferred Stock could adversely affect
the voting power of holders of Common Stock and the likelihood that such
holders will receive dividend payments and payments upon liquidation and could
have the effect of delaying, deferring or preventing a change in control of
the Company. The Company has no present plan to issue any shares of Preferred
Stock.
 
WARRANTS
 
  As of June 30, 1997, the following warrants were outstanding (warrants noted
at items (iv) through (vii) currently are for Preferred Stock and will be
exercisable for the number of shares of Common Stock indicated below upon
conversion of Preferred Stock that will automatically occur immediately prior
to the closing of the offering):
 
    (i) Warrants to purchase 44,935 shares of Common Stock at an exercise
  price of $15.00 per share (subject to adjustment for stock splits, stock
  dividends and the like), which expire on September 1, 1998.
 
                                      66
<PAGE>
 
    (ii)   Warrants to purchase 5,000 shares of Common Stock exercisable
  through February 15, 2000, at a nominal exercise price.
 
    (iii)  Warrants to purchase 25,536 shares of Common Stock at an exercise
  price of $7.40 per share (subject to adjustment for stock splits, stock
  dividends and the like), which expire on July 20, 1998.
 
    (iv)   Warrants to purchase 117,046 shares of Common Stock at an exercise
  price of $10.82 per share (subject to adjustment for stock splits, stock
  dividends and the like), which expire on December 11, 1998.
 
    (v)    Warrants to purchase 230,938 shares of Common Stock at an exercise
  price of $6.50 per share (subject to adjustment for stock splits, stock
  dividends and the like), which expire on December 31, 2000.
 
    (vi)   Warrants to purchase 130,273 shares of Common Stock at an exercise
  price of $26.87 per share (subject to adjustment for stock splits, stock
  dividends and the like), which expire on December 31, 2000.
 
    (vii)  Warrants to purchase 38,482 shares of Common Stock at an exercise
  price of $19.49 per share (subject to adjustment for stock splits, stock
  dividends and the like), which expires on June 6, 1999. Warrants to
  purchase 35,915 shares of Common Stock at an exercise price of $19.49 per
  share (subject to adjustment for stock splits, stock dividends and the
  like), which expire on July 31, 1999. Warrant to purchase 156,072 shares of
  Common Stock at an exercise price of $19.49 per share (subject to
  adjustment for stock splits, stock dividends and the like), which expires
  on August 21, 1999. Warrants to purchase 462,324 shares of Common Stock at
  an exercise price of $19.49 per share (subject to adjustment for stock
  splits, stock dividends and the like), which expire on October 31, 1999.
  Warrant to purchase 184,930 shares of Series D Preferred Stock at an
  exercise price of $19.49 per share (subject to adjustment for stock splits,
  stock dividends and the like), which expires on March 5, 2000.
 
    (viii) Warrants to purchase shares of Common Stock equal to 25% of the
  number of shares of Common Stock issuable upon conversion of the promissory
  note issued to Williams Communications Group, Inc. Such warrants are
  exercisable after the close of this offering at an exercise price per share
  equal to 50% of the Price to Public and expires on June 19, 2002.
 
    (ix)   Warrants to purchase 90,909 shares of Common Stock at an exercise
  price per share equal to 50% of the Price to Public, which expire on June
  27, 2003.
 
REGISTRATION RIGHTS
 
  Pursuant to the agreement between the Company and holders of approximately
7,296,253 shares of Common Stock (the "Holders"), the Holders are entitled to
certain rights with respect to the registration of such shares under the
Securities Act. If the Company proposes to register any of its securities
under the Securities Act, either for its own account or for the account of
other security Holders exercising registration rights, such Holders are
entitled to notice of such registration and are entitled to include shares of
such Common Stock therein. Additionally, Holders of the Registrable Securities
are also entitled to certain demand registration rights pursuant to which they
may require the Company to file a registration statement under the Securities
Act at the Company's expense with respect to their shares of Common Stock, and
the Company is required to use its best efforts to effect such registration.
All of these registration rights are subject to certain conditions and
limitations, among them the right of the underwriters of an offering to limit
the number of shares included in such registration and the right of the
Company not to effect a requested registration within six months following an
offering of the Company's securities, including the offering made hereby.
 
  Additionally, pursuant to an agreement with Critical Technologies Inc.
("CTI"), certain employees of CTI who have been granted options to purchase an
aggregate of up to 60,000 shares of the Company's Common Stock are entitled to
certain piggyback registration rights with respect to such shares. Such rights
are subject to the right of the underwriters of an offering to limit the
number of shares included in such registration.
 
DELAWARE ANTI-TAKEOVER LAW AND CERTAIN CHARTER PROVISIONS
 
 Limitation of Director and Officer Liability
 
  The Company's Certificate of Incorporation and Bylaws contain certain
provisions relating to the limitation of liability and indemnification of
directors and officers. The Company's Certificate of Incorporation provides
that
 
                                      67
<PAGE>
 
directors of the Company may not be held personally liable to the Company or
its stockholders for monetary damages for a breach of fiduciary duty, except
for liability (i) for any breach of the director's duty of loyalty to the
Company or its stockholders, (ii) for acts or omissions not in good faith or
which involve intentional misconduct or a knowing violation of the law, (iii)
under Section 174 of the Delaware General Corporation Law, relating to
prohibited dividends, distributions and repurchases or redemptions of stock, or
(iv) for any transaction from which the director derives an improper personal
benefit. However, such limitation does not limit the availability of non-
monetary relief in any action or proceeding against a director. In addition,
the Company's Certificate of Incorporation and Bylaws provide that the Company
shall indemnify its directors and officers to the fullest extent authorized by
Delaware law.
 
 Classified Board of Directors
 
  Upon completion of this offering, the Company's Certificate of Incorporation
will provide that, so long as the Board of Directors consists of more than two
directors, the Board of Directors will be divided into three classes of
directors serving staggered three-year terms. As a result, one-third of the
Company's Board of Directors will be elected each year.
 
 No Stockholder Action by Written Consent
 
  Upon completion of this offering, the Company's Certificate of Incorporation
will provide that the stockholders can take action only at a duly called annual
or special meeting of Stockholders. Stockholders of the Company will not be
able to take action by written consent in lieu of a meeting. These provisions
may have the effect of deterring hostile takeovers or delaying changes in
control or management of the Company.
 
TRANSFER AGENT AND REGISTRAR
   
  ChaseMellon Shareholder Services LLC has been appointed as the transfer agent
and registrar for the Company's Common Stock. Its telephone number for such
purposes is (212) 553-9730.     
 
                                       68
<PAGE>
 
                               RESCISSION OFFERS
 
  The Company intends to commence approximately 30 days after the
effectiveness of the Offering made hereby, a rescission offer (the "Rescission
Offer") pursuant to a registration statement filed under the Securities Act of
1933, as amended (the "Act") and pursuant to the state securities laws of the
States of California, Florida, Illinois, Missouri, Kentucky, Texas, and
Wisconsin, covering convertible debentures and Common Stock sold to investors
which may have been sold in violation of the registration requirements of the
federal and state securities laws, which represent an aggregate of 105,828
shares as of June 30, 1997 (the "Rescission Stock"). Because of the frequency
and number of sales, including the number of persons who received offers and
who purchased shares, the private placement exemption under the Act may not
have been available for the Company's prior sales of the Rescission Stock. The
Company will offer to rescind such prior sales by repurchasing the Rescission
Stock at the price per share paid therefor (a range of $3.75 per share to
$30.00 per share) plus interest thereon at the statutory rate as the case may
be from the date of purchase by the purchaser to the expiration of the
Rescission Offer. The Company currently expects to use a portion of the
proceeds from the offering to make such payments, if any. The Rescission Offer
will expire approximately 30 days after the effectiveness of the registration
statement with respect to the Rescission Stock. Under such Rescission Offer,
the Company would be required to make an aggregate payment of approximately
$1.4 million plus the aggregate amount of interest thereon as described above,
if all offerees accept the offer. Offerees who do not accept the Rescission
Offer will, for purposes of applicable federal and state securities laws, be
deemed to hold registered shares under the Act which will be freely tradeable
in the public market as of the effective date of the registration statement
with respect to the Rescission Stock. The Act does not expressly provide that
a Rescission Offer will terminate a purchaser's right to rescind a sale of
stock which was not registered under the Act as required. Accordingly, should
the Rescission Offer be rejected by any or all offerees, the Company may
continue to be contingently liable under the Act for the purchase price of
Rescission Stock up to an aggregate amount of approximately $1.4 million plus
statutory interest of approximately $300,000.
 
  In addition, options issued pursuant to the Company's 1995 Stock Incentive
Plan for Employees and Consultants (the "1995 Plan") and nonplan options for
the purchase of Common Stock were issued to approximately 150 to 200 people in
California in 1995 and 1996 for which the Company was unable to rely on the
exemption provided by Section 25102(f) of the California Corporations Code. In
March 1996, the Company was denied a permit for these issuances by the
California Commissioner of Corporations as a result of the Company's having
had two classes of Common Stock with differing voting rights. In addition, a
smaller number of options were issued to optionees in other states, including
Michigan, Missouri, Virginia, Washington and Florida, for which the Company
may not have had available an exemption from qualification. Also, the November
17, 1995, grant of options for the purchase of 60,000 shares of Common Stock
to employees of Critical Technologies Incorporated was not qualified and may
not have had an exemption available under the blue sky laws of California. The
aforementioned options are potentially subject to rescission, and the Company
intends to include them in its planned Rescission Offer discussed above. Under
such Rescission Offer, the Company could be required to make an aggregate
payment of up to approximately $940,000. The Company currently expects to use
a portion of the proceeds from the offering to make such payments, if any.
 
  As of the date hereof, management is not aware of any claims for rescission
against the Company. While the Company will offer to rescind the securities
sales, there are no assurances that the Company will not otherwise be subject
to possible penalties or fines relating to these issuances. The Company
believes the Rescission Offers will provide it with additional meritorious
defenses to any such future claims. See "Risk Factors--Rescission Offers,"
"Use of Proceeds," "Shares Eligible for Future Sale" and Note 5 of Notes to
the Financial Statements.
 
                        SHARES ELIGIBLE FOR FUTURE SALE
   
  Upon completion of this offering, the Company will have approximately
12,804,838 shares of Common Stock outstanding, after giving effect to the
automatic conversion of all outstanding shares of Preferred Stock into Common
Stock immediately prior to the closing of this offering and the repurchase by
the Company of certain shares from certain stockholders who are not officers,
directors or affiliates of the Company at the per share Price to Public, and
    
                                      69
<PAGE>
 
assuming (i) no exercise of the Underwriters' over-allotment option, and (ii)
no exercise of outstanding options or warrants. Effective upon the
consummation of this offering, assuming no exercise of outstanding options or
warrants, the Company will have outstanding options to purchase approximately
1,869,907 shares of Common Stock and warrants to purchase an aggregate of
approximately 1,590,540 shares of Common Stock.
   
  Of the Common Stock outstanding upon completion of this offering, the
3,600,000 shares of Common Stock sold in this offering will be freely
tradeable without restriction or further registration under the Securities
Act, except for any shares purchased by "affiliates" of the Company, as that
term is defined under the Securities Act and the Regulations promulgated
thereunder (an "Affiliate"). The remaining 9,204,838 shares of Common Stock
held by officers, directors, employees, consultants and other stockholders of
the Company were sold by the Company in reliance on exemptions from the
registration requirements of the Securities Act and are "restricted
securities" within the meaning of Rule 144 under the Securities Act. Any
shares of Common Stock issued upon the exercise of options or warrants held by
any of such persons will constitute restricted securities. Approximately
178,114 of the outstanding shares of Common Stock that are restricted
securities will be eligible for sale in the public market as of the date of
this Prospectus (the "Effective Date") in reliance on Rule 144(k) under the
Securities Act. The remaining 9,026,724 shares of Common Stock held by
existing stockholders are subject to lock-up agreements with the
Representatives. Of the shares of Common Stock subject to lock-up agreements,
approximately 7,600,193 shares may not be sold or transferred until 360 days
after the Effective date, approximately 1,295,627 shares may not be sold or
transferred until 180 days after the Effective Date and approximately 126,105
shares may not be sold or transferred until 90 days after the Effective Date.
None of the shares subject to such lock-up agreements may be sold or
transferred during the applicable lock-up period without the consent of the
underwriters except for transfers pursuant to gifts or certain partnership
distributions and similar transfers in which the transferee enters into a
substantially similar lock-up agreement. Upon the expiration of the lock-up
agreements, all of such locked-up shares will become eligible for sale either
360, 180 or 90 days, respectively, after the Effective Date subject to the
provisions of Rules 144(k), 144 or 701. UBS Securities LLC may, in its sole
discretion and at any time without notice, release all or any portion of the
securities subject to these lock-up agreements.     
 
  In general, under Rule 144 as currently in effect, a person (or persons
whose shares are aggregated), including an Affiliate, who has beneficially
owned restricted securities for a period of at least one year from the later
of the date such restricted securities were acquired from the Company or the
date they were acquired from an Affiliate, is entitled to sell, within any
three-month period commencing 90 days after the Effective Date, a number of
shares that does not exceed the greater of 1% of the then outstanding shares
of Common Stock (approximately 4,800 shares immediately after this offering)
or the average weekly trading volume in the Common Stock during the four
calendar weeks preceding such sale. Sales under Rule 144 are also subject to
certain provisions relating to the number and notice of sale and the
availability of current public information about the Company.
 
  Further, under Rule 144(k), if a period of at least two years has elapsed
between the later of the date restricted securities were acquired from the
Company and the date they were acquired from an Affiliate of the Company, a
holder of such restricted securities who is not an Affiliate at the time of
the sale and has not been an Affiliate for at least three months prior to the
sale would be entitled to sell the shares immediately after the Effective Date
without regard to the volume and manner of sale limitations described above.
Any employee, director or consultant to the Company who purchased his or her
shares pursuant to a written compensation plan or contract is entitled to rely
on the resale provisions of Rule 701, which permits non-Affiliates to sell
their Rule 701 shares beginning 90 days after the Effective Date without
having to comply with the volume limitations and other restrictions of Rule
144 and permits Affiliates to sell their Rule 701 shares without having to
comply with the Rule 144 holding period restrictions. As of June 30, 1997,
there were outstanding options to purchase approximately 1,548,507 shares
which under certain circumstances would be available for sale pursuant to Rule
701, of which approximately 1,465,167 of the shares underlying such options
are subject to lock-up agreements. Of the approximately 1,869,907 total shares
issuable upon exercise of outstanding options, approximately 1,628,027 shares
may not be sold or transferred until 360 days after the Effective Date,
approximately 158,540 shares may not be sold or transferred until 180 days
after the Effective Date, and approximately 83,340 shares may not be sold or
transferred until 90 days after the Effective Date. Options for approximately
706,635 of the total 1,563,907 shares will be exercisable as of June 30, 1997.
 
                                      70
<PAGE>
 
  In addition, the Company intends to register shares of Common Stock reserved
for issuance pursuant to its 1993 Incentive Stock Option Plan, 1995 Stock
Incentive Plan for Employees and Consultants, Amended and Restated 1996 Stock
Plan, 1997 Stock Plan and 1997 Employee Stock Purchase Plan following the
closing of this offering. Shares issued under the 1997 Stock Plan and 1997
Employee Stock Purchase Plan (other than shares issued to the Affiliates)
after the effective date of a registration statement covering such shares
generally may be sold immediately in the public market, subject to vesting
requirements and the lock-up agreements described above. See "Management--
Employee Stock Plans."
 
  Prior to this offering, there has been no public market for the Common Stock
of the Company, and any sale of substantial amounts of Common Stock in the
open market, or the availability of shares for sale, may adversely affect the
market price of the Common Stock and the ability of the Company to raise funds
through equity offerings in the future.
 
  The holders of approximately 7.3 million shares are entitled to certain
registration rights with respect to their shares. See "Description of Capital
Stock--Registration Rights."
 
                                      71
<PAGE>
 
                                 UNDERWRITING
 
  Subject to the terms and conditions of the Underwriting Agreement, the
underwriters named below (the "Underwriters"), for whom UBS Securities LLC,
Unterberg Harris and Wheat, First Securities, Inc. are acting as
representatives (the "Representatives"), have agreed to purchase from the
Company the following respective number of shares of Common Stock:
 
<TABLE>   
<CAPTION>
                                                                    TOTAL NUMBER
   UNDERWRITERS                                                      OF SHARES
   ------------                                                     ------------
   <S>                                                              <C>
   UBS Securities LLC..............................................
   Unterberg Harris................................................
   Wheat, First Securities, Inc. ..................................
                                                                     ---------
     Total.........................................................  3,600,000
                                                                     =========
</TABLE>    
 
  The Underwriting Agreement provides that the obligations of the Underwriters
are subject to certain conditions precedent, including the absence of any
material adverse change in the Company's business and the receipt of certain
certificates, opinions and letters from the Company and its counsel. The
nature of the Underwriters' obligations is such that they are committed to
purchase all shares of Common Stock offered hereby if any of such shares are
purchased. The Company has agreed to indemnify the Underwriters against
certain liabilities, including liabilities under the Securities Act.
 
  The Representatives have advised the Company that the Underwriters propose
to offer the shares of Common Stock directly to the public at the offering
price set forth on the cover page of this Prospectus, and to certain dealers
at such price less a commission not in excess of $   per share. The
Underwriters may allow and such dealers may reallow a concession not in excess
of $   per share to certain other dealers. After the public offering of the
shares of Common Stock, the offering price and other selling terms may be
changed by the Underwriters.
 
  The Representatives have further advised the Company that, pursuant to
Regulation M under the Securities Act, certain persons participating in the
offering may engage in transactions, including stabilizing bids, syndicate
covering transactions or the imposition of penalty bids, which may have the
effect of stabilizing or maintaining the market price of the Common Stock at a
level above that which might otherwise prevail in the open market. A
"stabilizing bid" is a bid for or the purchase of the Common Stock on behalf
of the Underwriters for the purpose of fixing or maintaining the price of the
Common Stock. A "syndicate covering transaction" is the bid for or the
purchase of the Common Stock on behalf of the Underwriters to reduce a short
position incurred by the Underwriters in connection with the offering. A
"penalty bid" is an arrangement permitting the Representatives to reclaim the
selling concession otherwise accruing to an Underwriter or syndicate member in
connection with the offering if the Common Stock originally sold by such
Underwriter or syndicate member is purchased by the Representatives in a
syndicate covering transaction and has therefore not been effectively placed
by such Underwriter or syndicate member. The Representatives have advised the
Company that such transactions may be effected on the Nasdaq National Market
or otherwise and, if commenced, may be discontinued at any time.
   
  The Company has granted to the Underwriters an option, exercisable no later
than 30 days after the date of this Prospectus, to purchase up to 540,000
additional shares of Common Stock to cover over-allotments, if any, at the
public offering price set forth on the cover page of this Prospectus, less the
underwriting discounts and commissions. To the extent that the Underwriters
exercise this option, each of the Underwriters will have a firm commitment to
purchase approximately the same percentage thereof which the number of shares
of Common Stock to be purchased by it shown in the above table bears to the
total number of shares of Common Stock offered hereby. The Company will be
obligated, pursuant to the option, to sell such shares to the Underwriters.
    
                                      72
<PAGE>
 
  All officers, directors and significant stockholders of the Company who
beneficially own or have dispositive power over substantially all of the
shares of Common Stock outstanding prior to this offering, have agreed that
they will not, without the prior written consent of the Representatives,
offer, sell, contract to sell, pledge, grant any option to sell or otherwise
dispose of shares of Common Stock or securities convertible, or exchangeable
for, Common Stock, or warrants or other rights to purchase shares of Common
Stock, whether now owned or hereafter acquired, for a period of 360 days after
the date of this Prospectus. The Company has agreed that it will not, without
the prior written consent of lead managing underwriter, offer, sell or
otherwise dispose of any shares of Common Stock, for a period of 360 days
after the date of this Prospectus, except that the Company may grant
additional options and issue stock under its stock option plans and stock
purchase plans or issue shares of Common Stock upon the exercise of
outstanding stock options.
 
  The Representatives have advised the Company that the Underwriters do not
intend to confirm sales to any accounts over which they exercise discretionary
authority in excess of 5% of the number of shares of Common Stock offered
hereof.
 
  Concurrently with the closing of the offering, certain strategic investors
have agreed to purchase directly from the Company shares of Common Stock
having an aggregate purchase price of approximately $18.0 million (including
$3.0 in cancellation of indebtedness). The Representatives will receive a
commission payable by the Company on the sale of the shares related to the
Direct Placements equal to one-half of the underwriting discounts and
commissions payable on the shares offered in the offering. All of the shares
purchased in the Direct Placements will be purchased at the Price to Public
set forth on the cover page of this Prospectus. See "Direct Placements" and
"Certain Transactions--Williams Transaction."
 
  Prior to this offering, there has been no public market for the Common Stock
of the Company. The initial public offering price will be determined through
negotiations among the Company and the Representatives. Among the factors to
be considered in determining the initial public offering price, in addition to
prevailing market and economic conditions, are certain financial information
of the Company, the history of, and the prospects for, the Company and the
industry in which it competes, an assessment of the Company's management, its
past and present operations, the prospects for, and timing of, future revenues
of the Company, the present stage of the Company's development and the above
factors in relation to market values and various valuation measures of other
companies engaged in activities similar to those of the Company. The initial
public offering price set forth on the cover page of this Prospectus should
not, however, be considered an indication of the actual value of the Common
Stock. Such price is subject to change as a result of market conditions and
other factors. There can be no assurance that an active trading market will
develop for the Common Stock or that the Common Stock will trade in the public
market subsequent to this offering at or above the initial offering price.
 
                                 LEGAL MATTERS
 
  The validity of the shares of Common Stock offered hereby will be passed
upon for the Company by Wilson Sonsini Goodrich & Rosati, Professional
Corporation, Palo Alto, California. Certain legal matters in connection with
the Common Stock offered hereby will be passed upon for the Underwriters by
Brobeck, Phleger & Harrison LLP, Palo Alto, California. Brobeck, Phleger &
Harrison LLP has represented the Company with respect to certain legal matters
and may continue to represent the Company from time to time.
 
                                    EXPERTS
 
  The financial statements of the Company as of December 31, 1995 and 1996 and
for each of the three years in the period ended December 31, 1996, appearing
in this Prospectus and Registration Statement have been audited by Ernst &
Young LLP, independent auditors, as set forth in their report thereon
appearing elsewhere herein, and are included in reliance upon such report
given upon the authority of such firm as experts in accounting and auditing.
 
                                      73
<PAGE>
 
                            ADDITIONAL INFORMATION
 
  A Registration Statement on Form S-1, including amendments thereto, relating
to the Common Stock offered hereby has been filed by the Company with the
Securities and Exchange Commission, Washington, D.C. This Prospectus does not
contain all of the information set forth in the Registration Statement and the
exhibits and schedules thereto. Statements contained in this Prospectus as to
the contents of any contract or other document referred to are not necessarily
complete and in each instance reference is made to the copy of such contract
or other document filed as an exhibit to the Registration Statement, each such
statement being qualified in all respects by such reference. For further
information with respect to the Company and the Common Stock offered hereby,
reference is made to such Registration Statement, exhibits and schedules. A
copy of the Registration Statement may be inspected by anyone without charge
at the Commission's principal office, 450 Fifth Street, N.W., Washington, D.C.
20549, and copies of all or any part thereof, including any exhibit thereto,
may be obtained from the Commission upon the payment of certain fees
prescribed by the Commission. The Commission maintains a World Wide Web site
that contains reports, proxy and information statements and other information
regarding registrants that file electronically with the Commission. The
address of the site is http://www.sec.gov.
 
  The Company intends to furnish its stockholders with annual reports
containing financial statements certified by its independent auditors and
quarterly reports for the first three quarters of each fiscal year containing
unaudited interim financial information.
 
                                      74
<PAGE>
 
                               GLOSSARY OF TERMS
 
56 Kbps....................  Equivalent to a single high-speed telephone
                             service line; capable of transmitting one voice
                             call or 56 Kbps of data. Currently in widespread
                             use by medium and large businesses primarily for
                             entry level high-speed data and very low-speed
                             video applications.
 
ATM........................  Asynchronous Transfer Mode. A low latency, fixed
                             delay information transfer standard for routing
                             traffic. The ATM format can be used by many
                             different information systems, including LANs, to
                             deliver traffic at varying rates, permitting a
                             mix of data, voice and video.
 
Backbone...................  A centralized high-speed network that
                             interconnects smaller, independent networks.
 
Bandwidth..................  The number of bits of information that can move
                             through a communications medium in given amount
                             of time; the capacity of a telecommunications
                             circuit/network to carry voice, data and video
                             information. Typically measured in Kbps and Mbps.
                             Bandwidth from public networks is typically
                             available to business and residential end-users
                             in increments from 56 Kbps to T-3.
 
CIR........................  Committed Information Rate. The rate, usually
                             expressed as a particular quantitative amount of
                             Kbps of Mbps of bandwidth, at which data is
                             guaranteed to be transmitted through a dedicated
                             lease line network connection.
 
CLEC.......................  Competitive local exchange carrier. A
                             telecommunications company that provides an
                             alternative to a LEC for local transport of
                             private line and special access
                             telecommunications services.
 
E-mail.....................  An application that allows a user to send or
                             receive text messages to or from any other user
                             with an Internet address, commonly termed an E-
                             mail address.
 
Firewall...................  A system placed between networks that filters
                             data passing through it and removes unauthorized
                             traffic, thereby enhancing the security of the
                             network.
 
Frame relay................  A variable delay information transfer standard
                             for relaying traffic. Frame relay can be an
                             economical means to backhaul traffic to an ATM
                             network.
 
FTP........................  File Transfer Protocol. A protocol that allows
                             file transfer between a host and a remote
                             computer.
 
Internet...................  A global collection of interconnected computer
                             networks which use TCP/IP, a common
                             communications protocol.
 
ISDN.......................  Integrated Services Digital Network. An
                             information transfer standard for transmitting
                             digital voice and data over telephone lines at
                             speeds up to 128 Kbps.
 
Kbps.......................  Kilobits per second. A transmission rate. One
                             kilobit equals 1,024 bits of information.
 
                                      G-1
<PAGE>
 
LAN........................  Local Area Network. A data communications network
                             designed to interconnect personal computers,
                             workstations, minicomputers, file servers and
                             other communications and computing devices within
                             a localized environment.
 
Latency....................  The time that elapses between the moment when a
                             command is sent to the time that a response is
                             received. On a network, latency is due to delays
                             in routers or switches, congestion delays on a
                             crowded backbone, and the time required for
                             electrons to travel a great distance between
                             nodes on a network.
 
Leased line................  Telecommunications line dedicated to a particular
                             customer along a predetermined route.
 
LEC........................  Local Exchange Carrier. A telecommunications
                             company that provides telecommunications services
                             in a geographic area in which calls generally are
                             transmitted without toll charges.
 
Mbps.......................  Megabits per second.
 
Modem......................  A device for transmitting digital information
                             over an analog telephone line.
 
NAP........................  Network Access Point. A location at which ISPs
                             exchange each other's traffic.
 
Online services............  Commercial information services that offer a
                             computer user access to a specified slate of
                             information, entertainment and communications
                             menus on what appears to be a single system.
 
Peering....................  The commercial practice under which nationwide
                             ISPs exchange each other's traffic without the
                             payment of settlement charges.
 
POPs.......................  Points-of-presence. Geographic areas within which
                             the Company provides local access. For purposes
                             of this Memorandum, POPs include both physical
                             points of presence as well as VLA.
 
Router.....................  A system placed between networks that relays data
                             to those networks based upon a destination
                             address contained in the data packets being
                             routed.
 
Server.....................  Software that allows a computer to offer a
                             service to another computer. Other computers
                             contact the server program by means of matching
                             client software. In addition, such term means the
                             computer on which server software runs.
 
SuperPOP...................  A SuperPOP is a Concentric POP that is directly
                             connected to the Concentric ATM backbone.
                             SuperPOPs typically support dial access from the
                             region surrounding the SuperPOP (typically within
                             200 miles of the SuperPOP) using the services of
                             a CLEC. SuperPOPs also support dedicated access
                             connections to customer locations using Local
                             Exchange Carrier and/or Competitive Access
                             Provider facilities to connect the customer to
                             the Concentric SuperPOP.
 
TCP/IP.....................  Transmission Control Protocol/Internet Protocol.
                             A suite of network protocols that allow computers
                             with different architectures and operating system
                             software to communicate with other computers on
                             the Internet.
 
T-1........................  A data communications circuit capable of
                             transmitting data at 1.5 Mbps.
 
T-3........................  A data communications circuit capable of
                             transmitting data at 45 Mbps.
 
UNIX.......................  A computer operating system frequently found on
                             workstations and PCs and noted for its
                             portability and communications functionality.
 
                                      G-2
<PAGE>
 
VLA........................  Virtual local access call numbers which allow a
                             subscriber in a location outside the calling area
                             of a physical POP to place a local call to a
                             phone number without incurring long distance or
                             message unit charges.
 
VPN........................  Virtual Private Network. A network capable of
                             providing the tailored services of a private
                             network (i.e., low latency, high throughput,
                             security and customization) while maintaining the
                             benefits of a public network (i.e., ubiquity and
                             economies of scale).
 
World Wide Web or Web......  A system that supports easy access to documents
                             that have been linked across the Internet. The
                             documents contain links to each other, hence the
                             term "Web." Users do not have to know the
                             locations of particular documents and work
                             through a user friendly interface.
 
Webserver..................  A server connected to the Internet from which
                             Internet users can obtain information.
 
 
                                      G-3
<PAGE>
 
                         CONCENTRIC NETWORK CORPORATION
 
                         INDEX TO FINANCIAL STATEMENTS
 
<TABLE>
<CAPTION>
                                                                           PAGE
                                                                           ----
<S>                                                                        <C>
Report of Ernst & Young LLP, Independent Auditors........................  F-2
Balance Sheets...........................................................  F-3
Statements of Operations.................................................  F-4
Statements of Common Stock Subject to Rescission and Stockholders' Equity
 (Deficit)...............................................................  F-5
Statements of Cash Flows.................................................  F-6
Notes to Financial Statements............................................  F-8
</TABLE>
 
                                      F-1
<PAGE>
 
               REPORT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS
 
  The Board of Directors Concentric Network Corporation
 
  We have audited the accompanying balance sheets of Concentric Network
Corporation as of December 31, 1995 and 1996, and the related statements of
operations, common stock subject to rescission and stockholders' equity
(deficit), and cash flows for each of the three years in the period ended
December 31, 1996. These financial statements are the responsibility of the
Company's management. Our responsibility is to express an opinion on these
financial statements based on our audits.
 
  We conducted our audits in accordance with generally accepted auditing
standards. Those standards require that we plan and perform the audit to
obtain reasonable assurance about whether the financial statements are free of
material misstatement. An audit includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements. An audit
also includes assessing the accounting principles used and significant
estimates made by management, as well as evaluating the overall financial
statement presentation. We believe that our audits provide a reasonable basis
for our opinion.
 
  Since the date of completion of our audit of the accompanying financial
statements and initial issuance of our report thereon dated March 14, 1997
which report contained an explanatory paragraph regarding the Company's
ability to continue as a going concern, the Company, as discussed in Note 1,
has obtained written representations from certain shareholders as to their
intent and ability to fund the operations of the Company through at least
December 31, 1997. Therefore, the conditions that raised substantial doubt
about whether the Company will continue as a going concern no longer exist.
 
  In our opinion, the financial statements referred to above present fairly,
in all material respects, the financial position of Concentric Network
Corporation at December 31, 1995 and 1996, and the results of its operations
and its cash flows for each of the three years in the period ended December
31, 1996, in conformity with generally accepted accounting principles.
                                             
                                          /s/ Ernst & Young LLP     
 
San Jose, California
March 14, 1997, except for Note 1--"The Company"
and Note 5, as to which the date is June 23, 1997,
   
and Note 10, as to which the date is July 30, 1997     
       
                                      F-2
<PAGE>
 
                         CONCENTRIC NETWORK CORPORATION
 
                                 BALANCE SHEETS
                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
 
<TABLE>
<CAPTION>
                                                                  PRO FORMA
                                                                STOCKHOLDERS'
                                 DECEMBER 31,                  EQUITY (DEFICIT)
                               ------------------   MARCH 31,    AT MARCH 31,
                                 1995      1996       1997           1997
                               --------  --------  ----------- ----------------
                                                   (UNAUDITED)   (UNAUDITED)
<S>                            <C>       <C>       <C>         <C>
           ASSETS
Current assets:
 Cash and cash equivalents...  $ 19,054  $ 17,657   $   2,841
 Accounts receivable, net of
  allowances including $80 in
  1996 and $303 in 1997 to a
  related party..............       116     1,849       2,323
 Prepaid expenses and other
  current assets.............     1,167     1,722       1,689
                               --------  --------   ---------
Total current assets.........    20,337    21,228       6,853
Property and equipment:
 Computer and telecommunica-
  tions equipment............    17,622    55,091      60,927
 Software....................       256       583         789
 Furniture and fixtures and
  leasehold improvements.....       833     2,130       2,612
                               --------  --------   ---------
                                 18,711    57,804      64,328
 Accumulated depreciation and
  amortization...............     2,422     9,877      11,101
                               --------  --------   ---------
                                 16,289    47,927      53,227
Other assets.................       609     1,567       1,358
                               --------  --------   ---------
Total assets.................  $ 37,235  $ 70,722   $  61,438
                               ========  ========   =========
LIABILITIES AND STOCKHOLDERS'
       EQUITY (DEFICIT)
Current liabilities:
 Accounts payable............  $  4,159  $ 16,723   $  15,619
 Accrued compensation and
  other employee benefits....       230       714         571
 Other current liabilities...       617     2,163       1,882
 Current portion of capital
  lease obligations, includ-
  ing $2,758 in 1995,$10,180
  in 1996, and $10,772 in
  1997 to a related party....     3,198    11,258      12,304
 Note payable to related par-
  ty.........................     3,000       --          --
 Deferred revenue............       141     1,238       1,182
                               --------  --------   ---------
Total current liabilities....    11,345    32,096      31,558
Capital lease obligations,
 including $10,210 in 1995,
 $29,167 in 1996, and $33,034
 in 1997 to a related party,
 net of current portion......    10,977    30,551      35,349
Convertible debentures.......        70       --          --
Commitments and contingencies
Class A common stock subject
 to rescission, $0.001 par
 value:
 Issued and outstanding
  shares--445 in 1995, 455 in
  1996 and 1997..............     5,080     5,150       5,150
Stockholders' equity (defi-
 cit):
 Preferred stock, $0.001 par
  value; issuable in series:
 Authorized shares--4,667 in
  1995 and 7,333 in 1996 and
  1997
 Issued and outstanding
  shares--2,170 in 1995,
  4,901 in 1996 and 1997;
  none outstanding pro
  forma--unaudited (liquida-
  tion preference of $89,798
  at March 31, 1997).........    35,695    95,215      96,323     $     --
 Common stock, $0.001 par
  value; issuable in clas-
  ses:
 Authorized shares--6,677 in
  1995, 13,343 in 1996 and
  1997
 Issued and outstanding
  shares--1,388 in 1995,
  1,393 in 1996 and 1,396 in
  1997; 6,411 shares issued
  and outstanding
  pro forma--unaudited.......     1,639     1,850       1,958        98,281
Accumulated deficit..........   (27,571)  (93,952)   (108,633)     (108,633)
Deferred compensation........       --       (188)       (267)         (267)
                               --------  --------   ---------     ---------
Total stockholders' equity
 (deficit)...................     9,763     2,925     (10,619)    $ (10,619)
                               --------  --------   ---------     =========
Total liabilities and stock-
 holders' equity (deficit)...  $ 37,235  $ 70,722   $  61,438
                               ========  ========   =========
</TABLE>
 
                            See accompanying notes.
 
                                      F-3
<PAGE>
 
                         CONCENTRIC NETWORK CORPORATION
 
                            STATEMENTS OF OPERATIONS
                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
 
<TABLE>
<CAPTION>
                                                             THREE-MONTHS
                              YEARS ENDED DECEMBER 31,      ENDED MARCH 31,
                              ---------------------------  ------------------
                               1994      1995      1996      1996      1997
                              -------  --------  --------  --------  --------
                                                              (UNAUDITED)
<S>                           <C>      <C>       <C>       <C>       <C>
Revenue...................... $   442  $  2,483  $ 15,648  $  1,533  $  9,154
Costs and expenses:
  Cost of revenue............   2,891    16,168    47,945     7,256    15,744
  Network equipment write-
   off.......................     --        --      8,321       --        --
  Development................     534       837     2,449       340     1,025
  Marketing and sales,
   including $95, $920,
   $2,448, $792, and $494 to
   a related party for the
   years ended December 31,
   1994, 1995, and 1996, and
   the three-month periods
   ended March 31, 1996 and
   1997, respectively........     639     3,899    16,609     3,120     4,936
  General and
   administrative............     611     2,866     3,445       736     1,060
                              -------  --------  --------  --------  --------
Total costs and expenses.....   4,675    23,770    78,769    11,452    22,765
                              -------  --------  --------  --------  --------
Loss from operations.........  (4,233)  (21,287)  (63,121)   (9,919)  (13,611)
Interest income..............     (19)     (137)     (614)     (192)     (129)
Interest expense, including
 $0, $797, $3,065, $506, and
 $1,061 to a related party
 for the years ended December
 31, 1994, 1995, and 1996,
 and the three-month periods
 ended March 31, 1996 and
 1997, respectively..........      76       858     3,874       653     1,199
                              -------  --------  --------  --------  --------
Net loss..................... $(4,290) $(22,008) $(66,381) $(10,380) $(14,681)
                              =======  ========  ========  ========  ========
Pro forma net loss per
 share.......................                    $ (11.92)           $  (1.98)
                                                 ========            ========
Shares used in computing pro
 forma net loss per share....                       5,567               7,398
                                                 ========            ========
</TABLE>
 
 
                            See accompanying notes.
 
                                      F-4
<PAGE>
 
                         CONCENTRIC NETWORK CORPORATION
 
   STATEMENTS OF COMMON STOCK SUBJECT TO RESCISSION AND STOCKHOLDERS' EQUITY
                                   (DEFICIT)
                                 (IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                    COMMON STOCK           STOCKHOLDERS' EQUITY (DEFICIT)               TOTAL
                                                     SUBJECT TO   ---------------------------------------------------  STOCK-
                                                     RESCISSION   PREFERRED STOCK  COMMON STOCK    ACCUMU-   DEFERRED HOLDERS'
                                                    ------------- ---------------- --------------   LATED    COMPEN-   EQUITY
                                                    SHARES AMOUNT SHARES   AMOUNT  SHARES  AMOUNT  DEFICIT    SATION  (DEFICIT)
                                                    ------ ------ ------- -------- ------  ------ ---------  -------- ---------
<S>                                                 <C>    <C>    <C>     <C>      <C>     <C>    <C>        <C>      <C>
Balance at December 31, 1993.................        --    $  --     --   $    --  1,339   $  101 $  (1,273)  $ --    $ (1,172)
 Issuance of Class A common stock............          7      200    --        --      5       19       --      --          19
 Issuance of stock for services..............        --       --     --        --      8       93       --      --          93
 Stock exchanged for long-term debt..........        --       --     --        --     31      348       --      --         348
 Contribution of shares in connection with
  note settlement............................        --       --     --        --    (66)     --        --      --         --
 Stock options granted for debt and
  services...................................        --       --     --        --    --       800       --      --         800
 Conversion of debentures to common stock....        241    2,612    --        --    --       --        --      --         --
 Net loss....................................        --       --     --        --    --       --     (4,290)    --      (4,290)
                                                     ---   ------ ------  -------- -----   ------ ---------   -----   --------
Balance at December 31, 1994.................        248    2,812    --        --  1,317    1,361    (5,563)    --      (4,202)
 Issuance of Series A preferred stock and
  common stock (net of issuance costs).......        --       --     906    10,147    62      117       --      --      10,264
 Issuance of Series C preferred stock (net of
  issuance costs)............................        --       --     805    20,691   --       --        --      --      20,691
 Conversion of note to Series B preferred
  stock......................................        --       --     367     4,035   --       --        --      --       4,035
 Warrants issued to purchase Series B
  preferred stock............................        --       --     --        822   --       --        --      --         822
 Issuance of Class A common stock............         23      690    --        --    --         1       --      --           1
 Issuance of Class A common stock for
  services...................................        --       --     --        --      2       19       --      --          19
 Conversion of officer's note payable for
  Class B common stock.......................        --       --     --        --      7       80       --      --          80
 Warrants issued to purchase Class A common
  stock......................................        --       --     --        --    --        61       --      --          61
 Conversion of debentures to Class A common
  stock......................................        174    1,578    --        --    --       --        --      --         --
 Net loss....................................        --       --     --        --    --       --    (22,008)    --     (22,008)
                                                     ---   ------ ------  -------- -----   ------ ---------   -----   --------
Balance at December 31, 1995.................        445    5,080  2,078    35,695 1,388    1,639   (27,571)    --       9,763
 Issuance of Class A common stock............        --       --     --        --    --         1       --      --           1
 Conversion of debentures to Class A common
  stock......................................         10       70    --        --    --       --        --      --         --
 Exercise of options.........................        --       --     --        --      5       22       --      --          22
 Conversion of note to Series C preferred
  stock (net of issuance costs)..............        --       --     123     2,960   --       --        --      --       2,960
 Issuance of Series D preferred stock (net of
  issuance costs)............................        --       --   2,451    48,533   --       --        --      --      48,533
 Conversion of note to Series D preferred
  stock......................................        --       --     249     5,072   --       --        --      --       5,072
 Warrants issued to purchase Series D
  preferred stock............................        --       --     --      2,955   --       --        --      --       2,955
 Deferred compensation resulting from grant
  of options.................................        --       --     --        --    --       188       --     (188)       --
 Net loss....................................        --       --     --        --    --       --    (66,381)    --     (66,381)
                                                     ---   ------ ------  -------- -----   ------ ---------   -----   --------
Balance at December 31, 1996.................        455    5,150  4,901    95,215 1,393    1,850   (93,952)   (188)     2,925
 Issuance of Class A common stock
  (unaudited)................................        --       --     --        --      3       11       --      --          11
 Warrants issued to purchase Series D
  preferred stock (net of issuance costs)
  (unaudited)................................        --       --     --      1,108   --       --        --      --       1,108
 Deferred compensation resulting from grant
  of options (unaudited).....................        --       --     --        --    --        97       --      (97)       --
 Amortization of deferred compensation
  (unaudited)................................        --       --     --        --    --       --        --       18         18
 Net loss (unaudited)........................        --       --     --        --    --       --    (14,681)    --     (14,681)
                                                     ---   ------ ------  -------- -----   ------ ---------   -----   --------
Balance at March 31, 1997 (unaudited)........        455   $5,150  4,901  $ 96,323 1,396   $1,958 $(108,633)  $(267)  $(10,619)
                                                     ===   ====== ======  ======== =====   ====== =========   =====   ========
</TABLE>
 
                            See accompanying notes.
 
                                      F-5
<PAGE>
 
                         CONCENTRIC NETWORK CORPORATION
 
                            STATEMENTS OF CASH FLOWS
                                 (IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                               THREE-MONTHS
                                YEARS ENDED DECEMBER 31,      ENDED MARCH 31,
                                ---------------------------  ------------------
                                 1994      1995      1996      1996      1997
                                -------  --------  --------  --------  --------
                                                                (UNAUDITED)
<S>                             <C>      <C>       <C>       <C>       <C>
OPERATING ACTIVITIES
Net loss......................  $(4,290) $(22,008) $(66,381) $(10,380) $(14,681)
Adjustments to reconcile net
 loss to net cash used in
 operating activities:
  Depreciation and
   amortization...............      169     2,196     7,528     1,261     3,629
  Amortization of deferred
   interest and marketing and
   sales related to issuance
   of warrants................      --        --      1,942        65       193
  Amortization of deferred
   compensation...............      --        --        --        --         18
  Loss on disposal of
   equipment..................      --         29       --        --        --
  Network equipment write-
   off........................      --        --      8,321       --        --
  Compensation related to
   stock sales and option
   grants.....................      400       864       --        --        --
  Stock issued for services...       93        19       --        --        --
  Changes in current assets
   and liabilities:
   Prepaid expenses and other
    current assets............      (48)     (818)      (57)     (114)       49
   Accounts receivable........      (81)      (14)   (1,734)     (301)     (474)
   Accounts payable...........    1,081     3,051     5,129       (75)      624
   Accrued compensation and
    other employee benefits...       57       173       484        32      (143)
   Deferred revenue...........      --        141     1,097       715       (57)
   Other current liabilities..      (20)      539     1,546       373      (282)
                                -------  --------  --------  --------  --------
Net cash used in operating
 activities...................   (2,639)  (15,828)  (42,125)   (8,424)  (11,124)
INVESTING ACTIVITIES
Additions of property and
 equipment....................     (791)   (1,427)   (6,889)     (514)   (2,495)
Increase in refundable
 deposits.....................      --        --       (442)      --        --
(Increase) decrease in note
 receivable...................     (255)      255       --        --        --
                                -------  --------  --------  --------  --------
Net cash used in investing
 activities...................   (1,046)   (1,172)   (7,331)     (514)   (2,495)
FINANCING ACTIVITIES
Proceeds from notes payable...      298     7,000     6,300       --        --
Repayment of lease obligations
 to a related party...........      --     (1,609)   (4,561)     (492)   (1,972)
Repayment of lease
 obligations..................      --        --       (886)      (88)     (344)
Repayment of notes payable....     (324)     (218)   (1,300)      --        --
Proceeds from sales of
 convertible debentures.......    3,500       --        --        --        --
Proceeds from issuances of
 stock and warrants...........      219    30,818    48,506      (211)    1,119
                                -------  --------  --------  --------  --------
Net cash provided by (used in)
 financing activities.........    3,693    35,991    48,059      (791)   (1,197)
                                -------  --------  --------  --------  --------
Increase (decrease) in cash
 and cash equivalents.........        8    18,991    (1,397)   (9,729)  (14,816)
Cash and cash equivalents at
 beginning of period..........       55        63    19,054    19,054    17,657
                                -------  --------  --------  --------  --------
Cash and cash equivalents at
 end of period................  $    63  $ 19,054  $ 17,657  $  9,325  $  2,841
                                =======  ========  ========  ========  ========
</TABLE>
 
                            See accompanying notes.
 
                                      F-6
<PAGE>
 
                         CONCENTRIC NETWORK CORPORATION
 
                     STATEMENTS OF CASH FLOWS--(CONTINUED)
                                 (IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                                THREE-MONTHS
                                    YEARS ENDED DECEMBER 31,   ENDED MARCH 31,
                                    ------------------------- -----------------
                                     1994     1995     1996     1996     1997
                                    ---------------- -------- -------- --------
                                                                 (UNAUDITED)
<S>                                 <C>     <C>      <C>      <C>      <C>
SUPPLEMENTAL DISCLOSURES OF
 NONCASH INVESTING AND FINANCING
 ACTIVITIES
Stock options issued to settle
 note payable.....................  $   400 $    --  $    --  $    --  $    --
Stock exchanged for notes payable,
 including accrued interest.......  $   348 $  4,115 $  8,082 $  3,010 $    --
Capital lease obligations incurred
 with a related party.............  $   --  $ 14,578 $ 30,945 $  2,485 $  6,435
Capital lease obligations
 incurred.........................  $   --  $  1,207 $  2,136 $    --  $    --
Reduction of accounts payable
 through capital lease obligations
 incurred.........................  $   --  $    --  $    --  $    --  $  1,726
Convertible debentures exchanged
 for stock........................  $ 2,612 $  1,578 $     70 $    --  $    --
Issuance of warrants..............  $   --  $    883 $  2,955 $    --  $    --
Purchase of property and equipment
 through accounts payable.........  $   --  $    --  $  6,344 $    --  $    --
SUPPLEMENTAL DISCLOSURES OF CASH
 FLOW INFORMATION
Interest paid.....................  $     9 $    850 $  2,807 $    401 $  1,156
</TABLE>
 
                            See accompanying notes.
 
                                      F-7
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                         NOTES TO FINANCIAL STATEMENTS
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
 
 The Company
 
  Concentric Network Corporation (the Company or Concentric) was incorporated
in the state of Florida in April 1991. Concentric provides tailored, value-
added Internet Protocol (IP) based network services for businesses and
consumers. To provide these services, the Company utilizes its low/fixed
latency, high-throughput network, employing its advanced network architecture
and the Internet. Concentric's service offerings for enterprises include
virtual private networks (VPNs), dedicated access facilities (DAFs) and Web
hosting services. These services enable enterprises to take advantage of
standard Internet tools such as browsers and high-performance servers for
customized data communications within an enterprise and between an enterprise
and its suppliers, partners and customers. These services combine the cost
advantages, nationwide access and standard protocols of public networks with
the customization, high performance, reliability and security of private
networks. Concentric's service offerings for consumers and small office/home
office customers include local Internet dial-up access, Web hosting services
and online multiplayer gaming.
 
  The accompanying financial statements have been prepared assuming that the
Company will continue as a going concern. Since inception, the Company has
incurred cumulative net losses of approximately $108,633,000 and has negative
working capital as of March 31, 1997. Management expects the Company to incur
additional losses and recognizes the need for an infusion of cash during the
fiscal year 1997. The Company is actively pursuing various alternatives to
secure additional financing and believes that sufficient funding will be
available to achieve its planned business objectives (see Note 10). The
Company has obtained written representations from certain shareholders as to
their intent and ability to fund operations through at least December 31,
1997.
 
 Interim Results
 
  The accompanying balance sheet as of March 31, 1997 and the statements of
operations and cash flows for the three months ended March 31, 1996 and 1997
and the statement of common stock subject to rescission and stockholders'
equity (deficit) for the three months ended March 31, 1997 are unaudited. In
the opinion of management, the statements have been prepared on the same basis
as the audited financial statements and include all adjustments, consisting of
normal recurring adjustments, necessary for the fair statement of interim
periods. The data disclosed in these notes to the financial statements for
these periods is also unaudited.
 
 Cash and Cash Equivalents
 
  The Company considers all highly liquid investments with an original
maturity (at date of purchase) of three months or less to be the equivalent of
cash for the purpose of balance sheet and statement of cash flows
presentation. Cash and cash equivalents are carried at cost which approximates
market value. There were no short-term investments at December 31, 1995 and
1996 or March 31, 1997.
 
 Property and Equipment
 
  Property and equipment are stated at cost. Depreciation and amortization are
provided using the straight-line method over the estimated useful lives of the
related assets as follows: computer and telecommunications equipment: three to
five years; purchased software: three to five years; furniture and fixtures:
eight to ten years; and leasehold improvements: the shorter of the remaining
term of the related leases or the estimated economic useful lives of the
improvements. Equipment under capital leases is amortized over the related
lease term (see Note 3).
 
 
                                      F-8
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
 Revenue and Customer Receivables
 
  Revenue is recognized over the period in which services are provided,
generally monthly. Payments received in advance of services being provided are
included in deferred revenues. Substantially all end-user subscribers pay for
services with major credit cards for which the Company receives daily
remittances from the credit card carriers.
 
  Commissions and other obligations to strategic partners through marketing
and distribution arrangements are expensed as incurred, at the time the
associated revenue is recognized.
 
 Concentration of Credit Risk
 
  The Company typically offers its enterprise customers credit terms. The
Company performs ongoing credit evaluations of its customers' financial
condition and generally does not require collateral. Credit losses have
historically been insignificant.
 
 Cost of Revenue
 
  Cost of revenue includes the cost of operating the Company's network,
including telecommunications charges, personnel costs, equipment depreciation
and amortization, and related overhead.
 
 Development
 
  Development expenditures primarily include personnel and related overhead
expenses incurred to design, create, and test product offerings and associated
client and server tools. These expenditures are charged to operations as
incurred. The Company does not currently develop software that is sold,
licensed, or otherwise marketed. Substantially all software development
efforts by the Company are in connection with the development of its network.
 
 Marketing and Sales
 
  Marketing and sales expense consists primarily of personnel expenses,
including salary and commissions, costs of marketing programs and the cost of
800 number circuits utilized by the Company for customer support functions.
 
 Advertising Costs
 
  The Company expenses the costs of advertising as incurred except for direct-
response advertising costs meeting certain specific criteria. To date, no
direct-response advertising costs have been capitalized.
 
 Income Taxes
 
  The Company accounts for income taxes using the liability method in
accordance with Financial Accounting Standards Board Statement No. 109,
"Accounting for Income Taxes".
 
 Use of Estimates
 
  The preparation of financial statements in conformity with generally
accepted accounting principles requires management to make estimates and
assumptions that affect the amounts reported in the financial statements and
accompanying notes. Actual results could differ from those estimates.
 
 
                                      F-9
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
 Net Loss Per Share (Historical)
 
  Except as noted below, net loss per share is computed using the weighted
average number of shares of common stock outstanding excluding common stock
subject to rescission. Common stock equivalent shares from convertible
preferred stock and from stock options and warrants are not included as the
effect is antidilutive. Pursuant to the Securities and Exchange Commission
Staff Accounting Bulletins, common and common equivalent shares issued by the
Company at prices below the initial public offering price during the twelve-
month period prior to the offering have been included in the calculation as if
they were outstanding for all periods presented (using the treasury stock
method and the estimated public offering price in calculating equivalent
shares).
 
  Per share information calculated on the above noted basis is as follows (in
thousands, except for per share amounts):
 
<TABLE>
<CAPTION>
                                   YEARS ENDED                THREE-MONTHS
                                  DECEMBER 31,               ENDED MARCH 31,
                          -------------------------------  --------------------
                            1994       1995       1996       1996       1997
                          ---------  ---------  ---------  ---------  ---------
<S>                       <C>        <C>        <C>        <C>        <C>
Net loss per share......  $   (2.18) $  (11.22) $  (32.85) $   (5.14) $   (7.25)
                          =========  =========  =========  =========  =========
Shares used in computing
 net loss per share.....  1,971,950  1,961,403  2,020,814  2,018,794  2,024,661
                          =========  =========  =========  =========  =========
</TABLE>
 
 Pro Forma Net Loss Per Share
 
  Pro forma net loss per share has been computed as described above and also
gives effect, even if antidilutive, to common equivalent shares from
convertible preferred shares that will automatically convert to common shares
upon the closing of the Company's initial public offering (using the as-if-
converted method).
 
 Stock-Based Compensation
 
  The Company accounts for employee stock option grants in accordance with
Accounting Principles Board Opinion No. 25, "Accounting for Stock Issued to
Employees" (APB Opinion No. 25), and has adopted the "disclosure only"
alternative described in Statement of Financial Accounting Standards No. 123,
"Accounting for Stock-Based Compensation" (FAS 123).
 
 Effect of New Accounting Standard
 
  In February 1997, the Financial Accounting Standards Board issued Statement
No. 128, "Earnings Per Share" (FAS 128), which is required to be adopted on
December 31, 1997. At that time, the Company will be required to change the
method currently used to compute earnings per share and to restate all prior
periods. Under the new requirements for calculating primary earnings per
share, the dilutive effect of stock options will be excluded. The impact of
FAS 128 on the calculation of primary and fully diluted earnings per share is
not expected to be material.
 
  The Company adopted Statement of Financial Accounting Standards No. 121,
"Accounting for the Impairment of Long-Lived Assets and for Long-Lived Assets
to be Disposed Of," effective January 1, 1996. The Company continually reviews
long-lived assets to assess recoverability based upon undiscounted cash flow
analysis. Impairments, if any, are recognized in operating results in the
period in which a permanent diminution in value is determined (see Note 3).
 
 Customer Concentrations
 
  The Company currently derives a substantial portion of its total revenue
from a single customer. For the year ended December 31, 1996 and the three
months ended March 31, 1997, revenue from WebTV Networks, Inc. represented
approximately 10.1% and 32.7%, respectively, of the Company's total revenue.
 
                                     F-10
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
 
2. NETWORK EQUIPMENT WRITE-OFF
 
  In December 1996, the Company wrote off approximately $8,321,000
representing the net book value and future commitments for certain network
equipment purchased from Sattel Communications LLC (Sattel), a stockholder of
the Company. The Company decided not to deploy the equipment in the network
because of concerns that the equipment would not provide the functionality and
reliability required by the Company and concerns that the equipment provider
would be unable to provide timely maintenance and support. Included in
accounts payable in the accompanying balance sheet at December 31, 1996 and
March 31, 1997 was $7,517,000 and $5,791,000, respectively, related to this
equipment.
 
3. COMMITMENTS
 
 Operating Leases
 
  The Company has an agreement with a third party through which such third
party makes available the premises at which the Company's POP sites throughout
the United States are located. POP sites are locations where certain
telecommunications switching and related equipment are installed. This
agreement expires in October 1999, and the amount of the payments is based,
among other things, on the number of POP sites maintained by the Company,
subject to certain minimums. Expenses of approximately $232,000, $1,155,000,
$1,622,000, $356,000, and $372,000 were incurred during the years ended
December 31, 1994, 1995, and 1996, and the three-month periods ended March 31,
1996 and 1997, respectively, for these facilities. Additionally, the Company
has agreements with three telecommunications companies to locate POP sites and
certain of such equipment at their facilities. The expiration dates associated
with these agreements range from December 1998 to January 2000. Expenses
incurred on these leases was $0 during 1996 and $162,000 for the three-month
period ended March 31, 1997.
 
  The Company leases space for offices and a data center in Bay City,
Michigan. The lease expires in December 1997. Rent expense associated with the
facility was approximately $36,000, $36,000, $42,000, $9,000, and $11,000 in
the years ended December 31, 1994, 1995, and 1996, and the three-month periods
ended March 31, 1996 and 1997, respectively. In March 1996, the Company
entered into a lease agreement for office space in Saginaw, Michigan,
primarily for its customer support organization. This lease expires in
December 2001. Rent expense associated with the Saginaw facility was
approximately $129,000 in 1996 and $54,000 for the three-month period ended
March 31, 1997. The Company maintains its corporate headquarters in Cupertino,
California where it leases its facility under an operating lease that expires
in April 1998. Lease expense associated with this facility was approximately
$100,000, $267,000, $61,000, and $200,000 in the years ended December 31, 1995
and 1996, and the three-month periods ended March 31, 1996 and 1997,
respectively.
 
  Rent expense under all operating leases of the Company totaled approximately
$268,000, $1,291,000, $2,060,000, $426,000, and $799,000 in the years ended
December 31, 1994, 1995 and 1996 and the three-month periods ended March 31,
1996 and 1997, respectively.
 
 
                                     F-11
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
  Future minimum lease commitments for all noncancelable operating leases at
December 31, 1996 are as follows (in thousands):
 
<TABLE>
       <S>                                                                <C>
       1997.............................................................. $2,283
       1998..............................................................    985
       1999..............................................................    779
       2000..............................................................    217
       2001..............................................................    217
                                                                          ------
       Total............................................................. $4,481
                                                                          ======
</TABLE>
 
 Capital Leases
 
  In August 1994, the Company entered into a master lease agreement under
which a related party began installing networking equipment at the Company's
POP sites and data center. This agreement became effective upon installation
and acceptance by the Company on March 31, 1995. The lease provides for
monthly payments for terms of 48 or 60 months, depending upon the type of
equipment. The Company has continued to install equipment under the terms of
this agreement, resulting in a monthly payment of approximately $896,000 and
$1,228,000 at December 31, 1996 and March 31, 1997, respectively.
 
  In September 1995, the Company entered into a master lease agreement with a
third party for an equipment lease line against which the Company has leased
approximately $3,342,000 as of March 31, 1997. The term of the lease is 36
months and provides for monthly payments of approximately $114,000 as of March
31, 1997. The Company has granted to the third party a security interest in
all equipment leased under this agreement.
 
  Assets capitalized under capital leases totaled approximately $15,785,000,
$48,856,000, and $52,885,000 at December 31, 1995 and 1996, and March 31,
1997, respectively, and are included in computer and telecommunications
equipment. Accumulated amortization for assets capitalized under capital
leases totaled approximately $1,787,000, $8,306,000, and $9,055,000 at
December 31, 1995 and 1996, and March 31, 1997 respectively. Amortization of
leased assets is included in depreciation and amortization expense. Future
minimum lease payments under capital lease obligations at December 31, 1996
are as follows (in thousands):
 
<TABLE>
       <S>                                                              <C>
       1997............................................................ $15,732
       1998............................................................  15,105
       1999............................................................  11,321
       2000............................................................   6,069
       Thereafter......................................................   3,393
                                                                        -------
       Total minimum lease payments....................................  51,620
       Less amount representing interest...............................   9,811
                                                                        -------
       Present value of net minimum lease payments.....................  41,809
       Less current portion of capital leases..........................  11,258
                                                                        -------
       Long-term portion of capital leases............................. $30,551
                                                                        =======
</TABLE>
 
 
                                     F-12
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
 Other
 
  The Company has a noncancelable service agreement with AT&T for the
utilization of its frame relay telecommunications network. The agreement
provides for minimum payments to AT&T of approximately $300,000 per month over
its three-year term, expiring in June 1999.
 
  The Company has a noncancelable service agreement with MCI for the
utilization of its ATM telecommunications network. The agreement provides for
minimum payments to MCI of approximately $1,200,000 per year over its term,
expiring three years after the end of an initial ramp up period but no later
than June 2000. The Company also has a noncancelable telecommunications
service agreement with MCI for other services, including dedicated access and
800 service, that provides for minimum payments of approximately $8,500,000
over the term of the agreement, expiring in June, 1998. The Company had
incurred expenses of approximately $3,700,000, $0, and $3,994,000 for the year
ended December 31, 1996 and the three-month periods ended March 31, 1996 and
1997, respectively, related to these other services.
 
  The Company has remaining minimum prepaid royalty commitments to a vendor
for distribution of licenses of the vendor's software totaling approximately
$1,016,000 due in installments through 1997. Prepaid royalties related to this
agreement were $300,000 at December 31, 1996 and $225,000 at March 31, 1997.
 
  In November 1995, the Company entered into a two-year service agreement
under which a third party provides substantially all of the network analysis
and deployment and maintenance of POP sites. This agreement has subsequently
been extended to October 31, 1999. The Company will reimburse the third party
for its employee compensation and direct costs for services provided. At the
end of the agreement, the third party is obligated to transfer to the Company
those personnel, resources, and facilities used to support the Company's
network analysis, POP site deployment, and maintenance. The Company, in turn,
will pay the third party $675,000 to relocate the remainder of the third
party's business to new facilities. Additionally, as part of the agreement,
the Company granted 60,000 options for its Class A common stock to employees
of such third party at an exercise price of $3.75. At March 31, 1997, all of
these options were vested.
 
4. CONVERTIBLE DEBENTURES AND NOTES
 
  At December 31, 1995, convertible debentures in the amount of $70,000,
representing 9,802 shares of common stock, were outstanding. The conversion of
these debentures into shares of Class A common stock subject to rescission was
completed in March 1996.
 
  In 1995, the Company issued convertible notes totaling $7,000,000 to
shareholders of which $4,000,000, plus accrued interest, was converted into
Series B convertible preferred stock in December 1995. The remaining
$3,000,000 outstanding at December 31, 1995 was converted into Series C
convertible preferred stock in February 1996.
 
5. COMMON STOCK SUBJECT TO RESCISSION
 
  In August 1993, the Company commenced sales of convertible debentures and
certain additional shares of its common stock. Through March 31, 1995, sales
of convertible debentures aggregated $4,260,000, and issuance of common stock
aggregated $890,000. The sale of common stock and sale of and/or conversion of
debentures into common stock was not made pursuant to a registration statement
filed under the Securities Act of 1933 (the Act) or any filings pursuant to
the laws of any of the states in which such sales occurred (State Blue Sky
Laws). Although at the time the Company believed the sale and conversion, if
applicable, of these securities was exempt from the provisions of the Act and
applicable State Blue Sky Laws, it appears that the appropriate exemptions may
not
 
                                     F-13
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
have been available. As a result, the Company is conducting a Recission Offer
and purchasers of these securities will be entitled to a return of the
consideration paid for their stock or debentures. As such, these shares have
been classified as common stock subject to rescission in the accompanying
financial statements. Additionally, options issued pursuant to the Company's
1995 Stock Incentive Plan to Employees and Consultants (the 1995 Plan) and
non-plan options were issued in various states for which the Company may not
have had an available exemption under state laws. Such options are potentially
subject to rescission and the Company intends to include them in the
rescission offer. As of March 31, 1997, there have been no claims asserted
against the Company. Subsequent to March 31, 1997, an analysis was performed
of the statutes of limitations under federal and state securities laws
applicable to the shares which may have been issued without securities laws
exemptions and it was determined that a number of such statute of limitations
had lapsed. While the Company will offer to rescind the shares and options
pursuant to the Rescission Offer, there can be no assurances that the Company
will not otherwise be subject to possible statutory remedies for return of the
purchase price of such securities plus interest thereon totaling, as of June
23, 1997, approximately $1,700,000 related to the issuance of the stock and an
amount equal to approximately $940,000 with respect to options.
 
6. STOCKHOLDERS' EQUITY
 
  On August 5, 1996, the Company amended its Articles of Incorporation to
increase the number of authorized shares of Class A common stock and preferred
stock to 13,333,333 and 7,333,333, respectively. Of the 7,333,333 authorized
shares of preferred stock, 1,000,000, 866,667, 933,333, and 4,533,333 are
designated as Series A, B, C, and D, respectively.
 
 Preferred Stock
 
  Preferred stock at December 31, 1996 is as follows:
 
<TABLE>
<CAPTION>
                                        SHARES
                                      ISSUED AND   PAR               LIQUIDATION
                           AUTHORIZED OUTSTANDING VALUE    AMOUNT    PREFERENCE
                           ---------- ----------- ------ ----------- -----------
<S>                        <C>        <C>         <C>    <C>         <C>
Series A convertible...... 1,000,000     906,454  $0.001 $10,146,987 $10,000,000
Series B convertible......   866,667     366,946  $0.001   4,857,130   4,035,130
Series C convertible......   933,333     928,243  $0.001  23,651,008  20,690,804
Series D convertible...... 4,533,333   2,699,588  $0.001  56,559,871  55,071,586
                                       ---------         ----------- -----------
                                       4,904,136         $95,214,996 $89,797,520
                                       =========         =========== ===========
</TABLE>
 
  In April 1995, the Company agreed to sell 906,454 shares of Series A
convertible preferred stock and, as discussed below, warrants to purchase
Class A common stock for an aggregate of $10,000,000. In December 1995,
convertible notes totaling $4,000,000 and accrued interest were converted into
366,946 shares of Series B convertible preferred stock (see Note 4). In
October 1995, the Company agreed to sell 928,243 shares of Series C
convertible preferred stock. In August 1996, the Company agreed to sell
2,699,588 shares of Series D convertible preferred stock and, as discussed
below, warrants to purchase 795,051 shares of Series D convertible preferred
stock in connection with other agreements established with certain Series D
investors. Included in the sale of Series D shares was the conversion of a
June 1996 $5,000,000 bridge loan and accrued interest thereon.
 
  The Preferred Stock and Warrant Purchase Agreement pursuant to which the
Series A convertible preferred stock was issued, as amended through August 21,
1996 (the Series A Agreement), contains certain provisions relating to
corporate governance prior to completion of a Qualified Public Offering, as
defined and as amended (see Note 10). These provisions include limiting the
size of the Company's Board of Directors to five, giving investors the right
to designate certain directors for election by the Company, and the automatic
designation for election of the Chief Executive Officer of the Company.
 
 
                                     F-14
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
  The Series D Preferred Stock Purchase Agreement (the Series D Agreement)
also contains certain provisions relating to corporate governance, which are
effective as long as 20% of the shares of Series D preferred stock issued at
the initial closing remain outstanding. These provisions include a requirement
that the Board of Directors be large enough to enable the Series D holders to
designate three, four, or five board members, depending on the number of
Series D shares outstanding.
 
  In addition, the Series A Agreement and the Series D Agreement provide that
without approval of the Series A and Series D investors, the Company may not
declare or pay dividends on common stock other than in common stock, make
loans or advances to any person except in the ordinary course of business or
under terms of a board-approved employee stock or option plan, or engage in a
transaction with an officer or director on terms better than could be obtained
from arms' length negotiations with an unrelated third party.
 
  Each share of Series A, B, C, and D convertible preferred stock is
convertible into shares of Class A common stock initially on a one-for-one
basis, subject to adjustment for, among other things, stock splits, stock
dividends, and the issuance of additional shares of common stock and
securities convertible into common stock. Additionally, each share of Series A
convertible preferred stock is convertible into .003207 shares of Class B
common stock. The conversion price of Series A, B, C, and D convertible
preferred stock is subject to adjustment for any future issuance of common
stock at a per share price less than the exercise or conversion price. Holders
of each share of Series A, B, C, and D convertible preferred stock are
entitled to the number of votes equal to the number of shares of Class A and
Class B common stock into which the preferred stock is convertible. Holders of
Series A, B, C, and D convertible preferred stock will be entitled to receive
dividends on a pari passu basis.
 
  Each share of Series A, B, C, and D convertible preferred stock will be
converted automatically into the number of shares of Class A common stock into
which such shares are convertible, immediately prior to the closing of a sale
of the Company's common stock to the public in a Qualified Public Offering, as
defined and as amended.
 
  In the event of liquidation, dissolution, or winding up of the Company, each
holder of Series A, B, C, and D convertible preferred stock will be entitled
to be paid, with respect to each share of Series A, B, C, and D convertible
preferred stock held, a liquidation preference out of the assets available for
distribution to shareholders in an amount equal to $11.03, $11.00, $27.30, and
$20.40, respectively. Thereafter, holders of common stock will get pro rata
shares of an amount equal to the aggregate liquid amounts paid to Series A, B,
C, and D. Any residual assets will be distributed among the holders of common
and preferred stock as if each share of convertible preferred stock had been
converted into the number of shares of common stock issuable upon conversion
of the convertible preferred stock immediately prior to such liquidation,
dissolution, or winding up of the Company.
 
 Warrants to Purchase Preferred Stock
 
  In connection with a customer network services arrangement, the Company
issued warrants to purchase 136,407 shares of Series B convertible preferred
stock at an exercise price of $11.00 beginning December 11, 1995 and warrants
to purchase 128,205 shares of Series B convertible preferred stock at an
exercise price of $27.30 beginning February 27, 1996. The warrants expire at
the earlier of October 1998 or ten days from the closing of a Qualified Public
Offering of the Company's common stock meeting certain criteria. In 1995, the
Company recorded deferred sales and marketing expense of $822,000 to reflect
the value of these warrants as determined by using the Black-Scholes option
pricing method. Amortization of deferred sales and marketing expense totaled
$249,000 for the year ended December 31, 1996, and $43,000 and $69,000 for the
three-month periods ended March 31, 1996 and 1997, respectively.
 
 
                                     F-15
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
  In December 1995, the Company issued warrants to purchase 181,876 shares of
Series B convertible preferred stock to certain preferred shareholders in
connection with the Series B convertible preferred stock financing. The
warrants expire three years from issuance and are exercisable at $11.00 per
share.
 
  On June 6, 1996 and July 29, 1996, the Company received bridge loans from
various investors of $5,000,000 and $1,300,000, respectively. Included in
these transactions were the issuance of warrants to purchase 36,765 shares and
63,725 shares of Series D convertible preferred stock. These warrants expire
three years from issuance and are exercisable at $20.40 per share. The value
of these warrants, approximately $330,000, was expensed as a cost of
financing.
 
  As part of the sale of Series D convertible preferred stock in August 1996,
the Company issued warrants to purchase 795,051 shares of Series D convertible
preferred stock to certain Series D investors. These warrants were issued in
connection with distribution, lease financing, and joint sales and marketing
agreements. These warrants will expire in three years and are exercisable at
$20.40 per share. The value of these warrants was determined by using the
Black-Scholes option pricing method. Approximately $1,369,000 and $121,000 of
this value was expensed in the year ended December 31, 1996 and the three-
month period ended March 31, 1997, respectively, with the remaining balance
being amortized over the three-year life of the warrants.
 
  Also, in connection with the sale of Series D convertible preferred stock,
an additional 176,678 warrants to purchase Series D convertible preferred
stock were issued for net consideration of approximately $1,108,000 in March
1997. These warrants will expire in three years and are exercisable at $20.40
per share.
 
 Common Stock
 
  Common stock at December 31, 1996 is as follows:
 
<TABLE>
<CAPTION>
                                              SHARES ISSUED
                                                   AND
                                   AUTHORIZED  OUTSTANDING  PAR VALUE   AMOUNT
                                   ---------- ------------- --------- ----------
   <S>                             <C>        <C>           <C>       <C>
   Class A........................ 13,333,333   1,385,790    $0.001   $1,769,819
   Class B........................     10,024       7,117    $0.001       80,065
                                   ----------   ---------             ----------
                                   13,343,357   1,392,907             $1,849,884
                                   ==========   =========             ==========
</TABLE>
 
  The holders of Class A common stock are entitled to one vote per share on
all matters submitted to the shareholders. The holders of Class B common stock
are entitled to 500 votes per share on all matters submitted to the
shareholders. Each share of Class B common stock will automatically be
converted into one share of Class A common stock immediately prior to the
closing of common stock in a Qualified Public Offering, as defined and as
amended. The holders of common stock do not have preemptive rights under the
Company's Articles of Incorporation to subscribe for additional shares of
common stock. See Note 10 for the conversion of Class B common stock.
 
  Subject to the preferences of the preferred stock, the holders of common
stock are entitled to receive ratably such dividends, if any, as may be
declared from time to time by the Board of Directors out of funds legally
available for payment. In the event of the liquidation, dissolution, or
winding up of the Company, holders of common stock are entitled to receive
ratably an amount equal to the aggregate liquidation amount paid to all
holders of preferred stock. Thereafter, any remaining assets of the Company
are shared ratably by holders of common stock, calculated assuming the
conversion of all outstanding preferred stock.
 
 
                                     F-16
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
 Warrants to Purchase Common Stock
 
  From April 20 through July 5, 1995, the Company issued warrants to purchase
181,876 shares of Class A common stock to certain preferred shareholders in
connection with the Series A convertible preferred stock financing. The
warrants expire three years from issuance and are exercisable at $11.00 per
share.
 
  In connection with the capital lease agreements discussed in Note 3, the
Company issued warrants to purchase 67,388 shares of Class A common stock at
an exercise price of $3.75. The warrants expire over a term from July 20, 1998
to February 15, 2000. In 1995, the Company recorded deferred interest of
$61,000 to reflect the value of these warrants using the Black-Scholes option
pricing method. Amortization of deferred interest totaled $25,000 for the year
ending December 31, 1996 and $16,000 and $3,000 for the three-month periods
ended March 31, 1996 and 1997, respectively.
 
 Stock Option Plans
 
  The Company maintains the 1993 Incentive Stock Option Plan (the 1993 Plan),
the 1995 Plan and the 1996 Stock Plan (the 1996 Plan), collectively referred
to as the Plans. The 1996 Plan was approved by the Board of Directors on
December 30, 1996 and calls for shareholder approval within one year. The 1995
Plan was approved by the Board of Directors and shareholders in September
1995. In October 1995, the Company offered to exchange options issued under
the 1993 Plan for options under the 1995 Plan. With the inception of the 1996
Plan, no further options will be granted under the 1993 and 1995 Plans.
 
  Among other things, the 1996 Plan provides for granting of incentive stock
options, nonstatutory stock options, and stock appreciation rights to
employees and consultants. Unless terminated sooner, the 1996 Plan will
terminate automatically in December 2006. A total of 700,000 shares of common
stock may be issued under the 1996 Plan of which 520,700 shares are available
for grant at December 31, 1996. See Note 10 for amendment and restatement of
the 1996 Plan. Options under all plans generally vest over a four-year period,
25% after one year and the remaining portion in equal monthly increments over
the remaining three years. Options generally expire within ninety days of
termination of employment or five years after full vesting has occurred.
 
  In August 1994, the Company granted nonqualified options under individual
option agreements to purchase 106,667 shares of common stock at a per share
price of $3.75 to two of the Company's executives and majority shareholders
(53,333 options each) to settle a note payable of $400,000. This transaction
also resulted in compensation expense of $400,000 at the grant date. These
options were fully vested at the time of issuance; however, they may not be
exercised if the holder has any other unexercised options that were previously
granted to that individual. In addition, during 1994, the Company granted
other nonqualified stock options to various individuals under separate option
agreements. These options vest over periods of up to one year and expire over
periods of up to five years.
 
  In April 1995, an additional 53,333 options to purchase Class A common stock
for $30.00 per share were issued to two of the Company's executives in
connection with their employment by the Company. These options were fully
vested upon issuance and are exercisable over five years.
 
  In October 1995 and August 1996, the exercise price of options to purchase
182,375 shares and 46,673 shares of Class A common stock, respectively, were
repriced to $3.75 per share, the then fair value of the common stock, as
determined by the Company's Board of Directors.
 
  The Company issued options to purchase 179,300 shares of Class A common
stock in December 1996 and 40,267 shares of common stock in January 1997. The
Company recorded deferred compensation, for financial
 
                                     F-17
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
reporting purposes, of approximately $188,000 in 1996 and $97,000 for the
three-month period ended March 31, 1997, with respect to such option grants to
reflect the difference between the exercise price and the deemed fair value
for financial reporting purposes of these shares. Amortization of this
deferred compensation was $0 in 1996 and $18,000 in the three-month period
ended March 31, 1997. The amortization of this deferred compensation will
continue over the four year vesting period of the associated stock options.
 
  The following table summarizes stock option activity under all of the Plans:
 
<TABLE>
<CAPTION>
                                                      NUMBER OF     PRICE PER
                                                       SHARES         SHARE
                                                      ---------  ---------------
     <S>                                              <C>        <C>
     Balance at January 1, 1994......................    38,333   $3.75--$30.00
       Granted.......................................   319,722   $3.75--$33.00
       Exercised.....................................    (4,933)      $3.75
       Canceled......................................      (666)      $3.75
                                                      ---------
     Balance at December 31, 1994....................   352,456   $3.75--$33.00
       Granted.......................................   642,075   $3.75--$33.00
       Exercised.....................................      (133)      $9.00
       Canceled......................................  (187,315) $11 .25--$12.45
                                                      ---------
     Balance at December 31, 1995....................   807,083   $3.75--$33.00
       Granted.......................................   421,620       $3.75
       Exercised.....................................    (4,483)  $3.75--$9.00
       Canceled......................................   (95,218)  $3.75--$30.00
                                                      ---------
     Balance at December 31, 1996.................... 1,129,002   $3.75--$33.00
       Granted.......................................   392,014   $3.75--$15.00
       Exercised.....................................    (2,880)      $3.75
       Canceled......................................    (4,860)  $3.75--$15.00
                                                      ---------
     Balance at March 31, 1997....................... 1,513,276   $3.75--$33.00
                                                      =========
</TABLE>
 
  At March 31, 1997, vested options totaled 613,130.
 
  The following table summarizes information concerning currently outstanding
and exercisable options:
 
<TABLE>
<CAPTION>
                             OPTIONS OUTSTANDING                  OPTIONS EXERCISABLE
                --------------------------------------------- ----------------------------
                            WEIGHTED AVERAGE                    NUMBER
   EXERCISE       NUMBER       REMAINING     WEIGHTED AVERAGE EXERCISABLE WEIGHTED AVERAGE
    PRICES      OUTSTANDING CONTRACTUAL LIFE  EXERCISE PRICE  AND VESTED   EXERCISE PRICE
   --------     ----------- ---------------- ---------------- ----------- ----------------
<S>             <C>         <C>              <C>              <C>         <C>
    $3.75        1,062,707        8.42            $ 3.75        513,110        $ 3.75
    $6.00          210,414        9.76            $ 6.00            --            --
$8.25 - $33.00     240,155        8.78            $10.19        100,020        $12.87
                 ---------                                      -------
    Total        1,513,276                                      613,130
                 =========                                      =======
</TABLE>
 
 Stock-Based Compensation
 
  Pro forma information regarding results of operations and loss per share is
required by FAS 123 for awards granted after December 31, 1994 as if the
Company had accounted for its stock-based awards to employees under a
valuation method permitted by FAS 123. The value of the Company's stock-based
awards to employees in 1995 and
 
                                     F-18
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
1996 was estimated using the minimum value method. Should the Company complete
an initial public offering (IPO) of its stock, options granted after the IPO
will be valued using the Black-Scholes option pricing model. Among other
things, the Black-Scholes model considers the expected volatility of the
Company's stock price, determined in accordance with FAS 123, in arriving at
an option valuation. The minimum value method does not consider stock price
volatility. Further, certain other assumptions necessary to apply the Black-
Scholes model may differ significantly from assumptions used in calculating
the value of options granted in 1995 and 1996 under the minimum value method.
 
  The minimum value of the Company's stock-based awards to employees was
estimated assuming no expected dividends and the following weighted average
assumptions:
 
<TABLE>
<CAPTION>
                                                               1995      1996
                                                             --------- ---------
     <S>                                                     <C>       <C>
     Expected life.......................................... 8.5 years 8.5 years
     Risk-free interest rate................................      6.2%      6.3%
</TABLE>
 
  The weighted average minimum value of stock options granted during 1995 and
1996 was $0.10. Exercise prices for options outstanding as of December 31,
1996 ranged from $3.75 to $33.00. The weighted average remaining contractual
life of those options is 9.1 years. In 1996, certain options were issued at an
exercise price less than the stock price for which the weighted average
minimum value was $4.65. For pro forma purposes, the estimated minimum value
of the Company's stock-based awards to employees is amortized over the
options' vesting period. The results of applying FAS 123 to the Company's
option grants in 1995 and 1996 was not material to the results of operations
or loss per share for those years reported in the accompanying statements of
operations. Because FAS 123 is applicable only to awards granted subsequent to
December 31, 1994, its pro forma effect will not be fully reflected until
approximately 1998.
 
7. EMPLOYEE BENEFIT PLANS
 
 Retirement Savings Plan
 
  The Company maintains a contributory 401(k) plan that covers substantially
all employees. The Company contributes $0.30 for every $1.00 contributed by
the participant up to a maximum of 1.5% of the participants' compensation. The
Company contributed $5,000, $6,000, $45,000, $7,000, and $26,000 to the plan
during the years ended December 31, 1994, 1995, and 1996, and the three-month
periods ended March 31, 1996 and 1997, respectively.
 
8. INCOME TAXES
 
  As of December 31, 1996, the Company had federal and state net operating
loss carryforwards of approximately $86,000,000 and $59,000,000, respectively.
The net operating loss carryforwards will expire at various dates beginning in
the years 2003 through 2011, if not utilized.
 
                                     F-19
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
  Significant components of the Company's deferred tax assets and liabilities
for federal and state income taxes of December 31, 1995 and 1996 are as
follows:
 
<TABLE>
<CAPTION>
                                                           1995        1996
                                                        ----------  -----------
     <S>                                                <C>         <C>
     Deferred tax assets:
       Net operating loss carryforwards................ $8,500,000  $32,000,000
       Write-off of network equipment..................        --     5,000,000
       Other, net......................................    500,000    1,000,000
                                                        ----------  -----------
     Total deferred tax assets.........................  9,000,000   38,000,000
                                                        ----------  -----------
     Deferred tax liabilities:
       Other, net......................................        --     1,000,000
                                                        ----------  -----------
     Net deferred tax assets...........................  9,000,000   37,000,000
     Valuation allowance............................... (9,000,000) (37,000,000)
                                                        ----------  -----------
                                                        $      --   $       --
                                                        ==========  ===========
</TABLE>
 
  The Company believes that, based on a number of factors, the available
objective evidence creates sufficient uncertainty regarding the realizability
of the deferred tax assets such that a full valuation allowance has been
recorded. These factors include the Company's history of net losses since
inception and the fact that the market in which the Company competes is
intensely competitive and characterized by rapidly changing technology. The
Company believes that, based on the currently available evidence, it is more
likely than not that the Company will not generate taxable income through
1998, and possibly beyond, and accordingly will not realize the Company's
deferred tax assets through 1998 and possibly beyond. The Company will
continue to assess the realizability of the deferred tax assets based on
actual and forecasted operating results. In addition, the utilization of net
operating losses may be subject to a substantial annual limitation due to the
"change in ownership" provisions of the Internal Revenue Code of 1986 and
similar state provisions.
 
  The net valuation allowance increased by approximately $7,000,000 in 1995
and $28,000,000 in 1996.
 
9. OTHER MATTERS
 
  An officer of the Company is a majority shareholder of a vendor of the
Company. The Company incurred marketing fees to the vendor totaling $95,000,
$920,000, $2,450,000, $792,000, and $494,000 in the years ended December 31,
1994, 1995, 1996, and the three-month periods ended March 31, 1996 and 1997,
respectively.
 
10. SUBSEQUENT EVENTS
 
 Initial Public Offering and Direct Placements
   
  In May 1997, the Company's Board of Directors approved the filing of a Form
S-1 Registration Statement with the Securities and Exchange Commission
covering the proposed sale by the Company of up to 3,000,000 shares of its
common stock to the public plus an overallotment option for the underwriters.
On July 25, 1997, the Company's Board of Directors approved an increase in the
number of shares made available for sale to the public for up to 4,500,000
shares of its Common Stock plus an overallotment option for the underwriters.
Concurrently with the closing of this offering, certain strategic investors
have agreed to purchase directly from the Company shares of Common Stock
having an aggregate purchase price of approximately $18,000,000. All of such
shares will be unregistered shares purchased at the initial public offering
price.     
 
 
                                     F-20
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONTINUED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
  On May 1, 1997, and June 6, 1997 the Company's Board of Directors took the
following actions which were approved by the Company's shareholders on June
30, 1997:
 
    (i) Approved the reincorporation of the Company under the laws of the
  state of Delaware (effective May 1, 1997)
     
    (ii) Subject to the filing of the Amended and Restated Certificate of
  Incorporation with the Secretary of the State of Delaware (which took place
  on July 30, 1997) authorized a reverse stock split of one for 15 of the
  Company's common stock and the conversion of all previously issued and
  outstanding shares of Class B common stock into voting shares of common
  stock, amended the definition of a Qualified Public Offering that would
  trigger the automatic conversion of the shares of Series A, B, C, and D
  convertible preferred shares and authorized the issuance additional shares
  of Series B convertible preferred shares. (All capital accounts, share and
  per share data in these financial statements have been retroactively
  restated to reflect the stock split.)     
 
    (iii) Amended and restated the 1996 Stock Plan to increase the shares
  reserved for grant thereunder to 793,333.
 
    (iv) Adopted and approved the 1997 Stock Plan (the 1997 Plan) which
  provides for the granting of incentive stock options to employees and the
  granting of nonstatutory stock options and stock purchase rights to
  employees, directors, and consultants of the Company. A total of 1,500,000
  shares of the Company's common stock has been reserved for issuance
  pursuant to the 1997 Plan. Unless terminated sooner, the 1997 Plan will
  terminate automatically in 2007.
 
    (v) Adopted and approved the 1997 Employee Stock Purchase Plan (the 1997
  Purchase Plan) under which 500,000 shares of common stock have been
  reserved for issuance. The 1997 Purchase Plan allows for eligible employees
  to purchase stock at 85% of the lower of the fair market value of the
  Company's common stock as of the first day of each six-month offering
  period or at the end of the current purchase period. The Plan has 24-month
  offering periods, with each offering period divided into four consecutive
  six-month purchase periods. The initial offering period will commence on
  the first trading day on or after the closing of the initial public
  offering.
 
 Exercise of Warrants
 
  On April 18, 1997, certain preferred stockholders holding warrants to
purchase an aggregate number of 181,876 shares of Class A common stock and
66,688 shares of Series B convertible preferred stock at $11.00 per share,
exercised such warrants at a discounted price of $6.60 per share in
consideration of their early exercise. Additionally, certain preferred
stockholders exercised warrants to purchase an aggregate number of 233,660
shares of Series D convertible preferred stock at a price of $12.24,
discounted from the original price of $20.40. The Company received total
consideration of $4.5 million related to the exercise of these warrants.
 
 Unaudited Pro Forma Stockholders' Equity (Deficit)
 
  If the offering contemplated by the prospectus is consummated, all of the
convertible preferred stock outstanding as of the effective date of the
offering will automatically be converted into an aggregate of 5,692,750 shares
of common stock based on the number of shares of convertible preferred stock
outstanding at June 23, 1997. Unaudited pro forma stockholders' equity
(deficit) at March 31, 1997, as adjusted for the conversion of preferred stock
is disclosed on the balance sheet.
 
 Litigation
 
  On April 22, 1997, a complaint was filed in the Los Angeles County,
California Superior Court against the Company and other unnamed defendants by
Sattel Communications LLC (Sattel). The complaint alleges claims for
 
                                     F-21
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONCLUDED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
breach of contract, breach of the covenant of good faith and fair dealing,
unfair business practices, fraud and negligent misrepresentation. Sattel
claims that the Company is in breach of an agreement to pay for up to $4.3
million of DSS Switches from Sattel for use in the Company's network. The
Complaint also seeks unspecified consequential and punitive damages. On April
29, 1997, Sattel served the Company with an Application for Writ of
Attachment, seeking to secure a lien on the Company's assets up to an amount
of $3.6 million. At a hearing held on June 25, 1997, the Court granted the
writ. The Company has reserved approximately $5,791,000 as of March 31, 1997
for such lawsuit in case the Company is unsuccessful in its defense (see Note
3). On July 10, 1997, the Company settled the complaint with Sattel in the
amount of $4.4 million. The Company also agreed to purchase, at the election
of Sattel, up to 25% of the Company's common stock held by Sattel on the day
after the closing of the offering at the initial public offering price.
 
  In late April and early May, 1997, three putative securities class action
complaints were filed in the United States District Court, Central District by
certain stockholders of Diana Corporation (Diana), the parent corporation of
Sattel, alleging securities fraud related to plaintiffs' purchase of shares of
Diana Common Stock in reliance upon allegedly misleading statements made by
defendants, Diana, Sattel and certain of their respective affiliates, officers
and directors. Concentric was named as a defendant in the complaint in
connection with certain statements made by Diana and officers of Diana related
to Concentric's purchase of network switching equipment from Diana's Sattel
subsidiary. The complaints do not appear to allege that Concentric made any
false or misleading statements. The plaintiffs seek unspecified compensatory
damages. The Company is currently unable to estimate a range of possible
losses associated with such lawsuits.
 
  While the ultimate outcome of such litigation is uncertain, the Company
believes it has meritorious defenses to the claims and intends to conduct
vigorous defenses. An unfavorable outcome in these matters could have a
material adverse effect on the Company's financial condition. In addition,
even if the ultimate outcomes are resolved in favor of the Company, the
defense of such litigation could entail considerable cost and the diversion of
efforts of management, either or which could have a material adverse effect on
the Company's results of operations.
 
 Bridge Loans
 
  In June 1997, the Company borrowed $3 million from a third-party in the form
of a 10% convertible secured promissory note (the Secured Note) which is due
on November 30, 1997. In connection with the Secured Note, the Company will
issue a warrant to purchase shares of the Company's Common Stock (the
Warrant). The Note will automatically convert into shares of the Company's
Common Stock upon the closing of the initial public offering at a per share
conversion price equal to the initial public offering price. The Warrant,
which will expire five years from the date of grant, is exercisable for a
number of shares of Common Stock equal to 25% of the shares issuable upon
conversion of the Note at a per share exercise price of 50% of the initial
public offering price.
 
  In June 1997, the Company borrowed $2 million from a stockholder in the form
of a 10% unsecured promissory note (the Unsecured Note). The Unsecured Note is
due no later than five days following the initial public offering. In
connection with the Unsecured Note, the Company will issue a warrant, which
will expire five years from the date of grant, to purchase shares of the
Company's Common Stock (the Warrant). The Warrant is exercisable for a number
of shares of Common Stock determined by multiplying the principal amount of
the loan by 50% and dividing that sum by the initial public offering price per
share. The exercise price will be equal to 50% of the initial public offering
price.
 
 
  The Company deemed the fair value of the above warrants, using the Black-
Scholes method, to be approximately $930,000, which will be recorded as a
discount to the above promissory notes. Such discount will be amortized to
interest expense over the estimated term of the notes.
 
                                     F-22
<PAGE>
 
                        CONCENTRIC NETWORK CORPORATION
 
                  NOTES TO FINANCIAL STATEMENTS--(CONCLUDED)
 
(INFORMATION AT MARCH 31, 1997 AND FOR THE THREE-MONTH PERIODS ENDED MARCH 31,
                          1996 AND 1997 IS UNAUDITED)
 
 
  In June 1997, the Company entered into a software license agreement with a
third-party. The Company used the $2 million proceeds from the Unsecured Note
as a down payment to the third-party and is obligated to pay $3 million by
July 31, 1997.
 
COMMITMENT
 
  In July 1997, the Company entered into a five-year service and equipment
agreement under which a third-party will provide telecommunication services
and equipment. The agreement provides for minimum payments as follows: $1.2
million in 1998, $2.5 million in 1999, $7.0 million in 2000, $6.5 million in
2001 and $4.0 million in 2002. At the election of the third party, $2.0
million of the minimum payments may be paid by the issuance of common stock of
the Company at the then-current fair market value.
 
                                     F-23
<PAGE>
 
                  VALUE-ADDED CONCENTRIC NETWORKING SOLUTIONS

                  [PICTURE OF STACKS OF CUBES APPEARS HERE]


                       [PICTURE OF CUBE APPEARS HERE]

                                      VPN

 Concentric Network specializes in building, operating and supporting virtual 
 private networks (VPNs) for an enterprise's customers, business partners and 
                                  employees.

                       [PICTURE OF CUBE APPEARS HERE]

                               DEDICATED ACCESS
 
Concentric Network offers dedicated access facilities targeted at businesses 
    that desire single or multipoint high-speed, dial-up and/or dedicated 
                     connections to distributed locations.

                       [PICTURE OF CUBE APPEARS HERE]

                                REMOTELINK(TM)

 Concentric RemoteLink flexibly and cost-effectively allows mobile or remote 
   employees to securely access their corporate LAN with a low cost dial-up 
                                  connection.

                       [PICTURE OF CUBE APPEARS HERE]

                              CONCENTRICHOST(TM)

Concentric Network hosting services offer a variety of options for consumers and
enterprises to cost-effectively tailor their Internet and Intranet presence to 
             their needs, with power, speed, ease and flexibility.

                       [PICTURE OF CUBE APPEARS HERE]

                               GAME GATEWAY(TM)

Concentric's Game Gateway affords consumers a one-stop source to a number of the
  major online game networks with the convenience of a single billing account.

                       [PICTURE OF CUBE APPEARS HERE]

                               CUSTOMER SUPPORT

   Concentric Network's highly-trained customer support representatives are 
equipped with comprehensive diagnostic tools to provide expertise and back-up 
service via the Web or directly via telephone 24 hours a day, seven days a week.

                       [PICTURE OF CUBE APPEARS HERE]

                           HIGH-PERFORMANCE NETWORK

The Concentric network provides low fixed latency and high throughput for a wide
 range of value-added services. Security, speed and flexibility are a central 
                                    focus.


           [A PICTURE OF A GLOBE INSIDE CONCENTRIC CIRCLES AS THE 
              CONCENTRIC NETWORK CORPORATION LOGO APPEARS HERE]

          [CONCENTRIC NETWORK CORPORATION APPEARS ALONG RIGHT MARGIN]
<PAGE>
 
- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
 
  No dealer, salesperson or other person has been authorized to give any in-
formation or to make any representation not contained in this Prospectus and,
if given or made, such information or representations must not be relied upon
as having been authorized by the Company or any Underwriter. This Prospectus
does not constitute an offer to sell or the solicitation of any offer to buy
any of the securities offered hereby in any jurisdiction to any person to whom
it is unlawful to make such offer in such jurisdiction. Neither the delivery
of this Prospectus nor any sale made hereunder shall, under any circumstances,
create any implication that the information herein is correct as of any time
subsequent to the date hereof or that there has been no change in the affairs
of the Company since such date.
 
                                ---------------
 
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                                          PAGE
                                                                          ----
<S>                                                                       <C>
Prospectus Summary.......................................................   3
Risk Factors.............................................................   7
Use of Proceeds..........................................................  22
Dividend Policy..........................................................  22
Direct Placements........................................................  22
Capitalization...........................................................  23
Dilution.................................................................  24
Selected Financial Data..................................................  25
Management's Discussion and Analysis of Financial Condition and Results
 of Operations...........................................................  26
Business.................................................................  33
Management...............................................................  49
Certain Transactions.....................................................  59
Principal Stockholders...................................................  64
Description of Capital Stock.............................................  66
Rescission Offers........................................................  69
Shares Eligible for Future Sale..........................................  69
Underwriting.............................................................  72
Legal Matters............................................................  73
Experts..................................................................  73
Additional Information...................................................  74
Glossary................................................................. G-1
Index to Financial Statements............................................ F-1
</TABLE>
 
                                ---------------
 
  Until       1997 (25 days after the date of this Prospectus), all dealers
effecting transactions in the registered securities, whether or not
participating in this distribution, may be required to deliver a Prospectus.
This is in addition to the obligation of dealers to deliver a Prospectus when
acting as Underwriters and with respect to their unsold allotments or
subscriptions.
 
- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
 
                               3,000,000 SHARES

                   [LOGO OF CONCENTRIC NETWORK CORPORATION]
                                 COMMON STOCK
 
                                ---------------
                                  PROSPECTUS
                                       , 1997
                                ---------------
 
                                UBS SECURITIES
 
                               UNTERBERG HARRIS
 
                          WHEAT FIRST BUTCHER SINGER
 
- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------
<PAGE>
 
                                    PART II
 
                    INFORMATION NOT REQUIRED IN PROSPECTUS
 
ITEM 13. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION
 
  The following table sets forth all expenses, other than underwriting
discounts and commissions, payable by the Company in connection with the sale
of the Common Shares being registered. All of the amounts shown are estimates
except for the SEC registration fee and the NASD filing fee.
 
<TABLE>   
   <S>                                                               <C>
   SEC Registration Fee............................................. $   15,055
   NASD Filing Fee..................................................      5,468
   Nasdaq National Market Listing Fee...............................     40,000
   Blue Sky Qualification Fees and Expenses.........................     10,000
   Printing and Engraving Expenses..................................    100,000
   Legal Fees and Expenses..........................................    500,000
   Accounting Fees and Expenses.....................................    250,000
   Transfer Agent and Registrar Fees................................     10,000
   Miscellaneous....................................................     69,477
                                                                     ----------
     Total.......................................................... $1,000,000
                                                                     ==========
</TABLE>    
 
ITEM 14. INDEMNIFICATION OF DIRECTORS AND OFFICERS
 
  In May 1997, the Registrant entered into indemnification agreements with its
directors and officers providing for limitations on a director's and officer's
liability for judgments, settlements, penalties, fines and expenses of defense
(including attorneys' fees, bonds and costs of investigation) arising out of
or in any way related to acts or omissions as a director or an officer, or in
any other capacity in which services are rendered to the Registrant. The
Registrant believes its indemnification agreements will assist it in
attracting and retaining qualified individuals to serve as directors and
officers. The agreements provide that a director or officer is not entitled to
indemnification under such agreements (i) if the director or officer is not
relieved of liability under applicable law, (ii) for violations of certain
securities laws, or (iii) for certain claims initiated by the officer or
director. Due to the lack of applicable case law, it is not clear whether
indemnification is available in case of a breach of securities laws of the
U.S.
 
  As permitted by Section 145 of the Delaware General Corporation Law, the
Registrant's Amended and Restated Certificate of Incorporation to be effective
upon completion of the offering include a provision that eliminates the
personal liability of its directors for monetary damages for breach or alleged
breach of their duty of care. In addition, as permitted by Section 145 of the
Delaware General Corporation Law, the Bylaws, as amended, of the Registrant to
be effective upon completion of the offering provide that: (i) the Registrant
is required to indemnify its directors and officers and persons serving in
such capacities in other business enterprises (including, for example,
subsidiaries of the Registrant) at the Registrant's request, to the fullest
extent permitted by Delaware law, including in those circumstances in which
indemnification would otherwise be discretionary; (ii) the Registrant may, in
its discretion, indemnify employees and agents in those circumstances where
indemnification is not required by law; (iii) the Registrant is required to
advance expenses, as incurred, to its directors and officers in connection
with defending a proceeding (except that it is not required to advance
expenses to a person against whom the Registrant brings a claim for breach of
the duty of loyalty, failure to act in good faith, intentional misconduct,
knowing violation of law or deriving an improper personal benefit); (iv) the
rights conferred in the Bylaws, as amended, are not exclusive, and the
Registrant is authorized to enter into indemnification agreements with its
directors, officers and employees; and (v) the Registrant may not
retroactively amend the Bylaw provisions in a way that is adverse to such
directors, officers and employees.
 
  The Registrant's policy is to enter into indemnification agreements with
each of its directors and officers that provide the maximum indemnity allowed
to directors and officers by Section 45 of the Delaware General Corporation
Law and the Bylaws, as amended, as well as certain additional procedural
protections.
 
                                     II-1
<PAGE>
 
  The indemnification provisions in the Bylaws, as amended, and the
indemnification agreements entered into between the Registrant and its
directors and officers may be sufficiently broad to permit indemnification of
the Registrant's directors and officers for liabilities arising under the
Securities Act.
 
ITEM 15. RECENT SALES OF UNREGISTERED SECURITIES
 
  During the three years preceding the date hereof, the Company has made the
following sales of securities that were not registered under the Securities
Act (share numbers are approximate and actual numbers of shares may differ as
a result of rounding calculations related to the one-for-15 reverse split and
do not reflect, in the case of Preferred Stock and warrants exercisable
therefor, the conversion of Preferred Stock into Common Stock that will occur
automatically immediately prior to the closing of the offering):
 
    1. From June 1993 to March 1995, the Company sold to various investors
  convertible debentures and convertible subordinated debentures
  (collectively, the "Convertible Debentures") in the aggregate principal
  amount of $4,260,000. As of March 31, 1997, all of the Convertible
  Debentures had been converted into shares of Class A Common Stock at prices
  ranging from $3.75 per share to $11.25 per share.
 
    2. From June 1993 to March 1995, the Company sold to various investors
  29,673 shares of Class A Common Stock at $30.00 per share, for an aggregate
  consideration of $890,200.
 
    3. Since June 1993 the Company has issued 24,611 shares of Class A Common
  Stock, at prices from $11.25 to $30.00, to individuals or other entities on
  account of services rendered by them to the Company.
 
    4. In October 1994, the Company issued 30,917 shares of Class A Common
  Stock to Linkon Corporation ("Linkon") in exchange for 66,170 shares of the
  Company's Common Stock held by Linkon and Linkon's forgiveness of the
  Company's debt to Linkon.
 
    5. In connection with the 1994 master lease agreement with Racal, the
  Company granted to Racal warrants to purchase 44,935 shares of the
  Company's Class A Common Stock exercisable through September 1, 1998 at
  $15.00 per share subject to adjustment. As a result of the options granted
  to certain members of management in October 1995, the exercise price of the
  warrants was decreased to $3.75 per share.
 
    6. In February 1995, the Company granted to Racal warrants to purchase
  5,000 shares of the Company's Class A Common Stock in consideration for
  securing the Company's loan from Sun Bank South Florida, National
  Association (the "Sun Bank Loan"). The Company has since repaid the Sun
  Bank Loan. Racal may exercise the warrants through February 15, 2000, at a
  price equal to the lowest of (i) $30.00 per share, (ii) the lowest price
  per share at which the Company may sell shares of Common Stock (or
  securities convertible into or exchangeable for shares of its Common
  Stock), and (iii) the lowest price at which the holder of the warrant,
  option or other Company security entitling the holder to purchase shares of
  the Company's Common Stock may purchase such shares on or after February
  15, 1995.
 
    7. In connection with the 1995 master lease agreement between the Company
  and Comdisco, Inc., the Company has issued to Comdisco a warrant to
  purchase up to 17,453 shares of Class A Common Stock for a purchase price
  of $10.82 subject to adjustment.
 
    8. On April 20, 1995, the Company sold to GS Capital Partners L.P.
  ("GSCP"), Kleiner Perkins Caufield & Byers VII ("KPCB"), and KPCB VII
  Founders Fund (together with KPCB, "KP") an aggregate of 906,453 shares of
  the Company's Series A Preferred Stock ("Series A Preferred Shares") and
  warrants to purchase an aggregate of 181,876 Class A Common Stock for an
  aggregate consideration of approximately $10,000,000 pursuant to a
  preferred stock and warrant purchase agreement (the "Series A Agreement").
  The warrants issued pursuant to the Series A Agreement had an initial
  exercise price of $11.00 for each share of Class A Common Stock. On April
  18, 1997, the Investors exercised the warrants at a discounted price of
  $6.60 per share. See "Certain Transactions" and "Description of Capital
  Stock."
 
    9. The Series A Agreement provided that in the event that the book value
  of the shares of the Company decreased an amount in excess of $100,000 as a
  result of certain events, including the breach of any representation or
  warranty in the Series A Agreement, GSCP and KP would be entitled to
  receive indemnification, in the form of additional shares of Class A Common
  Stock. In consideration of GSCP's and
 
                                     II-2
<PAGE>
 
  KP's waiver of their right to be indemnified in the future the Company
  agreed, in October 1995, to issue to GSCP and KP an aggregate of 61,678
  shares of Class A Common Stock.
 
    10. In connection with the alliance between Intuit and the Company, on
  December 11, 1995, Intuit received warrants to purchase $1.5 million worth
  of Series B Preferred Stock at an initial exercise price of $11.00 per
  share and warrants to purchase $3.5 million worth of Series B Preferred
  Stock at the closing sale price of the Company's next preferred stock sale,
  which was $27.30 per share. Also in connection with the arrangements with
  Intuit, GSCP and the Kleiner Entities made bridge loans totaling $2 million
  to the Company on October 16, 1995, which were rolled over into bridge
  loans totaling $4 million on November 6, 1995. On November 29, 1995, GSCP
  made a further bridge loan of $3 million. In consideration of these loans,
  GSCP and the Kleiner Entities received warrants to purchase shares of
  Series B Preferred Stock at an exercise price of $11.00 per share.
  Effective as of December 20, 1995, GSCP and the Kleiner Entities converted
  the principal and interest due under their $2 million promissory notes into
  a total of 366,947 shares of Series B Preferred Stock at a price of $11.00
  per share. Also effective as of February 1996, GSCP converted the entire
  amount of principal and interest on its $3 million bridge note into 123,297
  Series C Shares at an exercise price of $24.57 per share.
 
    11. On December 20, 1995, the Company issued a total of 804,945 shares of
  Series C Preferred Stock ("Series C Shares") at a price of $27.30 per
  share. An additional 123,297 Series C Shares were issued to GSCP at $24.57
  per share when it converted its $3 million bridge loan in January 1996.
 
    12. On June 6, 1996, the Company closed a Bridge Loan from Sattel
  Communications, LLC ("Sattel") for $5,000,000 evidenced by a convertible
  Promissory Note dated June 6, 1996. The Company issued Sattel a warrant
  dated June 6, 1996, to purchase 36,765 shares of the Company's Series D
  Preferred Stock at an exercise price of $20.40 per share. On August 21,
  1996, Sattel converted the bridge loan into shares of Series D Preferred
  Stock at $20.40 per share.
 
    13. On July 31, 1996, the Company closed a Bridge Loan from Matthew Bross
  for $50,000 evidenced by a convertible Promissory Note dated July 29, 1996.
  The Company issued Matthew Bross a warrant dated July 31, 1996, to purchase
  2,451 shares of Series D Preferred Stock at an exercise price of $20.40 per
  share. On August 21, 1996, the Company repaid the loan.
 
    14. On July 31, 1996, the Company closed a Bridge Loan from Maritime
  Capital Partners, L.P. for $500,000, evidenced by a convertible Promissory
  Note dated July 29, 1996. The Company issued Maritime a warrant dated July
  31, 1996, to purchase 24,510 shares of Series D Preferred Stock at an
  exercise price of $20.40 per share. On August 21, 1996, the Company repaid
  the loan.
 
    15. On July 31, 1996, the Company closed a Bridge Loan from GSCP for
  $300,000, evidenced by a convertible Promissory Note dated July 29, 1996.
  The Company issued GSCP a warrant dated July 31, 1996, to purchase 14,706
  shares of Series D Preferred Stock at an exercise price of $20.40 per
  share. The Company repaid the loan on August 21, 1996.
 
    16. On July 31, 1996, the Company closed a Bridge Loan from KPCB for
  $300,000 evidenced by a convertible Promissory Note dated July 29, 1996.
  The Company issued to KPCB a warrant dated July 31, 1996, to purchase
  14,706 shares of Series D Preferred Stock at an exercise price of $20.40
  per share. The Company repaid the loan on August 21, 1996.
 
    17. On July 31, 1996, the Company closed a Bridge Loan from Henry
  Nothhaft for $100,000 evidenced by a Promissory Note dated July 29, 1996.
  The Company issued Henry Nothhaft a warrant dated July 31, 1996, to
  purchase 4,902 shares of Series D Preferred Stock at an exercise price of
  $20.40 per share. The Company repaid the loan on August 21, 1996.
 
    18. On July 31, 1996, the Company closed a Bridge Loan from John Peters
  for $50,000 evidenced by a Promissory Note dated July 29, 1996. The Company
  issued John Peters a warrant dated July 31, 1996, to purchase 2,451 shares
  of Series D Preferred Stock at an exercise price of $20.40 per share. The
  Company repaid the loan on August 21, 1996.
 
    19. On August 16, 1996, the Board of Directors amended the vesting
  provisions of options to purchase 14,000 shares issued to Henry Nothhaft,
  President, Chief Executive Officer and a director of the Company, on
 
                                     II-3
<PAGE>
 
  October 31, 1995, and an option to purchase 11,900 shares issued to John
  Peters, Executive Vice President and General Manager, Network Services
  Division, on October 31, 1995, so the options would fully vest as of the
  closing date of the sale of at least $29,000,000 of Series D Preferred
  Stock of the Company, which occurred on August 21, 1996.
 
    20. On August 21, 1996, the Company exchanged four options previously
  issued to Randy Maslow, a director of the Company, for new options
  exercisable for an aggregate of 46,673 shares of Class A Common Stock at
  $3.75 per share. The four-year vesting schedule accelerates so that all
  shares vest immediately in the event of an initial public offering or a
  change of control. The options may be exercised through their expiration
  date regardless of when Mr. Maslow ceases being an employee or consultant.
  Mr. Maslow's employment with the Company ended on October 31, 1996.
 
    21. On August 21, 1996, the Company sold 1,670,176 shares of Series D
  Preferred Stock at $20.40 per share for an aggregate price of $34,000,000.
 
    22. Between October 25, 1996 and November 5, 1996, the Company sold an
  additional 1,029,412 shares of Series D Preferred Stock at $20.40 per share
  for an aggregate price of $21,000,000.
 
    23. In December 1995, the Company issued options for the purchase of
  60,000 shares of Class A Common Stock to employees of Critical Technologies
  Incorporated ("CTI"), a company that provides network operations services
  to the Company. The options were issued pursuant to the Company's Employee
  Staffing and Services Agreement with CTI, dated November 1, 1995. In
  October 1996, the Board ratified an amendment to the Company's agreement
  with CTI to provides that performance conditions applicable to 13,334 of
  the 60,000 optioned shares will be deemed satisfied.
 
    24. On March 5, 1997, in consideration of distribution agreements with
  the Company, TMI Telemedia International, Ltd. was issued a warrant for
  176,678 shares of Series D Preferred Stock at an exercise price of $20.40
  per share.
 
    25. On April 4, 1997, the Company entered into warrant amendment
  agreements with TMI, GSCP, and the Kleiner Entities to reduce the exercise
  price of certain of their warrants in return for the immediate exercise of
  such warrants. The exercise price of warrants for 181,876 shares of Class A
  Common Stock and 66,888 shares of Series B Preferred Stock held by GSCP and
  the Kleiner Entities was reduced from $11.00 to $6.60 per share. The
  exercise price of warrants for 233,660 shares of Series D Preferred Stock
  held by GSCP, KPCB and TMI was reduced from $20.40 per share to $12.24 per
  share. Also, in connection with the reduction of the exercise price of the
  GSCP and Kleiner Entities' Common Stock warrants, the exercise price of
  Intuit's $1.5 million warrant was similarly reduced to $0.44 per share, and
  the expiration date was extended to December 31, 2000.
 
    26. In May 1997, the Company issued an aggregate of 106,754 shares of
  Series A Preferred Stock to two shareholders of the Company in exchange for
  106,754 shares of Class B Common Stock then held by them.
 
    27. Between March 31, 1996, and May 18, 1997, nonplan options to purchase
  a total of 3,418 shares of Common Stock were exercised by three optionees
  at prices ranging from $3.75 to $9.00 per share.
 
    28. 1993 Incentive Stock Option Plan. The Company's 1993 Incentive Stock
  Option Plan (the "1993 Plan") provides for the grant to employees of the
  Company of incentive stock options. As of June 25, 1997, options to
  purchase 5,067 shares of Common Stock had been exercised at an exercise
  price of $3.75 per share under the 1993 Plan by three optionees, and
  options to purchase 53,346 shares of Class A Common Stock at a weighted
  average exercise price of $12.38 per share were outstanding. No future
  grants will be made under the 1993 Plan. The exercise price of all stock
  options granted under the 1993 Plan must be at least equal to the fair
  market value of the Common Stock on the date of grant. With respect to any
  participant who owns stock possessing more than 10% of the voting power of
  all classes of stock of the Company, the exercise price of any stock option
  granted to such person must be at least 110% of the fair market value on
  the grant date, and the maximum term of such option is five years. The term
  of all other options granted under the 1993 Plan may be up to 10 years.
  Options granted under the 1993 Option Plan must be exercised before the
  optionee terminates his or her status as an employee of the Company, or
  within three months after such optionee's termination by disability, or
  within 12 months after termination by death. In October 1995, the Board
  approved an exchange offer pursuant to which all employees would exchange
  their options for options granted under the 1995 Stock Incentive Plan for
  Employees and Consultants (the "1995 Plan").
 
 
                                     II-4
<PAGE>
 
    29. 1995 Stock Incentive Plan for Employees and Consultants. The
  Company's 1995 Plan provides for the granting to employees of incentive
  stock options within the meaning of Section 422 of the Internal Revenue
  Code of 1986, as amended (the "Code"), and for the granting to employees
  and consultants of nonstatutory stock options, stock appreciation rights
  ("SARs") and restricted stock awards ("RSAs"). No SARs or RSAs have been
  granted under the 1995 Plan. The 1995 Plan was approved by the Board of
  Directors and Stockholders in September 1995, and an amendment decreasing
  the number of shares thereunder from 840,000 to 762,600 was approved by the
  Board of Directors in February 1996. The 1995 Plan was terminated effective
  October 4, 1996, and no further grants are being made thereunder except to
  the extent that an exchange of options under the Company's 1993 Plan for
  options under the 1995 Plan, which exchange was begun in October 1995, is
  continuing and has not yet been completed. A total of 762,600 shares of
  Common Stock are reserved for issuance pursuant to the 1995 Plan. As of
  June 30, 1997, options to purchase 346,500 shares of Common Stock at a
  weighted exercise price of $3.75 per share were outstanding. Nine optionees
  have exercised 6,151 shares of Common Stock under the 1995 Plan at an
  exercise price of $3.75 per share.
 
    The 1995 Plan may be administered by the Board of Directors or a
  committee of the Board of Directors, which committee is required, once the
  Company's Common Stock becomes publicly traded, to be constituted to comply
  with Rule 16b-3 promulgated under the Securities Exchange Act of 1934, as
  amended, and applicable laws. The administrator has the power to determine
  the terms of the options granted, including the exercise price, the number
  of shares subject to the option and the exercisability thereof, and the
  form of consideration payable upon exercise. Options granted under the 1995
  Plan are not generally transferable by the optionee, and each option is
  exercisable during the lifetime of the optionee only by such optionee.
  Options granted under the 1995 Plan must be exercised within three months
  of the end of such optionee's status as an employee or consultant of the
  Company, or within 12 months after such optionee's termination by death or
  disability, but in no event later than the expiration of the option's term,
  which may not exceed ten years. The exercise price of all options granted
  under the 1995 Plan must be at least equal to the fair market value of the
  Common Stock on the date of grant. With respect to any participant who owns
  stock possessing more than 10% of the voting power of all classes of the
  Company's outstanding capital stock, the exercise price of any option must
  equal at least 110% of the fair market value on the grant date and the term
  of the option must not exceed five years. The term of all other options
  granted under the 1995 Plan may not exceed 10 years.
 
    The 1995 Plan provides that in the event of a recapitalization, stock
  split, stock dividend, combination or reclassification or other increase or
  decrease in the number of issued shares of Common Stock without
  consideration, the Committee shall adjust the number of shares subject to
  each outstanding stock option, as well as the exercise price. In the event
  of dissolution or liquidation of the Company, unexercised stock options
  will terminate immediately prior to such event, after advance notice to
  participants. In the event of a merger or the sale of substantially all
  assets of the Company, each option shall be assumed or substituted. Options
  not assumed or substituted shall terminate on the date of closing of the
  merger.
     
    30. Amended and Restated 1996 Stock Plan. The Company's Amended and
  Restated 1996 Stock Plan (the "Restated 1996 Plan") provides for the
  granting to employees of incentive stock options within the meaning of
  Section 422 of the Code, and for the granting to employees, directors and
  consultants of nonstatutory stock options and stock purchase rights
  ("Rights"). The 1996 Plan was initially approved by the Board of Directors
  effective as of December 1996. It was amended and restated in May 1997 and
  approved by the Stockholders at the 1997 annual meeting. Unless terminated
  sooner, the Restated 1996 Plan will terminate automatically in December
  2006. A total of 1,100,000 shares of Common Stock are currently reserved
  for issuance pursuant to the Restated 1996 Plan. As of June 30, 1997,
  options to purchase 844,513 shares of Class A Common Stock at a weighted
  average exercise price of $6.45 per share were outstanding, and shares of
  Class A Common Stock remained available for future grant under the Restated
  1996 Stock Plan.     
 
    The Restated 1996 Plan may be administered by a committee of the Board of
  Directors constituted to comply with applicable laws (the "Committee") or
  by the Board itself. The Board or Committee (the "Administrator") has the
  power to determine the terms of the options or Rights granted, including
  the exercise price, the number of shares subject to each option or Right,
  the exercisability thereof, or any vesting acceleration or waiver of
  forfeiture conditions. The Administrator may determine the form of payment
  upon exercise, including cash, check, promissory note, other shares,
  cashless exercise or a combination of the foregoing. The Board has the
  authority to amend, suspend or terminate the Restated 1996 Plan, provided
  that no such action may impair the rights of any optionee or Right holder
  without that person's consent.
 
                                     II-5
<PAGE>
 
    Options and Rights granted under the Restated 1996 Plan are not generally
  transferable by the optionee or Right holder other than by will or the laws
  of descent and distribution, and each option and Right is exercisable
  during the lifetime of the optionee or Right holder only by such optionee
  or Right holder. The form of option agreement currently in use provides
  that options generally must be exercised within 90 days of the end of
  optionee's status as an employee, director or consultant of the Company.
  Under the Plan, options must be exercised within twelve months after such
  optionee's termination by death or disability, but in no event later than
  the expiration of the option's term. In the case of Rights, unless the
  Administrator determines otherwise, the Restricted Stock Purchase Agreement
  shall grant the Company a repurchase option exercisable upon the voluntary
  or involuntary termination of the purchaser's service with the Company for
  any reason (including death or disability). The purchase price for shares
  repurchased pursuant to the Restricted Stock Purchase Agreement shall be
  the original price paid by the purchaser and may be paid by cancellation of
  any indebtedness of the purchaser to the Company. The repurchase option
  shall lapse at a rate determined by the Administrator but in no case more
  slowly than 20% per year over five years. Generally, options vest 25% after
  one year and 1/36 per month thereafter. The exercise price of all incentive
  stock options granted under the Restated 1996 Plan must be at least equal
  to the fair market value of the Common Stock on the date of grant. The
  exercise price of nonstatutory stock options and Rights must at least be
  equal to 85% of the fair market value of the Common Stock on the date of
  grant. With respect to any participant who owns stock possessing more than
  10% of the voting power of all classes of the Company's outstanding capital
  stock, the exercise price of any incentive or nonstatutory stock option
  granted must equal at least 110% of the fair market value on the grant
  date. The term of an incentive stock option granted to such a 10%
  Stockholder must not exceed five years. The term of other options granted
  under the Restated 1996 Plan may not exceed ten years.
 
    The Restated 1996 Plan provides that in the event of a merger of the
  Company with or into another corporation, a sale of substantially all of
  the Company's assets or a like transaction involving the Company, each
  option shall be assumed or an equivalent option substituted by the
  successor corporation. If the outstanding options are not assumed or
  substituted as described in the preceding sentence, the Administrator shall
  provide for the optionee or Right holder to have the right to exercise the
  option or Right as to all of the optioned stock, including shares as to
  which it would not otherwise be exercisable. If the Administrator makes an
  option or Right exercisable in full in the event of a merger or sale of
  assets, the Administrator shall notify the optionee or Right holder that
  the option or Right shall be fully exercisable for a period of fifteen days
  from the date of such notice, and the option or Right will terminate upon
  the expiration of such period. The forms of option agreement and restricted
  stock purchase agreement currently in use provide for a 180-day lockup of
  the optionee's or Right holder's shares in the event of the Company's
  initial public offering. The option exercise notice and the restricted
  stock purchase agreement also grant the Company a right of first refusal
  (prior to the initial public offering) on the sale or transfer of any
  shares purchased pursuant to an option or Right, other than transfers by
  gift, operation of law or certain family transfers.
 
  31. On June 19, 1997, the Company closed a Bridge Loan from Williams
Communications Group, Inc. ("WCG") for $3,000,000 evidenced by a Promissory
Note which will automatically convert into shares of Common Stock upon the
closing of this offering at a conversion price equal to the initial Price to
Public made in the offering hereby. In connection with this Bridge Loan, the
Company issued WCG a warrant to purchase shares of Common Stock equal to 25%
of the number of shares of Common Stock issuable upon conversion of the
Promissory Note. Such warrant is exercisable after the close of this offering
at an exercise price per share equal to 50% of the Price to Public and expires
on June 19, 2002.
 
  32. On June 27, 1997, the Company closed a bridge loan with Kleiner Perkins
Caufield & Byers VII and KPCB Information Sciences Zaibatsu Fund VII for
$1,950,000 and $50,000, respectively, evidenced by promissory notes dated June
27, 1997. The Company issued each of the noteholders a warrant exercisable for
that number of shares of Common Stock equal to 50% of the principal amount of
the respective note divided by the Price to Public. The exercise price per
share for each of the warrants is 50% of the Price to Public.
 
 
                                     II-6
<PAGE>
 
  The sales and issuances of securities in the transactions described in
paragraphs 4-27 and 31-32 above were deemed to be exempt from registration
under the Act in reliance upon (i) Section 4(2) of the Securities Act and
Regulation D promulgated thereunder as transactions by an issuer not involving
any public offering, or (ii) Rule 701 promulgated thereunder as transactions
pursuant to a compensatory benefit plan or a written contract relating to
compensation.
 
  The issuances described in paragraphs 1, 2 and 3 were not made pursuant to a
registration statement under the Act, nor were the offer and sale registered or
qualified under any state securities laws. Although the Company believed at the
time that such offers, sales and conversion were exempt from such registration
or qualification, they may not have been exempt. As a result, purchasers of
such securities may have the right under the Act or such state securities laws,
to rescind their purchases, and thereby be entitled to return such securities
to the Company and receive back from the Company the full consideration paid by
such purchasers plus interest. No claims for any such rescission have been
asserted against the Company. The effective price per share of Common Stock of
such purchases ranged from $3.75 to $30.00. The Company expects to initiate a
rescission offer to all such holders simultaneous with this offering. If all
such holders accept such rescission offer, the Company would be required to
apply up to $1,700,000 of the proceeds of this placement towards such
rescission. The repurchase of shares pursuant to the rescission offer may give
rise to an obligation of the Company to issue additional shares of Common Stock
to certain holders of Series A Preferred Stock.
 
  In addition, options issued pursuant to the Company's 1995 Stock Incentive
Plan for Employees and Consultants (the "1995 Plan") and nonplan options for
the purchase of Common Stock were issued to approximately 150 to 200 people in
California in 1995 and 1996 for which the Company was unable to rely on the
exemption provided by Section 25102(f) of the California Corporations Code. In
March 1996, the Company was denied a permit for these issuances by the
California Commissioner of Corporations as a result of the Company's two
classes of Common Stock with differing voting rights. In addition, a smaller
number of options were issued to optionees in other states, including Michigan,
Missouri, Virginia, Washington and Florida, for which the Company may not have
had available an exemption from qualification. Also, the November 17, 1995,
grant of options for the purchase of 60,000 shares of Common Stock to employees
of Critical Technologies Incorporated was not qualified and may not have had an
exemption available under the blue sky laws of California. The aforementioned
options are potentially subject to rescission, and the Company intends to
include them in its planned Rescission Offer discussed above. Under such
Rescission Offer, the Company could be required to make an aggregate payment of
up to approximately $940,000. As of the date hereof, management is not aware of
any claims for rescission against the Company. While the Company will offer to
rescind the securities sales, there are no assurances that the Company will not
otherwise be subject to possible penalties or fines relating to these
issuances. The Company believes the Rescission Offers could provide it with
additional meritorious defenses to any such future claims. See "Risk Factors--
Rescission Offers," "Use of Proceeds," "Rescission Offers," "Shares Eligible
for Future Sale" and Note 5 to the Financial Statements.
 
ITEM 16. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES
 
  (a) Exhibits
 
<TABLE>   
 <C>    <S>
  1.1** Form of Underwriting Agreement.

  2.1** Merger Agreement.

  3.1** Form of Amended and Restated Certificate of Incorporation of Registrant
         prior to completion of this offering.

  3.2** Form of Amended and Restated Certificate of Incorporation of Registrant
         to be effective upon completion of this offering.

  3.3** Amended and Restated Bylaws of Registrant prior to completion of this
         offering.

  3.4** Amended and Restated Bylaws of Registrant to be effective upon
         completion of this offering.

  4.1** Form of Registrant's Common Stock Certificate.

  5.1** Opinion of Wilson Sonsini Goodrich & Rosati, Professional Corporation,
         regarding legality of the securities being issued.
</TABLE>    
 
 
                                      II-7
<PAGE>
 
<TABLE>   
 <C>      <S>
 10.1**   Amended and Restated Registration Rights Agreement, as amended and
           restated as of August 21, 1996, by and among the Registrant, GS
           Capital Partners, L.P., Kleiner Perkins Caufield & Byers VII,
           Comdisco, Inc., Intuit, Inc., certain listed holders of Series C
           Convertible Preferred Stock, certain listed holders of Common Stock,
           certain listed holders of Series D Convertible Preferred Stock, and
           Racal-Datacom, Inc.
 10.2**   Preferred Stock and Warrant Purchase Agreement, dated as of April 20,
           1995, by and among the Registrant, GS Capital Partners, L.P., and
           Kleiner Perkins Caufield & Byers VII and KPCB Information Sciences
           Zaibatsu Fund II, as amended.
 10.3**   Form of Director and Officer Indemnification Agreement.
 10.4**   1995 Stock Incentive Plan for Employees and Consultants, as amended
           February 21, 1996.
 10.5**   Amended and Restated 1996 Stock Plan.
 10.6**   1997 Stock Plan.
 10.7**   1997 Employee Stock Purchase Plan.
 10.8**   Termination of Services and Indemnification Agreement, dated as of
           February 15, 1996, by and between the Registrant and Marc Collins-
           Rector and Chad Shackley.
 10.9**   Agreement, dated as of February 15, 1996, by and between the
           Registrant and Randy Maslow.
 10.10**  Governance Agreement, dated May 15, 1997, by and among the
           Registrant, Marc Collins-Rector, Chad Shackley, GS Capital Partners,
           L.P., Kleiner Perkins Caufield & Byers VII, KPCB VII Founders Fund,
           KPCB Information Sciences Zaibatsu Fund II, and Intuit, Inc.
 10.11+** Employee Services and Staffing Agreement, dated November 1, 1995,
           between the Registrant and Critical Technologies, Inc., as amended
           on September 30, 1996, and October 23, 1996, including Colocation
           Services Agreement, dated as of November 1, 1994, between the
           Registrant and Critical Technologies, Inc. and amendments thereto.
 10.12+** Internet-Sign Up Wizard Referral and Microsoft Internet Explorer
           License and Distribution Agreement, dated March 28, 1997, between
           the Registrant and Microsoft Corporation.
 10.13+** OEM License Agreement dated July 27, 1995, between the Registrant and
           Netscape Communications Corporation, as amended by First Amendment,
           dated January 2, 1996, Second Amendment, effective January 2, 1996,
           and Third Amendment, dated May 21, 1996.
 10.14+   "Dial up Client" Agreement, dated August 21, 1995, between the
           Registrant and Netscape Communications Corporation.
 10.15+** "Internet Account Server" Participation Agreement, dated as of
           January 14, 1997, between the Registrant and Netscape Communications
           Corporation.
 10.16+   Special Customer Arrangement, dated May 17, 1996, between MCI
           Telecommunications Corporation and Sattel Communications LLC, as
           amended by First Amendment, dated July 2, 1996; assigned to
           Registrant by Assignment and Novation Agreement #2, dated as of
           August 7, 1996.
 10.17+   Master Agreement for MCI Enhanced Services, effective November 1,
           1996, between the Registrant and MCI Telecommunications Corporation.
 10.18+   Amended and Restated Employee Services and Staffing Agreement, dated
           June 19, 1997, between the Registrant and Critical Technologies,
           Inc., as amended on September 30, 1996, and October 23, 1996,
           including Colocation Services Agreement, dated as of November 1,
           1994, between the Registrant and Critical Technologies, Inc. and
           amendments thereto.
 10.19+   Amendment No. 3 to Internet Access Services Agreement, dated August
           23, 1996, between the Registrant and Intuit Inc.
 10.20+** Contract for Services, dated June 17, 1996, by and between the
           Registrant and MFS Telephone, Inc.
 10.21+** AT&T Contract Tariff Order, dated June 17, 1996, and Addendum of even
           date therewith.
</TABLE>    
 
                                      II-8
<PAGE>
 
<TABLE>   
 <C>      <S>
 10.22+   Master Lease Agreement Number CONO1C Between Concentric Research
           Corporation and Racal-Datacom, Inc. ("Racal"), dated August 4, 1994,
           as Supplemented by Letter Agreement, dated March 30, 1995, Between
           the Corporation and Racal.
 10.23+   Lease Agreement Number CON04C between Concentric Network Corporation
           and Racal-Datacom, Inc., dated June 26, 1996.
 10.24+   Master On-site Maintenance Plan Agreement Number CONO2C Between
           Concentric Research Corporation and Racal-Datacom, Inc., dated
           August 24, 1994.
 10.25**  Lease Agreement, dated November 1, 1996, effective March 11, 1996, by
           and between the Registrant and Saginaw Video Associates, d.b.a.
           Saginaw Conference Center.
 10.26**  Amended and Restated Lease Agreement, dated as of October 7, 1996,
           between the Registrant and Larry Shackley.
 10.27**  (Master) Lease, dated January 26, 1988, between Tandem Computers
           Incorporated and Spieker-French #130, Limited Partnership, as
           amended by Lease Amendment No. 1, effective February 5, 1990, and
           Extension Agreement, dated March 23, 1993.
 10.28**  Sublease, dated June 22, 1995, between the Registrant and Tandem
           Computers Incorporated.
 10.29**  Sublease, dated April 25, 1995, between Tandem Computers Incorporated
           and Passage Systems, Inc.
 10.30**  Assignment Agreement, dated December 6, 1996, by and between the
           Registrant and Passage Systems, Inc.
 10.31+   Internet Access Service Agreement, dated December 11, 1995, effective
           as of August 1, 1995, between the Registrant and Intuit, Inc., as
           amended.
 10.32+   Revised Virtual Private Network Services, dated February 1, 1997,
           between the Registrant and WebTV Networks, Inc.
 10.33+** Support Services Agreement, dated March 31, 1997, by and between the
           Registrant and MCI Telecommunications Corporation.
 10.34**  Note and Warrant Purchase Agreement, dated June 19, 1997, by and
           between the Registrant and Williams Communications Group, Inc.
           ("WCG")
 10.35**  Service Credits Letter Agreement, dated June 19, 1997, by and between
           the Registrant and WCG.
 10.36**  $1,100,000 Obligation Letter Agreement, dated June 19, 1997, between
           the Registrant and WCG.
 10.37**  Agency Agreement and Distribution Agreement, dated June 19, 1997,
           between the Registrant and WCG.
 10.38+   Co-Marketing Service Agreement, dated June 23, 1997 between the
           Registrant and Netscape Communications, Inc. ("Netscape")
 10.39+   Trademark License Agreement, dated June 23, 1997, between the
           Registrant and Netscape.
 10.40+** Software License Order Form, dated June 23, 1997, between the
           Registrant and Netscape.
 10.41**  Note and Warrant Purchase Agreement, dated June 23, 1997, between the
           Registrant, Kleiner Perkins, Caufield & Byers VII and KPCB
           Information Science Zaibatsu Fund VII.
 11.1**   Statement of computation of earnings per share.
 21.1**   List of Subsidiaries.
 23.1**   Consent of Wilson Sonsini Goodrich & Rosati, Professional Corporation
           (included in Exhibit 5.1).
 23.2     Consent of Ernst & Young, LLP, Independent Auditors.
 24.1**   Power of Attorney (see signature page).
 27.1**   Financial Data Schedule.
</TABLE>    
- --------
*  To be filed by amendment.
** Previously filed.
+  Certain information in these exhibits has been omitted and filed separately
   with the Securities and Exchange Commission pursuant to a confidential
   treatment request under 17 C.F.R. (S)(S) 200.80(b)(4), 200.83 and 230.46.
 
 
                                     II-9
<PAGE>
 
   (b) Financial Statement Schedules
 
     None.
 
ITEM 17. UNDERTAKINGS
 
  (a) The Registrant hereby undertakes to provide to the underwriter at the
closing specified in the underwriting agreements certificates in such
denominations and registered in such names as required by the underwriter to
permit prompt delivery to each purchaser.
 
  (b) Insofar as indemnification for liabilities arising under the Securities
Act of 1933 (the "Securities Act") may be permitted to directors, officers and
controlling persons of the Registrant pursuant to the foregoing provisions, or
otherwise, the Registrant has been advised that in the opinion of the
Securities and Exchange Commission such indemnification is against public
policy as expressed in the Securities Act and is, therefore, unenforceable. In
the event that a claim for indemnification against such liabilities (other
than payment by the Registrant of expenses incurred or paid by a director,
officer or controlling person of the Registrant in the successful defense of
any action, suit or proceeding) is asserted by such director, officer or
controlling person in connection with the securities being registered, the
Registrant will, unless in the opinion of its counsel the matter has been
settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.
 
  (c) The undersigned Registrant hereby undertakes that:
 
    (i)   For purposes of determining any liability under the Securities Act,
  the information omitted from the form of prospectus filed as part of this
  Registration Statement in reliance upon Rule 430A and contained in a form
  of prospectus filed by the Company pursuant to Rule 424(b)(1) or (4) or
  497(h) under the Securities Act shall be deemed to be part of this
  Registration Statement as of the time it was declared effective; and
 
    (ii)  For the purpose of determining any liability under the Securities
  Act, each post-effective amendment that contains a form of prospectus shall
  be deemed to be a new registration statement relating to the securities
  offered therein, and the offering of such securities at the time shall be
  deemed to be the initial bona fide offering thereof.
 
                                     II-10
<PAGE>
 
                                  SIGNATURES
   
  PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, AS AMENDED, THE
REGISTRANT CERTIFIES THAT IT HAS REASONABLE GROUNDS TO BELIEVE THAT IT MEETS
ALL THE REQUIREMENTS FOR FILING ON FORM S-1 AND HAS DULY CAUSED THIS AMENDMENT
NO. 5 TO REGISTRATION STATEMENT ON FORM S-1 TO BE SIGNED ON ITS BEHALF BY THE
UNDERSIGNED, THEREUNTO DULY AUTHORIZED, IN THE CITY OF CUPERTINO, STATE OF
CALIFORNIA, ON THE 31ST DAY OF JULY, 1997.     
 
                                          Concentric Network Corporation
                                                   
                                                /s/ Henry R. Nothhaft     
                                          By: _________________________________
                                                     HENRY R. NOTHHAFT
   
  PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, AS AMENDED, THIS
AMENDMENT NO. 5 TO REGISTRATION STATEMENT HAS BEEN SIGNED BELOW ON JULY 31,
1997, BY THE FOLLOWING PERSONS IN THE CAPACITIES INDICATED     
 
<TABLE>     
<CAPTION> 
              SIGNATURE                        TITLE                 DATE

<S>                                    <C>                      <C> 
                                       President and Chief          
     /s/ Henry R. Nothhaft              Executive Officer       July 31, 1997
- -------------------------------------   (Principal                       
          HENRY R. NOTHHAFT             Executive Officer),
                                        Director
 
                                       Chief Financial          July 31, 1997  
    /s/ Michael F. Anthofer             Officer (Principal      
- -------------------------------------   Financial and                     
         MICHAEL F. ANTHOFER            Accounting Officer)
 
                  *                    Director                 July 31, 1997  
- -------------------------------------                           
         TERENCE M. O'TOOLE                                              
 
                  *                    Director                 July 31, 1997  
- -------------------------------------                           
            VINOD KHOSLA                                                 
</TABLE>      

 
                                     II-11
<PAGE>
 
<TABLE>     
<CAPTION> 
 
             SIGNATURE                       TITLE                 DATE
<S>                                  <C>                       <C>   
                                      Director
- ------------------------------------
          RANDY A. MASLOW
 
                 *                    Director                 
- ------------------------------------                         July 31, 1997
            FRANCO REGIS                                       
 
                                      Director
- ------------------------------------
        LOUIS P. BENDER III
 
                 *                    Director                 
- ------------------------------------                         July 31, 1997
          GARY E. RIESCHEL                                     
 
                                      Director
- ------------------------------------
          ROBERT W. DOEDE


*By:________________________________  
        HENRY R. NOTHHAFT
         ATTORNEY-IN-FACT
</TABLE>      
 
                                     II-12
<PAGE>
 
                                 EXHIBIT INDEX
 
<TABLE>   
 <C>      <S>
  1.1**   Form of Underwriting Agreement.
  2.1**   Merger Agreement.
  3.1**   Form of Amended and Restated Certificate of Incorporation of
           Registrant prior to completion of this offering.
  3.2**   Form of Amended and Restated Certificate of Incorporation of
           Registrant to be effective upon completion of this offering.
  3.3**   Amended and Restated Bylaws of Registrant prior to completion of this
           offering.
  3.4**   Amended and Restated Bylaws of Registrant to be effective upon
           completion of this offering.
  4.1**   Form of Registrant's Common Stock Certificate.
  5.1**   Opinion of Wilson Sonsini Goodrich & Rosati, Professional
           Corporation, regarding legality of the securities being issued.
 10.1**   Amended and Restated Registration Rights Agreement, as amended and
           restated as of August 21, 1996, by and among the Registrant, GS
           Capital Partners, L.P., Kleiner Perkins Caufield & Byers VII,
           Comdisco, Inc., Intuit, Inc., certain listed holders of Series C
           Convertible Preferred Stock, certain listed holders of Common Stock,
           certain listed holders of Series D Convertible Preferred Stock, and
           Racal-Datacom, Inc.
 10.2**   Preferred Stock and Warrant Purchase Agreement, dated as of April 20,
           1995, by and among the Registrant, GS Capital Partners, L.P., and
           Kleiner Perkins Caufield & Byers VII and KPCB Information Sciences
           Zaibatsu Fund II, as amended.
 10.3**   Form of Director and Officer Indemnification Agreement.
 10.4**   1995 Stock Incentive Plan for Employees and Consultants, as amended
           February 21, 1996.
 10.5**   Amended and Restated 1996 Stock Plan.
 10.6**   1997 Stock Plan.
 10.7**   1997 Employee Stock Purchase Plan.
 10.8**   Termination of Services and Indemnification Agreement, dated as of
           February 15, 1996, by and between the Registrant and Marc Collins-
           Rector and Chad Shackley.
 10.9**   Agreement, dated as of February 15, 1996, by and between the
           Registrant and Randy Maslow.
 10.10**  Governance Agreement, dated May 15, 1997, by and among the
           Registrant, Marc Collins-Rector, Chad Shackley, GS Capital Partners,
           L.P., Kleiner Perkins Caufield & Byers VII, KPCB VII Founders Fund,
           KPCB Information Sciences Zaibatsu Fund II, and Intuit, Inc.
 10.11+** Employee Services and Staffing Agreement, dated November 1, 1995,
           between the Registrant and Critical Technologies, Inc., as amended
           on September 30, 1996, and October 23, 1996, including Colocation
           Services Agreement, dated as of November 1, 1994, between the
           Registrant and Critical Technologies, Inc. and amendments thereto.
 10.12+** Internet-Sign Up Wizard Referral and Microsoft Internet Explorer
           License and Distribution Agreement, dated March 28, 1997, between
           the Registrant and Microsoft Corporation.
 10.13+** OEM License Agreement dated July 27, 1995, between the Registrant and
           Netscape Communications Corporation, as amended by First Amendment,
           dated January 2, 1996, Second Amendment, effective January 2, 1996,
           and Third Amendment, dated May 21, 1996.
 10.14+   "Dial up Client" Agreement, dated August 21, 1995, between the
           Registrant and Netscape Communications Corporation.
 10.15+** "Internet Account Server" Participation Agreement, dated as of
           January 14, 1997, between the Registrant and Netscape Communications
           Corporation.
</TABLE>    
<PAGE>
 
<TABLE>   
 <C>      <S>
 10.16+   Special Customer Arrangement, dated May 17, 1996, between MCI
           Telecommunications Corporation and Sattel Communications LLC, as
           amended by First Amendment, dated July 2, 1996; assigned to
           Registrant by Assignment and Novation Agreement #2, dated as of
           August 7, 1996.
 10.17+   Master Agreement for MCI Enhanced Services, effective November 1,
           1996, between the Registrant and MCI Telecommunications Corporation.
 10.18+   Amended and Restated Employee Services and Staffing Agreement, dated
           June 19, 1997, between the Registrant and Critical Technologies,
           Inc., as amended on September 30, 1996, and October 23, 1996,
           including Colocation Services Agreement, dated as of November 1,
           1994, between the Registrant and Critical Technologies, Inc. and
           amendments thereto.
 10.19+   Amendment No. 3 to Internet Access Services Agreement, dated August
           23, 1996, between the Registrant and Intuit Inc.
 10.20+** Contract for Services, dated June 17, 1996, by and between the
           Registrant and MFS Telephone, Inc.
 10.21+** AT&T Contract Tariff Order, dated June 17, 1996, and Addendum of even
           date therewith.
 10.22+   Master Lease Agreement Number CONO1C Between Concentric Research
           Corporation and Racal-Datacom, Inc. ("Racal"), dated August 4, 1994,
           as Supplemented by Letter Agreement, dated March 30, 1995, Between
           the Corporation and Racal.
 10.23+   Lease Agreement Number CON04C between Concentric Network Corporation
           and Racal-Datacom, Inc., dated June 26, 1996.
 10.24+   Master On-site Maintenance Plan Agreement Number CONO2C Between
           Concentric Research Corporation and Racal-Datacom, Inc., dated
           August 24, 1994.
 10.25**  Lease Agreement, dated November 1, 1996, effective March 11, 1996, by
           and between the Registrant and Saginaw Video Associates, d.b.a.
           Saginaw Conference Center.
 10.26**  Amended and Restated Lease Agreement, dated as of October 7, 1996,
           between the Registrant and Larry Shackley.
 10.27**  (Master) Lease, dated January 26, 1988, between Tandem Computers
           Incorporated and Spieker-French #130, Limited Partnership, as
           amended by Lease Amendment No. 1, effective February 5, 1990, and
           Extension Agreement, dated March 23, 1993.
 10.28**  Sublease, dated June 22, 1995, between the Registrant and Tandem
           Computers Incorporated.
 10.29**  Sublease, dated April 25, 1995, between Tandem Computers Incorporated
           and Passage Systems, Inc.
 10.30**  Assignment Agreement, dated December 6, 1996, by and between the
           Registrant and Passage Systems, Inc.
 10.31+   Internet Access Service Agreement, dated December 11, 1995, effective
           as of August 1, 1995, between the Registrant and Intuit, Inc., as
           amended.
 10.32+   Revised Virtual Private Network Services, dated February 1, 1997,
           between the Registrant and WebTV Networks, Inc.
 10.33+** Support Services Agreement, dated March 31, 1997, by and between the
           Registrant and MCI Telecommunications Corporation.
 10.34**  Note and Warrant Purchase Agreement, dated June 19, 1997, by and
           between the Registrant and Williams Communications Group, Inc.
           ("WCG")
 10.35**  Service Credits Letter Agreement, dated June 19, 1997, by and between
           the Registrant and WCG.
 10.36**  $1,100,000 Obligation Letter Agreement, dated June 19, 1997, between
           the Registrant and WCG.
 10.37**  Agency Agreement and Distribution Agreement, dated June 19, 1997,
           between the Registrant and WCG.
 10.38+   Co-Marketing Service Agreement, dated June 23, 1997 between the
           Registrant and Netscape Communications, Inc. ("Netscape")
 10.39+   Trademark License Agreement, dated June 23, 1997, between the
           Registrant and Netscape.
</TABLE>    
<PAGE>
 
<TABLE>   
 <C>      <S>
 10.40+** Software License Order Form, dated June 23, 1997, between the
           Registrant and Netscape.
 10.41**  Note and Warrant Purchase Agreement, dated June 23, 1997, between the
           Registrant, Kleiner Perkins, Caufield & Byers VII and KPCB
           Information Science Zaibatsu Fund VII.
 11.1**   Statement of computation of earnings per share.
 21.1**   List of Subsidiaries.
 23.1**   Consent of Wilson Sonsini Goodrich & Rosati, Professional Corporation
           (included in Exhibit 5.1).
 23.2     Consent of Ernst & Young, LLP, Independent Auditors.
 24.1**   Power of Attorney (see signature page).
 27.1**   Financial Data Schedule.
</TABLE>    
- --------
*  To be filed by amendment.
** Previously filed.
+  Certain information in these exhibits has been omitted and filed separately
   with the Securities and Exchange Commission pursuant to a confidential
   treatment request under 17 C.F.R. (S)(S) 200.80(b)(4), 200.83 and 230.46.

<PAGE>
 
                                                                   EXHIBIT 10.14

                      NETSCAPE COMMUNICATIONS CORPORATION
                                      AND
                        CONCENTRIC RESEARCH CORPORATION
                          "DIAL-UP CLIENT" AGREEMENT


     This Agreement is made as of August 21, 1995 ("Effective Date") between
Netscape Communications Corporation a Delaware corporation with its principal
place of business 501 East Middlefield Road, Mountain View, CA 94043
("Netscape") and Concentric Research Corporation, a Florida corporation with a
place of business at 10590 N. Tantau Avenue, Cupertino, CA 95014 ("Concentric").

     A.  Netscape develops and markets technology and services for use in
connection with the Internet.  Netscape has a client/server product ("Dial-Up
Client Product") that operates as a component of a system ("Dial-Up System")
that allows Internet users in the U.S. to select, and register with, an Internet
access provider from a menu of Internet access providers that have entered into
agreements with Netscape.

     B.  Concentric is an Internet access provider that wishes to be included in
the menu of Internet access providers used with the Dial-Up System ("Menu") so
that users of its Internet access services may register through the Dial-Up
System ("Subscribers").

     Netscape and Concentric agree as follows:

     1.  Dial-Up Client Product.  The current descriptions of the Dial-Up Client
         ----------------------                                                 
Product and the Dial-Up System are contained in Attachment A.  Concentric
acknowledges that these may be revised by Netscape from time to time in response
to market conditions.  Netscape will issue specific written procedures for the
use of the Dial-Up System.  Concentric's use of the Dial-Up System will be in
accordance with the terms of this Agreement, including Attachment A, and
Netscape's written procedures.  Netscape will use reasonable commercial efforts
to implement the Dial-Up System in the U.S., and Concentric will use reasonable
commercial efforts to assist Netscape in doing so.

     2.  Menu of Internet Access Providers.  Subject to the terms and conditions
         ---------------------------------                                      
of this Agreement (including Concentric's payment in full of the commissions,
the development expenses, and toll-free telephone charges specified in Sections
7(a), (c) and (d), respectively), Netscape will include Concentric in the Menu.
Concentric acknowledges that Netscape will determine the format, ordering, and
contents of the Menu (including the total number of Internet access providers
listed in the Menu at any time) in its sole discretion, and may revise such
format, ordering, and contents at any time.  Netscape will use reasonable
commercial efforts to remain neutral with respect to the choices of providers
made by users of standard Netscape Navigator Personal Edition and any updates
thereof.

     3.  Concentric Infrastructure Deliverables.
         -------------------------------------- 

         3.1  Requirements for Internet Access Infrastructure.  Netscape 
              -----------------------------------------------  
requires that Concentric establish and maintain, and Concentric agrees to
establish and maintain, the infrastructure
<PAGE>
 
for Internet access as described in Attachment B in order that Netscape may
provide Subscribers with the choices of competitive Internet access services.

     3.2  Concentric Deliverables.
          ----------------------- 

          3.2.1  Provider Pages.
                 -------------- 

                 (a) Function of Provider Pages.  When a user of the Dial-Up 
                     --------------------------  
Client Product wishes to learn about a specific Internet service provider, the
user may select such provider from the Menu and will then be linked to one or
more informational HTML pages and data sheets containing such provider's fee
schedule and describing its service offerings ("Provider Pages"), which are
intended to aid the user in deciding which provider to subscribe to.

                 (b) Delivery of Provider Pages.  Concentric will deliver to 
                     -------------------------- 
Netscape, within ten (10) days of Netscape's provision of the appropriate form
to Concentric, the Provider Pages of Concentric in final form, a copy of which
is to be attached as part of Section 2.1 of Attachment B, for incorporation into
the Dial-Up System. Concentric may update its Provider Pages up to once each
month by delivering revised pages to Netscape in final form by the 25th day of
the previous month. Netscape will use reasonable commercial efforts to update
the Dial-Up System with such revised pages within ten (10) days of their
delivery by Concentric, subject to subsection (c) below.

                 (c) Review and Approval of Provider Pages.  Netscape will have 
                     -------------------------------------  
the right to review the contents and format of each Provider Page prior to
including any such page in the Dial-Up System. If Netscape determines, in its
sole discretion, at any time before or after delivery of any such page by
Concentric that such page contains any material, or presents any material in a
manner, that is not appropriate for use in the Dial-Up System, Netscape will
inform Concentric of such determination and, if such page is already
incorporated in the Dial-Up System, Netscape may immediately remove such page
from the Dial-Up System. Instead of Netscape incorporating such Provider Page in
the Dial-Up System, Concentric will deliver to Netscape a revised Provider Page
that Netscape determines, in its sole discretion, is appropriate for use in the
Dial-Up System. In no event will Netscape be required to incorporate any
Provider Page or other information in the Dial-Up System except as described in
this paragraph.

                 (d) Credit System Interface.  Concentric will deliver to 
                     -----------------------
Netscape within five (5) days of the Effective Date the specifications and other
information needed by Netscape to interface with Concentric's designated credit
and approval system. Concentric will provide Netscape with any and all updates
to such information on a timely basis. Any implementation which Netscape creates
in the development of such an interface will be owned by Netscape.

          3.2.2  Other Concentric Deliverables.  Additionally, Concentric will
                 -----------------------------                                
provide Netscape with other deliverables as described in Attachment A.

                                      -2-
<PAGE>
 
     4.  License Rights.  Concentric grants to Netscape a non-exclusive license
         --------------                                                        
during the term of this Agreement to use, reproduce, electronically distribute,
publicly display, and publicly perform the materials delivered to Netscape by
Concentric in connection with the Dial-Up System. Nothing in this Agreement
gives either party any exclusive marketing or distribution rights.

     5.  Marketing and Promotion.
         ----------------------- 

         (a) Marketing.  Netscape will determine in its sole discretion the 
             ---------      
manner of, and resources it will devote to, advertising, promoting, and
otherwise marketing the Dial-Up Client Product under this Agreement. Concentric
acknowledges that the commercial success of the Dial-Up Client Product is highly
speculative and that Netscape has made no representation to Concentric that
Concentric will obtain any Subscribers through the use of the Dial-Up Client
Product. Concentric agrees to participate in press announcements regarding the
creation and deployment of the Dial-Up System as reasonably requested by
Netscape.

         (b) Trademark Usage in Marketing Materials.  Netscape will have the 
             --------------------------------------
right to use Concentric's trademarks, trade names, servicemarks, and/or logos in
any advertising, promotional, and other marketing materials for the Dial-Up
Client Product and the Dial-Up System in a manner consistent with Concentric's
standard trademark usage. Netscape will submit samples of such materials to
Concentric from time to time upon Concentric's request.

         (c) Promotions.  Concentric will offer a free trial period of at least 
             ----------    
five (5) hours of connect time to each Subscriber during the term of this
Agreement.

     6.  Technical Support.  Netscape will provide front line (first line)
         -----------------                                                
technical support to users of the Dial-Up Client Product during the registration
process.  Concentric agrees to provide back-up (second line) technical support
to Netscape during the registration process.  Concentric will have primary
responsibility for end user support for Internet access services once the user
has established a functioning connection directly to the Concentric.  All other
aspects of technical support under this Agreement will be as specified in
Attachment C.

     7.  Payments.
         -------- 

         (a) Commissions.  Concentric agrees to pay Netscape a commission for 
             ----------- 
each new Subscriber. The amount of each commission will be calculated as
specified in Attachment and will accrue as to each Subscriber upon Concentric
billing such Subscriber for such Subscriber's second month of service from
Concentric. Concentric will pay Netscape commissions on a calendar month basis
within fifteen (15) days of the end of the month in which the commission
accrued. The payment may be made either (i) with the monthly report required to
be submitted by Concentric under Section 8 below or (ii) by electronic wire
transfer to an account designated by Netscape.

         (b) Equipment Required for Concentric.  Concentric agrees to ensure 
             ---------------------------------    
that all incremental requirements necessary to establish communication links
between Concentric's registration system and the Netscape registration server
are promptly performed by Concentric at

                                      -3-
<PAGE>
 
Concentric's sole cost and expense. Typically such requirements will include,
without limitation, a router and telecommunications equipment required by
Concentric.

         (c) Development Expenses.  Concentric agrees to pay Netscape the 
             --------------------
expenses incurred by Netscape in modifying the Dial-Up System to make it
properly interface with Concentric's access set-up system. The type and amount
of such development expenses and the development schedule is to be mutually
agreed to by the parties and to be attached as part of Attachment B. Netscape
will own all modifications to the Dial-Up System.

         (d) Toll-Free Telephone Charges.  Each month, Netscape will bill
             ---------------------------                                 
Concentric, and Concentric will pay Netscape [*] Concentric will pay the Toll
Charges within fifteen (15) days upon receipt of invoice from Netscape.
Concentric shall have the right, no more than once per twelve month period, to
have an independent third party verify that the amount of the Toll Charges
billed to Concentric is correct, or if incorrect, the amount which such third
party believes Concentric should have been charged. Concentric shall not have
the right to learn the total number of new Subscribers for the Internet access
providers on the Dial-Up System.

     8.  Records and Reports.  Within fifteen (15) days of the end of each
         -------------------                                              
month, Concentric will deliver to Netscape a written report in the format as
specified in Attachment E showing the number of Subscribers acquired by
Concentric through the Dial-Up System, the number of Subscribers which
Concentric billed for an initial month's service, the number of Subscribers
Concentric billed for a second month's service, and such other information as
Netscape may reasonably request from time to time.  Only in case commission
payments are made via electronic wire transfer, Concentric may submit to
Netscape the required monthly report by fax or e-mail. Otherwise, commission
payments must accompany the monthly report.  Concentric will maintain, for at
least three (3) years after expiration or termination of this Agreement,
accurate books and records relating to Subscribers who first registered for
Concentric's services through the Dial-Up Client Product, and will permit
examination of such records by Netscape at reasonable times.

     9.  Subscriber Fees and Terms.  Concentric will determine its Internet
         -------------------------                                         
subscription fees and the terms of its service offerings in its sole discretion.

     10. Confidential Information.  Confidential information of each party
         ------------------------                                         
disclosed in connection with this Agreement ("Confidential Information") will be
treated as specified in the agreement contained in Attachment F.  In the event
such agreement terminates or expires, its terms will continue to govern the
Confidential Information.  The identity of each party's customers will be the
Confidential Information of such party.  Concentric Confidential Information
shall include the records and reports described in Section 8 above ("Reports")
which are not available to Netscape through other sources, provided that
Netscape may aggregate the information in Reports with 

- ------------------
         [*] Certain information on this page has been omitted and filed
separately with the Securities and Exchange Commission. Confidential treatment
has been requested with respect to the omitted portions.



                                      -4-
<PAGE>
 
information from other sources in such a manner that the origin of Concentric's
information is not readily available, and the aggregated information shall not
be Concentric Confidential Information.

     11.  Indemnity.  Each party will defend, indemnify, and hold the other
          ---------                                                        
party harmless against any third party claims arising from the manufacture, use,
reproduction, or distribution, as authorized in this Agreement, of any
technology, content, or other information supplied by it to the other party
under this Agreement, including but not limited to arising out of any alleged
infringement or misappropriation of any copyright, trademark, trade secret,
patent, or other intellectual property right, or violation of any right of
privacy or publicity.

     12.  Proprietary Rights.
          ------------------ 

          (a) Ownership.  Concentric acknowledges that Netscape and its 
              ---------  
licensors own all right, title, and interest in and to the Dial-Up Client
Product and the other components of the Dial-Up System. Netscape acknowledges
that Concentric and its licensors own all right, title, and interest in and to
Concentric's Internet access system.

          (b) No Right to Use.  Nothing in this Agreement gives Concentric any 
              ---------------
right or license to use, reproduce, or distribute any technology or intellectual
property rights in the Dial-Up System or otherwise belonging to Netscape.
Except for Netscape's right to make use of the Concentric Pages and Concentric's
trademarks, trade names, servicemarks, logos and other materials as specified in
this Agreement, nothing in this Agreement will give Netscape any right or
license to use, reproduce, or distribute any technology or intellectual property
rights in Concentric's Internet access system or otherwise belonging to
Concentric.

     13.  Term and Termination of Agreement.
          ----------------------- --------- 

          (a) Term. This Agreement is for a period of one year beginning on the
              ----                                                             
Effective Date, at which time it will automatically renew subject to Section
13(b).

          (b) Termination at Will.  Either party may terminate this Agreement at
              -------------------   
will at any time during the term of this Agreement with or without cause, by
written notice given to the other party given not less than thirty (30) days
prior to the effective date of such termination.

          (c) Commission Rights on Termination or Expiration.  Following 
              ---------------------------------------------- 
termination or expiration of this Agreement, Concentric will pay to Netscape all
commissions not yet paid on all Subscribers who registered with Concentric
through the Dial-Up Client System at any time prior to the termination or
expiration of this Agreement, regardless of when Concentric's obligation to pay
such commission accrues.

          (d) Development Expenses Incurred Prior to Termination.  If this 
              --------------------------------------------------
Agreement is terminated prior to expiration, and the development expenses
incurred by Netscape under Section 7 above have not been fully paid prior to
such early termination, Concentric will pay to Netscape such percentage of the
total development expenses as is determined by the ratio of the actual time that

                                      -5-
<PAGE>
 
Netscape has spent on modifying the Dial-Up System pursuant to Section 7 prior
to such early termination divided by the total, planned development time.

          (e) Survival.  Sections 7, 8, 10, 11, 12, 13(c), 14 will survive
              --------                                                    
termination or expiration of this Agreement.

     14.  Limitation of Liability.  EXCEPT FOR EACH PARTY'S OBLIGATIONS UNDER
          -----------------------                                            
SECTION 11, IN NO EVENT WILL EITHER PARTY BE LIABLE FOR ANY LOST PROFITS OR ANY
FORM OF SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES FROM ANY CAUSES OF ACTION
OF ANY KIND, WHETHER ARISING IN TORT (INCLUDING NEGLIGENCE), CONTRACT, OR
OTHERWISE, EVEN IF IT HAS BEEN INFORMED IN ADVANCE OF THE POSSIBILITY OF SUCH
DAMAGES.  NETSCAPE WILL HAVE NO LIABILITY FOR ANY UNAUTHORIZED TRANSACTIONS OR
OTHER ACTIVITY ON PROVIDER'S CREDIT CARD APPROVAL SYSTEM.  IN NO EVENT WILL
NETSCAPE'S TOTAL LIABILITY UNDER THIS AGREEMENT EXCEED THE TOTAL AMOUNTS PAID TO
IT BY PROVIDER UNDER, OR IN CONNECTION WITH, THIS AGREEMENT.

     15.  General.
          ------- 

          (a) Assignment.  This Agreement is not assignable by either party, 
              ----------   
except that either party may assign this Agreement to an entity controlling,
controlled by, or under common control with it or to any entity that acquires
all or substantially all of such party's assets, or into which it is merged or
otherwise reorganized. Any attempted assignment in violation of this paragraph
will be void. The provisions of this Agreement will be binding upon and inure to
the benefit of the parties, their successors, and permitted assigns.

          (b) Independent Contractor.  Netscape's relationship with Concentric 
              ----------------------
during the term of this Agreement will be that of an independent contractor, and
not a partner or joint venturer.

          (c) Notices.  All notices and demands under this Agreement will be in
              -------                                                          
writing and will be delivered by personal service, confirmed fax, confirmed e-
mail, express courier, or certified mail, return receipt requested, to the
address of the receiving party set forth in this Agreement (or at such different
address as may be designated by such party by written notice to the other
party), and will be effective upon receipt.

          (d) Governing Law and Venue.  The laws of the State of California,
              -----------------------                                       
excluding that body of law controlling conflicts of law, will govern all
disputes arising out of or relating to this Agreement.  Each party hereby
consents to personal jurisdiction and service of process on it in the State of
California and waives any right to object thereto.

          (e) Compliance with Law.  Each party will at all times comply with all
              -------------------                                               
applicable international, national, state, regional, and local laws and
regulations, including U.S. export control laws, in performing its duties under
this Agreement.

                                      -6-
<PAGE>
 
          (f) Force Majeure.  Neither party will be responsible for any failure 
              -------------
to perform its obligations under this Agreement due to causes beyond its
reasonable control, including but not limited to acts of God, war, riot,
embargoes, acts of civil or military authorities, fire, floods, accidents,
strikes, or shortages of transportation, facilities, fuel, energy, labor or
materials.

          (g) Waiver.  The waiver by either party of any breach of this 
              ------ 
Agreement by the other party will not waive subsequent defaults by such party of
the same or a different kind.

          (h) Severability.  In the event any provision of this Agreement is 
              ------------  
held by a court or other tribunal of competent jurisdiction to be unenforceable,
the other provisions of this Agreement will remain in full force and effect.

          (i) Publicity.  Neither party will disclose any of the terms of this
              ---------                                                       
Agreement to any third party.  Netscape and Concentric shall cooperate with each
other so that each party may issue a press release concerning this Agreement,
provided that each party must approve any press release prior to its release.
Concentric will not disclose the existence of this Agreement until after
Netscape publicly issues such press release.

          (j) Entire Agreement.  This Agreement, together with its attachments,
              ----------------                                                 
constitutes the complete and exclusive agreement between the parties pertaining
to the subject matter hereof, and supersedes in its entirety any and all prior
written or oral agreements or communications between the parties with respect to
such subject matter.  Concentric acknowledges that it is not entering into this
Agreement on the basis of any representations not expressly contained herein.
Any modifications or waivers under this Agreement must be in writing and signed
by both parties.

                                      -7-
<PAGE>
 
     The parties have executed this Agreement as of the Effective Date.

CONCENTRIC RESEARCH CORPORATION            NETSCAPE COMMUNICATIONS
                                           CORPORATION


Signature: /s/ Peter J. Bergeron           Signature: /s/ Conway Rulon-Miller
          -------------------------                  ---------------------------

Name: Peter J. Bergeron                    Name: Conway (Todd) Rulon-Miller
     ------------------------------             --------------------------------

Title: Secretary                           Title: VP Soler
      -----------------------------              -------------------------------

Date: 8/21/95                              Date: 8/24/95
     ------------------------------             --------------------------------

                                      -8-
<PAGE>
 
                                 ATTACHMENT A

             DIAL-UP CLIENT PRODUCT AND DIAL-UP SYSTEM DESCRIPTION
             -----------------------------------------------------

     [The document titled "Milan Customer Registration Process-Release 1.1" is
to be attached here.]
<PAGE>
 
                MILAN CUSTOMER REGISTRATION PROCESS-RELEASE 1.1

INTRODUCTION

     This document describes process by which a Milan customer is registered and
     signed up with an internet service provider (ISP). It covers all functional
     and technical aspects of the process from the customer's PC to Netscape's
     registration server (RS) to the ISP's account creation process. The scope
     of this discussion does not include the Milan software installation process
     from diskette to the customer's PC.

BACKGROUND

     Netscape's new retail product, Netscape Navigator Personal Edition (coded
     named Milan), is a web browser geared towards novice and experienced home
     users who want to access the Internet. Packaged with Milan is a TCP/IP
     stack and a dialer which is used to establish a modem-based PPP connection
     to an ISP.
     
     The main goal of Milan is to make connecting to the Internet as easy as
     possible for the customer, so that they do not need to know the
     complexities of TCP/IP, PPP and the underlying connection. To this end,
     when the customer starts Milan, it automatically initiates the dialer,
     calls the ISP and established the connection.

     However, before Milan can be used, the software must be registered with
     Netscape, the PC must be configured, and an account with an ISP /(1)/ must
     be created. The next section describes the customer registration program
     which automates this process.

CUSTOMER REGISTRATION PROCESS 

     Provided with Milan is a separate Windows-based customer registration
     program (CRP) used to gather customer information, sign-up the user with an
     ISP of their choice and configure their PC. The CRP is started by the
     installation program after the software is installed on the PC.  The CRP 
     does the following things:

             .  Gathers customer information
             .  Customer survey (optional)
             .  Configures modem
             .  Starts the Netscape Navigator for ISP selection and registration
                process
             .  Saves ISP settings and creates icon for connecting to ISP

     Gather Customer Information

     In this step, the CRP gathers information about the customer such as name,
     address and phone number. This information is used to register the customer
     with Netscape (for support purposes), build Netscape's customer database
     and create the ISP account. See Appendix A for a specification of the
                                     ----------
     information that is gathered.

     Customer Survey

     In this (optional) step, the CRP asks the customer to fill out a survey to
     obtain marketing and demographic information about Netscape's customers
     such as what they will use Milan for, their age and income. See Appendix B
                                                                     ----------
     for a specification of the survey information that is gathered.

__________________
/1/ Milan is aimed at those home users who do not yet have internet accounts
or ISP access. Users that already have an ISP account and want to use Milan can
consult a technical appendix which describes the necessary actions to configure
their machine.

<PAGE>
 
Configure Modem

In this step, the CRP tries to determine the configuration of the customer's 
modem.  If it cannot auto-detect it, it then prompts the user to enter the 
information.  The needed parameters are the following:

          .  Baud rate
          .  Communications port
          .  Initialization string

The configuration parameters are needed so that the Milan dialer can properly 
operate the modem.

ISP Selection

In this step, the CRP starts the Navigator in Registration/Kiosk mode.  The 
Navigator uses the dialer to call a toll-free 800/2/ number and establish a PPP 
connection to the Netscape's Registration Server (RS).  User verification will 
be done with the PAP protocol and a fixed username and password.  Having 
established this connection, the full capabilities of Navigator are used to 
complete the rest of the registration process.

When the Navigator is in Kiosk mode (-k command line option), all of the menus 
and toolbars on the main Netscape window are disabled.  This prevents the 
customer from navigating through any means outside the hypertext links found in 
the documents.  Kiosk mode is a general purpose option of the Netscape client.  
In the case of the registration process, it is used to guarantee that the user 
has to take the registration pages in the order that they were intended.

The Registration mode (-r command line option) of the Navigator is only enabled
in the Milan version of the Navigator.  Its sole purpose is to enable the 
automatic registration process described in this document.  A client loaded in 
registration mode will also enable the Navigator to receive and parse 
registration data returned from the RS.

The first action taken by the Navigator in registration mode is to post the 
customer and survey information gathered by the CRP to the RS URL.  This 
overrides any homepage setting or other command-line options.  The default RS 
URL is stored in an INI file which provides us the flexibility to change this 
dynamically for testing purposes or different versions of Milan.

The RS then responds with the ISP home page, from which the user can select the 
ISP of their choice.  Once a particular ISP is selected, a forms page is 
presented to gather any additional user  information (e.g., account name) needed
to setup the ISP account.  This information is submitted to the RS, which then 
sets up the account with the chosen ISP.  See the section entitled RS 
                                                                   --
Functionality for more detail on the actions performed by the RS.
- -------------
The account information and a Windows icon for the ISP is returned by the RS to 
the Navigator.  See Appendix D for details on format of the stream returned to 
                    ----------
the Navigator.

Save Information and Create Icon

After the account is successfully setup through the Navigator, the line to the 
RS is dropped and the ISP information is passed back to the CRP.  The CRP saves 
the ISP information and configures a Windows icon for starting the dialer and 
connecting to the ISP.  This completes the registration process.  Subsequently, 
the customer only needs to connect to the ISP and  then start the navigator.



_______________________

/1/ The number is 1-800-638-8290.

                    







                                                                    

<PAGE>
 
RS FUNCTIONALITY

     After connecting, the Navigator sends the RS a form-post URL containing the
     customer and survey information (see Appendices A and B) which the RS saves
                                          ------------------
     in a log file. It then sends back the ISP Selection home page. Each ISP may
     have a page(s) which describe their service offerings. Once the customer
     has decided on a particular ISP, he must fill out a form with the data
     required by the ISP to establish an account. The user does not have to re-
     enter any data entered in the CRP (e.g., name, address). The additional
     data required by each ISP varies, but can include such things as:

          .  Desired account name
          .  Password
          .  Keyword

     After the customer submits the ISP data, the RS establishes a connection 
     with the ISP and attempts to setup the user account.  

     In some cases, the ISP may require more information or a clarification. In
     such cases, the RS sends back a form page requesting the desired
     information. When the user resubmits the form, the RS sends it back to the
     ISP.

     When the account setup is successful, the account information is returned 
     to the Navigator.  The information returned and its format is documented in
     Appendix D.
     ----------

OVERALL ARCHITECTURE

     This section describes the technical details of the RS implementation.  
     Figure 1 represents all the components involved in this process.

                            [GRAPHIC APPEARS HERE]
       
                  

                  Figure 1 - Registration Process Components

     The overall functionality and flow of activity was described in the
     previous sections. The proceeding sections describe the technical details
     of each component and the interfaces between each component.

MILAN CLIENT

                            [DIAGRAM APPEARS HERE]

     As described in the preceding sections, the main client components used
     during the registration process are the CRP, Navigator and Dialer. Figure 2
     shows these components.








<PAGE>

                                    Milan 
[*]

* Certain information in this Exhibit has been omitted and filed separately with
  the Securities and Exchange Commission. A total of 3 pages has been omitted.
  Confidential treatment has been requested with respect to the omitted 
  portions.
<PAGE>
 
     If the user chooses to cancel at any point, a fail message is sent in a
     MIME stream and the customer information is moved from the reg-attempt file
     into the reg-cancel file. All of the reg-* files are described in
     Appendix E. 
     ----------
 
     Detailed information about the internal workings of the CGI script and the
     communication with each ISP is documented in the Netscape Registration
                                                      ---------------------  
     Server Technical Design document.
     -----------------------

SUMMARY

     This document has explained all of the interfaces in the customer
     registration process. All code for the Signup, Navigator and RS
     applications has been written to conform to the information in this
     document.

<PAGE>
 
Appendix A - Milan Customer Information

[*]

Certain information in this Exhibit has been omitted and filed separately with 
the Securities and Exchange Commission. A total of 9 pages has been omitted. 
Confidential treatment has been requested with respect to the omitted portions.
<PAGE>
 
                                  ATTACHMENT B

         CONCENTRIC INFRASTRUCTURE/DELIVERABLES & DEVELOPMENT EXPENSES
         -------------------------------------------------------------


     1.   Concentric Infrastructure for Internet Access
          ---------------------------------------------

          (a)  Nationwide coverage with local access in at least 100 Points of
Presence (POPs)

          (b)  PPP support- UNIX based registration process running at
Concentric

          (c)  Ability to do on-line credit card authorization and billing

          (d)  support for POP3 or SMTP mail servers

          (e)  Support for NNTP for news

          (f)  Account for testing dialer and Netscape Navigator connection, as
specified below, to be delivered within five (5) business days after the
Effective Date:

               (i)    Concentric test accounts for testing the dialer and
Netscape Navigator on the Concentric network.

               (ii)   A specification of the protocol used to create Concentric
Internet accounts over a TCP/IP connection.  Typically, such a protocol
describes the "language" spoken by Concentric's registration server and how
Netscape needs to interact with it.

               (iii)  A list of the required data items used to create accounts
(this may be part of the protocol).

               (iv)   An Concentric contact for dealing with protocol,
implementation and testing problems/issues.

               (v)    A means to test communication/' interaction between
Netscape's registration server and Concentric's. Ideally, this is a specific
Concentric test machine to which Netscape has access over the Internet.

               (vi)   A means to create "free" test accounts on Concentric's
registration server.  This is used for testing and promotional purposes.

     2.   Concentric Deliverables.
          ----------------------- 

          2.1  Provider Page.  [See Attachment B-I for Concentric's Provider
               -------------                                                
Page]
<PAGE>
 
          2.2  Other Concentric Deliverables.
               ----------------------------- 

               (a) Information on Concentric's platform on which its
registration server runs. This is required for Netscape to provide the
Concentric with SSLD for Concentric's registration server.

               (b) A description of Concentric's services and prices. In
addition, Concentric must provide Netscape with an Concentric logo (gif format)
and a Wi/n/dows 32x32 icon. The logo is used to represent Concentric on the
registration server pages, and the icon is used on the client side for the
dialer.

               (c) A list of POPs

               (d) Contact for updates and changes to the POPs

               (e) in' automated process to update the POP numbers Netscape
displays to users; and an updated list each time a new POP becomes effective.

          3.
          Development Expenses.
          -------------------- 

          [*]

- --------------------------

          [*]Certain information on this page has been omitted and filed
separately with the Securities and Exchange Commission. Confidential treatment
has been requested with respect to the omitted portions.

                                      -2-
<PAGE>
 
                                 ATTACHMENT B-1

Netscape pricing sheet plan

<TABLE>
<CAPTION>
 
- --------------------------------------------------------------------------------
                             The Concentric Network
                             If you have questions, call (800) 745-2747
- --------------------------------------------------------------------------------
<S>                          <C>
Promotional offers           Buy one month, get the second month free.  Never a
                             start-up fee.  Your choice of four pricing plans,
                             rates apply 24 hours a day, 7 days a week.
- --------------------------------------------------------------------------------
Unlimited Plan               US $29.95 per month for unlimited connect time
- --------------------------------------------------------------------------------
Hourly Plan                  US $19.95 per month for 20 hours; additional hours
                             $1.50.
- --------------------------------------------------------------------------------
Beginner's Plan              US $7.95 per month for 5 hours; additional hours
                             $1.95
- --------------------------------------------------------------------------------
Toll-Free Plan               US $10 per month for 2 hours; additional hours $5
- --------------------------------------------------------------------------------
Start-up fee (all plans)     $0 
- --------------------------------------------------------------------------------
Customer Support             24 hours a day, 7 days a week (800) 745-2747
- --------------------------------------------------------------------------------
</TABLE>

Concentric Network
Key Advantages

 .    With flat rate service, unlimited connect time for one low monthly price.
 .    Low hourly fee plans for light users.
 .    Never a start-up fee.
 .    Rates apply 24 hours a day, 7 days a week.
 .    Up to 5 megs of storage space for your FREE personal WWW page
 .    24-hour, 7-day a week Customer Service
 .    135 dial-in nodes nationwide (Expanding to 242 soon).

Terms & Conditions

Once you are signed on, please read our terms of service at
http://WWW.cris.com/terms.  If you do not agree on our terms of service, please
call (800) 745-2747 to cancel your account.
<PAGE>
 
                                  ATTACHMENT C

                          ISP TECHNICAL SUPPORT TERMS


     1.   Netscape will provide front-level support to a potential Subscriber
during the installation process for the Dial-up Client and the initial
registration with Provider.  Provider will provide back-line support to
Netscape.

     2.   Beginning on the conclusion of the registration process, Provider will
be responsible for all Subscriber support relating to Internet access services.

     3.   Following the conclusion of the registration process, Provider will
provide each new Subscriber with a copy of Provider's terms and conditions of
service for review by Subscriber.

     4.   Provider and Netscape will each provide front-line support of the
Dial-Up Client to the Subscriber free of charge for ninety (90) days after the
Subscriber registers with Provider (the Initial Support Period).  Such support
includes call receipt, entitlement verification, call screening, installation
assistance, problem identification and diagnosis.  Provider will assign an
adequate number of properly qualified and trained personnel to provide front-
line support for the Dial-Up Client.  If Netscape support representatives are
being contacted by Provider for front line support or Internet access questions,
or for excessive back line support then, upon Netscape's request, Provider and
Netscape will cooperate to minimize such contact.

     5.   Netscape will provide back-end support for the Dial-Up Client to
Provider (as well as front end support to Subscribers described in Section 4
above).  Back-end support to Provider includes efforts to identify defective
source code and to provide corrections, workarounds and/or patches to
reproducible deviations in the Dial-Up Client from the applicable specifications
shown in the applicable reference manuals ("Program Errors").

          (a) Netscape will provide Provider with a telephone number and an e-
mail address which Provider may use to report Program Errors during Netscape's
local California business hours (8am - 5pm PST).  Provider will provide
sufficient information for Netscape to enable Netscape to duplicate the Program
Error.  At any given time, Netscape will provide back line support to Provider
for the then-current version of the Dial-Up Client, and for the immediately
preceding version until it has been superseded for a period of six (6) months.

          (b) Provider will identify one (1) member of its customer support
staff and one (1) alternate to act as the primary technical liaisons responsible
for all communications with Netscape's support representatives.  Such liaisons
will have sufficient technical expertise, training and/or experience, for
Provider to perform its obligations hereunder.  Provider may substitute contacts
at any time by providing one (1) week's prior written and/or electronic notice
thereof to Netscape. Provider's initial liaison(s) are:
<PAGE>
 
          _________________________ and _________________________
                    primary                   alternate

          6.  Following the Initial Support Period, each of Netscape and
Provider may, in its discretion, stop offering Subscriber support, continue to
offer Subscriber support free of charge, or may charge for Subscriber support.

                                      -3-
<PAGE>
 
                                  ATTACHMENT D

                                COMMISSION RATES
                                ----------------


[*]

- ---------------------------

     [*]  Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission. A total of 1 page containing such
information has been omitted from this exhibit. Confidential treatment has been
requested with respect to the omitted portions.
<PAGE>
 
                                  ATTACHMENT E

                                 REPORT FORMAT
                                 -------------

                                                         Number of Subscribers
Subscribers billed 1st        Subscribers billed 2nd      via Dial-Up System
        month                          month              Since Effective Date
- ----------------------        ----------------------     ---------------------- 
<PAGE>
 
                                  ATTACHMENT F

                    MUTUAL CONFIDENTIAL DISCLOSURE AGREEMENT


          WHEREAS, Netscape Communications Corporation ("Netscape") has
developed unique and proprietary computer programs; and

          WHEREAS, CONCENTRIC RESEARCH CORP. ("Company") and Netscape wish to
                   -------------------------                                 
discuss a proposed business relationship between Netscape and Company.

          NOW, THEREFORE:

          Each party (the "Receiving Party") understands that the other party
(the Disclosing Party") has disclosed or may disclose information (including,
without limitation, computer programs, code, algorithms, names and expertise of
employees and consultants, know-how, formulas, processes, ideas, inventions
(whether patentable or not), schematics and other technical, business, financial
and product development plans, forecasts, strategies and information), which to
the extent previously, presently, or subsequently disclosed to the Receiving
Party is hereinafter referred to as "Proprietary Information" of the Disclosing
Party.  All Proprietary Information disclosed in tangible form by the Disclosing
Party shall be marked "confidential" or "proprietary" and all Proprietary
Information disclosed orally or otherwise in intangible form by the Disclosing
Party shall be designated as "confidential" or "proprietary" at the time of
disclosure and shall be reduced to writing and delivered to the Receiving Party
within thirty (30) days following the date of disclosure.

          In consideration of the parties' discussions and any access the
Receiving Parry may have to Proprietary Information of the Disclosing Party, the
Receiving Party hereby agrees as follows:

          1.  The Receiving Party agrees (i) to hold the Disclosing Party's
Proprietary Information in confidence and to take all necessary precautions to
protect such Proprietary Information (including, without limitation, all
precautions the Receiving Party employs with respect to its own confidential
materials), (ii) not to divulge any such Proprietary Information or any
information derived therefrom to any third person, (iii) not to make any use
whatsoever at any time of such Proprietary Information except to evaluate
internally whether to enter into the currently contemplated business
relationship with the Disclosing Party, (iv) not to remove or export any such
Proprietary Information from the country of the Receiving Party, and (v) not to
copy or reverse engineer, reverse compile or attempt to derive the composition
or underlying information of any such Proprietary Information. The Receiving
Party shall limit the use of and access to the Disclosing Party's Proprietary
Information to the Receiving party's employees who need to know such Proprietary
Information for the purpose of such internal evaluation and shall cause such
employees to comply with the obligations set forth herein. The Receiving Party
shall treat the Proprietary Information with at least the same degree of care
and protection as it would use with respect to its own proprietary information.
The foregoing obligations shall survive for a period of three (3) years from the
date of disclosure of the Proprietary Information. Without granting any right or
license, the Disclosing Party agrees that the foregoing shall not apply
<PAGE>
 
with respect to information the Receiving Party can document (i) is in the
public domain and is readily available at the time of disclosure or which
thereafter enters the public domain and is readily available, through no
improper action or inaction by the Receiving party or any affiliate, agent or
employee, or (ii) was in its possession or known by it prior to receipt from the
Disclosing Party, or (iii) was rightfully disclosed to it by another person
without restriction, or (iv) is independently developed by the Receiving Party
without access to such Proprietary Information, or (v) is required to be
disclosed pursuant to any statutory or regulatory authority, provided the
Disclosing Party is given prompt notice of such requirement and the scope of
such disclosure is limited to the extent possible.

          2.  Immediately upon (i) the decision by either parry not to enter
into a business relationship as contemplated by paragraph 1, or (ii) a request
by the Disclosing Party at any time (which will be effective when actually
received at the Receiving Party's address herein), the Receiving Party will turn
over to the Disclosing Party all Proprietary Information of the Disclosing Party
and all documents or media containing any such Proprietary Information and any
and all copies or extracts thereof.  The Receiving Parry understands that
nothing herein (i) requires the disclosure of any Proprietary Information of the
Disclosing Party, which shall be disclosed if at all solely at the option of the
Disclosing Party, or (n) requires the Disclosing Party to proceed with any
proposed transaction or relationship in connection with which Proprietary
Information may be disclosed.

          3.  Except to the extent required by law, neither party shall disclose
the existence or subject matter of the negotiations or business relationship
contemplated by this Agreement.

          4.  The Receiving Parry acknowledges and agrees that due to the unique
nature of the Disclosing Party's Proprietary Information, there can be no
adequate remedy at law for any breach of its obligations hereunder, that any
such breach may allow the Receiving Party or third parties to unfairly compete
with the Disclosing Party resulting in irreparable harm to the Disclosing Party,
and therefore, that upon any such breach or any threat thereof, the Disclosing
Parry shall be entitled to seek appropriate equitable relief in addition to
whatever remedies it might have at law.  The Receiving Party will notify the
Disclosing Party in writing immediately upon the occurrence of any such
unauthorized release or other breach.  In the event that any of the provisions
of this Agreement shall be held by a court or other tribunal of competent
jurisdiction to be unenforceable, the remaining portions hereof shall remain in
full force and effect.  This Agreement supersedes all prior discussions and
writings with respect to the subject matter hereof, and constitutes the entire
agreement between the parties with respect to the subject matter hereof.  No
waiver or modification of this statement will be binding upon either party
unless made in writing and signed by a duly authorized representative of such
party and no failure or delay in enforcing any right will be deemed a waiver.

                                      -2-
<PAGE>
 
          5.  This Agreement shall be governed by the laws of the State of
California, without regard to conflicts of laws provisions thereof and each
party submits to the jurisdiction and venue of any California State or federal
courts generally serving the Santa Clara county area with respect to the subject
matter of this Agreement.

NETSCAPE COMMUNICATIONS                    CONCENTRIC RESEARCH CORP.
  CORPORATION


By:  /s/ Alan Louie                        By: /s/ Randy Maslow
     -------------------------------           -------------------------------
     Alan Louie                                Randy Maslow

Address:                                   Address:

     501 East Middlefield Road
     Mountain View California 94043

Date: 6/5/95                               Date:
      ------------------------------            ------------------------------

                                      -3-

<PAGE>
 
                                                                   EXHIBIT 10.16


                         Special Customer Arrangement

This MCI Special Customer Arrangement ("Agreement") is made between MCI
Telecommunications Corporations ("MCI") and Sattell Communications LLC
("Customer"), and shall be effective thirty (30) days from the first day of the
next billing cycle following Customer's signature date ("Effective Date").

The rates, discounts and certain other provisions applicable to MCI tariffed
services are set forth in the Contract Tariff.

1.   Authority:  Customer represents and warrants that Customer has the full
     ---------                                                              
right, power and authority to enter into this Agreement, to perform Customer's
obligations hereunder and that the execution, delivery and performance by
Customer of this Agreement will not conflict with or constitute a default under
any contract, agreement or other obligation to which Customer is subject.

2.   Confidential Information:  Each party shall not disclose to any third party
     ------------------------                                                   
during the Term of this Agreement, or during the three (3) year period after
expiration or termination of this Agreement, any of the terms and conditions of
this Agreement unless such disclosure is lawfully required by any federal
governmental agency or is otherwise required to be disclosed by law or is
necessary in any legal proceeding establishing rights and obligations under this
Agreement. Each party reserves the right to terminate this Agreement by giving
written notice to the other party in the event of any unpermitted third party
disclosure hereunder.

3.   Government Law:  This Agreement and all causes of action arising out of the
     --------------                                                             
Agreement, shall be subject to the Communications Act of 1934, as amended (the
"Act"), or, if any part of this Agreement is not covered by the Act, by the
domestic law of the State of Georgia without regard to its choice of law
principles. In the event of a conflict between this Agreement and any subsequent
translations, this English language version shall prevail.

4.   Notices:  All notices, requests, or other communications (excluding
     -------                                                            
invoices) hereunder shall be in writing and hand delivered or addressed and sent
by certified or registered mail, postage prepaid and return receipt requested to
the parties at the address below or such other addresses as may be specified by
written notice. All notices shall be effective when received.

5.   Severability:  All provisions of this Agreement are severable, and the
     ------------                                                          
unenforceability or invalidity of any of the provisions shall not affect the
validity or enforceability of the remaining provisions. The remaining provisions
will be construed in such a manner as to carry out the full intention of the
parties. Section titles or references used in this Agreement shall not have
substantive meaning or context and are not a part of this Agreement.

6.   Entire Agreement:  This Agreement, including the Contract Tariff,
     ----------------                                                 
constitutes the entire agreement between the parties with respect to MCI
Tariffed services and the applicable MCI Tariffs and Tariff Option, and
supersedes all other representations, understandings or agreements which are not
fully expressed herein, whether oral or written. No amendment to this Agreement
shall be valid unless in writing and signed by both parties.

7.   Signature Authorization:  The parties have duly executed and agreed to be
     -----------------------                                                  
bound by this Agreement as evidenced by the signatures of their authorized
representatives above. Each party represents and warrants to the other that the
signatory identified beneath its name above has full authority to execute this
Agreement on its behalf.
<PAGE>
 
8.   Service Provisioning and Receipt:  MCI will provide to Customer interstate
     --------------------------------                                          
and international telecommunications service(s) provided pursuant to the MCI
Tariff FCC No.1, MCI Tariff FCC No. 5, WUI Tariff FCC No.27, and any other
interstate and international tariff of MCI and its affiliates, each as
supplemented by this Agreement, and intrastate telecommunications services
provided pursuant to MCI's state tariffs governing such services ("MCI
Tariffs"). This Agreement incorporates by reference the terms of each such
tariff. MCI may modify its tariffs from time to time in accordance with law and
thereby affect the service(s) furnished to Customer. This is s Specialized
Customer Arrangement as defined in Section B-17.03 of the Tariff.

     MCI will, if required, file a tariff option ("TO") consistent with the
terms of Attachment A, which is fully incorporated herein. In the event a TO
required to implement the terms of this Agreement is suspended or rejected, or
is inconsistent with this Agreement, then Customer may, as its sole remedy,
elect to terminate this Agreement without liability on thirty (30) days' written
notice given not later than thirty (30) days after the event giving rise to the
termination right, unless MCI substantially cures the problem within the notice
period. MCI will use best reasonable commercial efforts to provide Customer with
notice that the TO required to implement this Agreement has been suspended,
rejected, or found to be inconsistent with this Agreement.

     The rates, discounts, terms and conditions of this Agreement, except as set
forth in Attachment A, are those set forth in applicable MCI Tariffs. In the
event of inconsistency between the TO and MCI Tariffs, the TO shall govern. In
the event of inconsistency between this Agreement and applicable MCI Tariffs or
the TO, the TO or applicable MCI Tariffs shall govern. If, where and to the
extend that MCI is no longer required to file Tariffs, MCI will continue to
provide to the Customer MCI services pursuant to the terms and conditions of
this Agreement.



Sattell Communications LLC              MCI Telecommunications Corporation
9145 Deering Avenue                     Three Ravinia Drive
Chatsworth, CA 91311                    Atlanta, GA 30346


/s/ Daniel W. Latham                    /s/ Tom Schilling
- -----------------------------------     -----------------------------------
Authorized Customer Signature           Authorized Signature


Daniel W. Latham                        Tom Schilling, Director
- -----------------------------------     -----------------------------------
Print Name and Title                    Print Name and Title


May 16, 1996                            May 17, 1996
- -----------------------------------     -----------------------------------
Date                                    Date

                                      -2-
<PAGE>
 
                              ATTACHMENT A TO SCA
                                Contract Tariff

This Attachment A to the Agreement contains the rates, terms and conditions of
the MCI services provided under Schedule I.

1.   Term of Service: The term of service is twenty-four (24) months (beginning
     ---------------                                                           
thirty (30) days from the first day of the first billing cycle following the
date of the Customer's execution of this Contract Tariff). Upon completion of
the term of service, the service arrangement under this Agreement shall continue
on a month-to-month basis, and Customer shall receive the rates and discounts
for MCI services as set forth in this Agreement provided, Customer's monthly
usage equals or exceeds one-twelfth of the Annual Minimum.

2.   Description of Service: Service may consist of any one or more standard
     ----------------------                                                 
tariffed MCI services.

3.   Minimum Volume Requirements: For purposes of this Contract Tariff, Base
     ---------------------------                                            
Rates are defined as the rates and discounts for which the Customer qualifies
under this Contract Tariff.

     3.1  Annual Minimum: During each consecutive twelve (12) month period of
          --------------                                                     
the term of service ("Annual Period"), the Customer's use of MCI services under
this Contract Tariff must equal or exceed [*], calculated at Base Rates
("Annual Minimum"). During the thirteenth month of the term of Service, Customer
may upon sixty (60) days prior written notice to MCI, decrease the Annual
Minimum to [*]. The rates and discounts for MCI services will be adjusted as
of the effective date of the notice. Customer may only decrease the Annual
Minimum one time during the term of the service.

4.   Rates and Charges: The Customer will be charged the following rates for
     -----------------                                                      
domestic interstate service usage. (For all domestic intrastate and
international service charge usage, the Customer shall pay standard tariffed
rates set forth in the applicable MCI tariffs.)

     4.1  Postalized Rates: The Customer will be charged the following
          ----------------                                            
postalized rates for the Customer's Interstate usage. [*]

          4.1.1   MCI 800 Service:
                  --------------- 

          (1)  In Lieu of any other rates and discounts, the Customer will be
          charged the following per-minute rates for domestic interstate MCI 800
          DAL usage, depending on termination type and the time of day that the
          call is made:

<TABLE>
<CAPTION>
                Termination Type    Business Day  Non-Business Day
                ------------------  ------------  ----------------
                <S>                 <C>           <C>
                800 DAL             [*]           [*]
                800 CBL             [*]           [*]
</TABLE>


- ---------------------------

    [*]   Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

                                      -3-
<PAGE>
 
          (2)  If the Customer decreases the Annual Minimum to [*] pursuant to
          paragraph 1 above, in lieu of any other rates and discounts, the
          Customer shall be charged the following per-minute rates for domestic
          interstate MCI 800 DAL usage as of the effective date of the decrease,
          depending on the termination type and the time of day that the call is
          made:

<TABLE>
<CAPTION>
                Termination Type    Business Day  Non-Business Day
                ------------------  ------------  ----------------
                <S>                 <C>           <C>
                800 DAL             [*]           [*]
                800 CBL             [*]           [*]
</TABLE>

5.   Volume Discounts: In each Annual Period of the term of service in which the
     ----------------                                                           
Customer satisfies the Annual Minimum, the Customer will be charges the rates
and receive the discounts set forth under the Contract Tariff.

     5.1  MCI HyperStream Frame Relay Service. Pursuant to the Customer's
          ------------------------------------                           
revenue commitments for domestic MCI HyperStream Frame Relay Service, Customer
shall receive with the standard HPP discounts associated with the Monthly
minimum schedule applicable to the two (2) year term of service as set forth in
the Tariff.

     5.2  Charges Not Eligible for Discount: These rates do not apply to the
          ----------------------------------                                
following charges for MCI services other than those described in Section 2; non-
tariffed products; access or egress (or related) charges imposed by third
parties; Directory Assistance charges; standard tariffed non-recurring charges;
taxes or governmental surcharges.

6.   Classifications, Practices and Regulations:
     ------------------------------------------ 

     6.1  Underutilization: If in any Annual Period, the Customer's use of
          -----------------                                               
service under this Contract Tariff, calculated at Base Rates, fails to satisfy
the Annual Minimum, the Customer will be billed and required to pay: (1) all
outstanding amounts billed to the Customer during that Annual Period; and (2) a
underutilization charge (which Customer agrees is reasonable) equal [*].

     6.2  New Technology Change: Customer will not be liable for
          ----------------------                                
underutilization charges where such underutilization charges arise solely as a
result of a provided that in any case Customer shall use its best reasonable
efforts to: (1) direct to MCI new traffic or traffic not currently carried by
MCI in order to meet the Annual Minimum; and (2) certain MCI as the provider of
the service required pursuant to the [*]. In the event Customer's Usage Charges
fall below [*] of the Annual Minimum during the Service Team as the result of a
Customer and MCI shall use good faith efforts to renegotiate the terms and
conditions of the Agreement, including but not limited to all rates and
discounts; provided, however, that if a new agreement is not reached within
sixty (60) days of MCI's notice to Customer

- ------------------------

     [*]  Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.


                                      -4-
<PAGE>
 
that Customer's Usage Charges have fallen below [*] of the Annual Minimum
during the Service Term, MCI may terminate this agreement without liability to
customer, upon ninety (90) days written notice to customer.

     6.3  Business Downturn:  Customer will not be liable for underutilization
          -----------------                                                   
charges where such underutilization charges are solely due to [*]. In the event
the Customer's Usage Charges fall below [*] of the Annual Minimum during the
Service Term as a result of such business downturn, MCI and Customer will
cooperate in efforts to develop a mutually agreeable alternative proposal that
will address the concerns of both parties and comply with all applicable legal
and regulatory requirements and restrictions, provided, however, that if a new
agreement is not reached within thirty (30) days of MCI's notice to Customer
that Customer's Usage Charges have fallen below [*] of the Annual Minimum, MCI
may terminate this Agreement without liability to Customer upon ninety (90) days
written notice. By way of example and not limitation, the alternative proposal
may include changes in discounts, credits, revenue and/or volume commitments,
the multi-year service period, and other provisions. Subject to all applicable
legal and regulatory requirements of the Federal Communications Commission and
the Communications Act of 1934, MCI will prepare and file any tariff revisions
necessary to implement such mutually agreeable alternative proposal. This
provision shall not apply to a change resulting from a decision by a Customer
to: (1) reduce its overall use of telecommunications service; (2) alter its
telecommunications network architecture; or (3) transfer portions of its
telecommunications traffic or projected growth to carriers other than MCI. This
provision shall also not apply during the first twelve (12) months of the
Service Term and, after the first twelve (12) months, may only be used one (1)
time by Customer during the Service Term. Customer must give MCI immediate
written notice of the conditions it believes will require the application of
this provision.

     6.4  Force Majeure: Customer will not be liable for the underutilization
          --------------                                                     
charges where such underutilization are solely due to events beyond the
reasonable control of the customer. The Customer shall promptly notify MCI of
the force majeure circumstances, and the Service Team shall be extended by the
time of the deal caused by the force majeure event.

     6.5  Termination:
          ----------- 

          6.5.1.    Except as set forth below, if the Customer terminates
          service under the Contract Tariff after the Effective Date and before
          the expiration of the term of service, it will constitute a breach of
          this Contract Tariff and Customer will be billed and required to: [*]



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with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

                                      -5-
<PAGE>
 
          6.5.2.    The Customer may terminate this Contract prior to the
          expiration of the term of service without termination liability if
          Customer enters into another Contract Tariff with term and volume
          commitments equal to or greater than the commitments under this
          Contract Tariff.

          6.5.3.    If the Customer becomes dissatisfied with the agreement or
          the MCI services or with MCI's performance in connection with the
          provision of MCI services under this Agreement within thirty (30) days
          of the Effective Date, Customer terminates this Agreement pursuant to
          this paragraph 6.5.3, MCI will release to Customer the surety provided
          in paragraph 6.7 below, less the amount of Customer's unpaid Usage
          Charges up to the time of such termination.

     6.6  Service Interruptions
          ---------------------

          6.6.1.    Customer shall be entitled to Credit Allowances for Service
          Interruptions in accordance with Section B.15 of the Tariff. A Service
          Interruption begins when Customer reports the interruption to MCI and
          releases the "Service Element" (as hereinafter defined) for testing
          and repair ad ends when MCI retenders the Service Element to Customer.
          For the purpose of determining the Annual Minimum, MCI will not reduce
          Usage Charges by the amount of Credit Allowances applied. For purposes
          of this Agreement, "Service Element" refers to the specific MCI
          service affected at the specific geographic Customer location
          affected.

          6.6.2.    Customer may discontinue receipt of service on a Service
          Element at any time without liability except as otherwise expressly
          provided for in the Tariff or this Agreement (an example of such a
          provision might be where a private line installation charge is waived
          but is to be assessed if the line is not in place for a minimum
          period). If Customer discontinues receipt of service on a Service
          Element having chronic Service Interruptions and does not take
          substitute service form MCI, the Annual Minimum for purposes of
          assessing underutilization charges shall be reduced by the average
          monthly Usage Charges for the discontinued Service Element measured
          over the last three (3) billing months prior to discontinuation. A
          Service Element with chronic Service Interruptions is one on which
          there have been three or more Service Interruptions, each consisting
          of thirty (30) or more minutes, totaling twenty-four (24) or more
          hours within three (3) consecutive calendar months.

     6.7  Payment Arrangements: The Customer is required to pay MCI for its
          --------------------                                             
services within thirty (30) days of the Customer's receipt of MCI's invoice. In
consideration for services provided by MCI, Customer agrees to pay surety in the
amount of [*]. Surety shall be provided by June 3, 1996. Initial surety
requirements shall be based on estimated usage projections and MCI shall reserve
the right to require additional surety based on MCI traffic reporting and/or
actual usage. Should the customer fail to provide additional surety, MCI may
elect to disconnect all services immediately and without further notice. Surety
may be in the form of a cash deposit, an Irrevocable

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with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

                                      -6-
<PAGE>
 
Letter of Credit for a term of one year issued by am MCI approved financial
institution of a Cross Corporate Guarantee from Diana Corporation. If Customer
elects to provide the Cross Corporate Guarantee, MCI will release the surety
upon receipt of such Guarantee. Cash deposits will be retained in an interest
bearing account held by MCI for a minimum of twelve (12) months. MCI shall
reserve the right to determine the customer's eligibility for refund of the
deposit based on customer's payment history and financial solvency and to retain
such deposit as is required to limit MCI's exposure.

     6.8  Tariffed Rates: If MCI offers discounts applicable to a combination of
          ---------------                                                       
its services (as opposed to discounts on an individual service), the Customer
who has subscribed to one of the combined services may elect to receive the
benefits of such discounts in lieu of its SCA discounts. If the Customer so
chooses, the new discounts become binding for the remainder of the terms of
service.

     6.9  Conditions: In order for Customer to be eligible to receive the rates
          -----------                                                          
and discounts provided under this Agreement, Customer must satisfy the following
conditions on an annual basis:

          6.9.1.    Customer agrees that it will utilize MCI [*] of Customer's
          domestic interstate dedicated 800 traffic during the Service Term (the
          Exclusive Carrier Requirement").

          6.9.2.    MCI may request in writing and Customer will promptly
          provide to MCI in writing, proof satisfactory to MCI that Customer is
          satisfying the terms of the Exclusive Carrier Requirement for any
          Annual Period ("Documentation"). MCI may review the Documentation
          solely for the purpose of determining Customer's compliance with the
          Exclusive Carrier Requirement.

          6.9.3.    The rates and discounts for MCI Services set forth in this
          Agreement are conditioned upon Customer's satisfaction of the
          Exclusive Carrier Requirement. If Customer fails to satisfy the
          Exclusive Carrier Requirements during any Annual Period, then the
          rates and discounts which shall be applied to Customer's usage of MCI
          Services for such Annual Period shall be MCI standard Tariff rates
          (less standard discounts) notwithstanding anything to the contrary in
          the Agreement.

          6.9.4.    If the percentage of Customer's usage of MCI 800 Service
          terminating via dedicated access facilities during any annual billing
          period (excluding usage routed to switched lines for disaster recovery
          purposes only) is less [*] of its total usage of MCI 800 Service (as
          measured in minutes of use), Customer will pay an additional [*] per
          minute of usage of MCI 800 Service terminating via dedicated access
          facilities below such [*] threshold.

          6.9.5.    If the percentage of Customer's usage of interstate MCI 800
          Service is less than eighty percent (80%) of its total usage of MCI
          800 Service (as measured in minutes of use), Customer will pay an
          additional [*] per minute of usage of interstate MCI 800 Service
          under such eighty percent (80%) threshold.

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with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

                                      -7-
<PAGE>
 
           6.9.6.    If the percentage of Customer's usage of MCI 800 Service
           occurring during the Non-Business Day time period is less than sixty
           percent (60%) of its total usage of MCI 800 Service, Customer will
           pay an additional [*] per minute of usage of Non-Business Day MCI
           800 Service under such sixty percent (60%) threshold.

     6.10  Credits:
           ------- 

           6.10.1.   The Customer will receive a credit, not to exceed [*],
           for the one-time charges associated with the implementation of MCI
           service under this Contract Tariff. Such credits will be issued from
           time to time throughout the term of office as MCI service under this
           Contract Tariff is installed. Any applicable Tariffed promotional
           credits will be applied prior to this credit.

           6.10.2.   If the Customer decreases the Annual Minimum to [*]
           pursuant to paragraph 1 above, for each consecutive three (3) month
           period following the effective date of the decrease (each a Quarterly
           Period"), Customer shall receive a credit of ten percent (10%)
           calculated and applied to the [*] of the Customer's total domestic
           interstate MCI 800 DAL Usage Charges for each Quarterly Period.

7.   This agreement shall be binding upon and inure to the benefit of the
successors and permitted assigns of the parties hereto. Neither this agreement,
nor any rights or obligations of Customer herein shall be transferable or
assignable by Customer without MCI's prior written consent, which consent shall
not be reasonable withheld.

8.   Service under this option is available to Customers ordering service within
30 days of the Effective Date of this option.











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requested with respect to the omitted portions.

                                      -8-
<PAGE>
 
                                FIRST AMENDMENT
                      TO MCI SPECIAL CUSTOMER ARRANGEMENT


     This is the first amendment (the "Amendment") to the MCI Special Customer
Arrangement between MCI Telecommunications Corporation ("MCI") and Sattell
Communications LLC ("Customer"), which was signed by Customer on May 16, 1996
(the "Original Agreement"). This Amendment is effective as of thirty (30) days
after the first day of the next full month's billing cycle following the
Customer signature date ("Amendment Effective Date").

1.   Survival of Original Agreement.  Except as otherwise expressly modified or
     ------------------------------                                            
     amended herein, all terms and conditions contained in the Original
     Agreement shall remain in full force and effect and shall not be altered or
     changed by this Amendment. The Original Agreement including this Amendment
     shall be referred to as the "Agreement".

2.   Effective Date.  The opening paragraph of the Original Agreement shall be
     --------------                                                           
     deleted in its entirety and restated as follows:

          "This MCI Special Customer Arrangement ("Agreement") is made between
          MCI Telecommunications Corporation ("MCI") and Sattell Communications
          LLC ("Customer") and shall be effective as of June 7, 1996 ("SCA
          Effective Date")."

3.   Add New Paragraph 4.1.1(3).  A new paragraph 4.1.1(3) is hereby added and
     --------------------------                                               
     incorporated into Attachment A of the Original Agreement as follows:

          "This is a featureless product offering. Customer will incur
          additional charges for any features ordered."

4.   Add New Paragraph 4.1.2.  A new paragraph 4.1.2 is hereby added and
     -----------------------                                            
     incorporated into Attachment A of the Original Agreement as follows:

          "4.1.2  MCI Vision Service:
                  ------------------ 

          (1) Except as set forth in paragraph 4.1.2 (2) below, for domestic MCI
          Vision Service, Customer will pay the standard rates pursuant to the
          Vision Power Rate Program as set forth in the Tariff and receive the
          discounts associated with the MCI Vision Power Rate Value Insurance
          Plan Two (2) year and [*] commitment levels as set forth in the
          Tariff except that minimum term and volume levels shall not apply.


- ---------------------

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requested with respect to the omitted portions.

<PAGE>
 
     (2)  In lieu of the discounts set forth in paragraph 4.1.2(1) above, for
     interstate MCI Vision Service, Customer shall pay the following postalized
     rates depending on the type of access and the time of day that the call
     occurs.

<TABLE>
<CAPTION>
 
                  Access            Peak         Off-Peak
                ----------        --------      ----------
                <S>               <C>           <C>
                Dedicated           [*]          [*]
                Switched            [*]          [*]
</TABLE>

5.   Paragraph 5.1 Modification.  Paragraph 5.1 of Attachment A to the Original
     --------------------------                                                
     Agreement shall be deleted in its entirety and restated as follows:

          "5.1  MCI HyperStream Frame Relay Service. Pursuant to the Customer's
                -----------------------------------
          revenue commitments for domestic MCI HyperStream Frame Relay Service,
          Customer shall receive with the standard HPP discount associated with
          a [*] Monthly Minimum and two (2) year term of service as set forth
          in the Tariff."

6.   Paragraph 6.5.3 Modification.  Paragraph 6.5.3 of Attachment A to the
     ----------------------------                                         
     Original Agreement shall be deleted in its entirety and restated as
     follows: 

          "6.5.3 If the Customer becomes dissatisfied with this Agreement within
          forty (40) days of the Effective Date, Customer may terminate this
          Agreement without termination liability. If Customer terminates this
          Agreement pursuant to this paragraph 6.5.3, MCI will release to
          Customer the surety provided in paragraph 6.7 below, less the amount
          of Customer's unpaid Usage Charges up to the time of such
          termination."

7.   Paragraph 6.7 Modification.  Paragraph 6.7 of Attachment A to the Original
     --------------------------                                                
     Agreement shall be deleted in its entirety and restated as follows:

          "6.7  Payment Arrangements: The Customer is required to pay MCI for
                --------------------
          its services within thirty (30) days of the Customer's receipt of
          MCI's invoice. In consideration for services provided by MCI, customer
          agrees to pay surety in the amount of [*]. Surety shall be provided
          by June 3, 1996. Initial surety requirements shall be based on
          estimated usage projections and MCI shall reserve the right to require
          additional surety based on MCI traffic reporting and/or actual usage.
          Should the customer fail to provide additional surety in a form
          acceptable to MCI within ten (10) business days after Customer's
          notice of such requirement, MCI may elect to disconnect all services
          immediately and without further notice. Surety may be in the form of a
          cash deposit, an Irrevocable Letter of Credit for a term of one year
          issued by an MCI approved financial institution, a

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requested with respect to the omitted portions.

                                      -2-
<PAGE>
 
          performance bond with terms and conditions and from an issuer
          acceptable to MCI or a cross corporate guarantee from Diana
          Corporation. If Customer elects to provide the cross corporate
          guarantee; MCI will release other forms of surety upon receipt of such
          cross corporate guarantee. However, should Customer elect to terminate
          the cross corporate guarantee currently in effect under this
          Agreement, Customer must provide alternative surety acceptable to MCI
          concurrently with such termination of the cross corporate guarantee.
          Cash deposits will be retained in an interest bearing account held by
          MCI for a minimum of twelve (12) months. MCI shall reserve the right
          to determine the customer's eligibility for refund of the deposit
          based on customer's payment history and financial solvency and to
          retain such deposit as is required to limit MCI's exposure."

     Once this Agreement has been fully executed, any further amendments must be
in writing and signed by both parties.


Accepted and agreed:

Sattell Communications LLC              MCI Telecommunications Corporations



By:  /s/ James Fiedler                  By: /s/ Tom Schilling
     --------------------------            ----------------------------

Name: James Fiedler                     Name: Tom Schilling
     --------------------------              --------------------------

Title: Chairman & CEO                   Title: Director
      -------------------------               -------------------------

Date: 7/1/96                            Date: 7/2/96
     --------------------------              --------------------------

                                      -3-
<PAGE>
 
                               SECOND AMENDMENT
                      TO MCI SPECIAL CUSTOMER ARRANGEMENT


     This is the Second Amendment (this "Amendment") to MCI Special Customer
Arrangement by and between MCI Telecommunications Corporation ("MCI") and
Concentric Network Corporation ("Customer") and amends that certain MCI Special
Customer Arrangement between MCI and Sattel Communications L.L.C. ("Sattel")
which was effective as of June 7, 1996 (the "SCA") and amended by that certain
First Amendment to MCI Special Customer which was signed by Sattel on July 1,
1996 (the "First Amendment").  The SCA and the First Amendment shall
collectively be referred to as the "Original Agreement."  The Original Agreement
was assigned to Customer by Sattel pursuant to an Assignment and Novation
Agreement entered into as of August 7, 1996.  Unless otherwise defined herein,
capitalized terms used in this Amendment shall have the same meanings as set
forth in the Original Agreement.

     The parties hereby agree that the Original Agreement is amended as follows:

1.   Survival of Original Agreement.  Except as otherwise expressly modified or
     ------------------------------                                            
     amended herein, all terms and conditions contained in the Original
     Agreement shall remain in full force and effect and shall not be altered or
     changed by this Amendment. The Original Agreement and this Amendment shall
     collectively be referred to as the "Agreement."

2.   Effective Date.  This Amendment is effective as of November 1, 1996.
     --------------                                                      

3.   Revised Attachment A to SCA.  Attachment A of the Original Agreement shall
     ---------------------------                                               
     be deleted in its entirety and replaced by the revised Attachment A
     attached to, and incorporated by reference into, this Amendment.

4.   Complete Agreement.  The Agreement, together with MCI's F.C.C. Tariffs No.
     ------------------                                                        
     1 and 8, as amended from time to time, constitutes the complete agreement
     of the parties and supersedes all other prior agreements and
     representations concerning its subject matter.

     This offer shall remain open and be capable of being accepted by Customer
until October 24, 1996.  Once this Amendment has been fully executed, any
further amendments must be in writing and signed by both parties.
<PAGE>
 
Accepted and agreed:


MCI Telecommunications Corporation              Concentric Network Corporation



By: /s/ Edward W. Smith                         By: /s/ John Peters
   --------------------------------                -----------------------------

Name: Edward W. Smith                           Name: John Peters
     ------------------------------                  ---------------------------

Title: Director                                 Title: Exec VP
      -----------------------------                   --------------------------

Date:  11/1/96                                  Date: 10/17/96
     ------------------------------                  ---------------------------
<PAGE>
 
                              ATTACHMENT A TO SCA
                                Contract Tariff


     This Attachment A to the Agreement contains the rates, discounts, terms and
conditions of the MCI services provided under Schedule I.

1.   Term of Service.  The term of service is twenty-four (24) months from June
     ---------------                                                           
     7, 1996 (the "Effective Date"). Upon completion of the term of service, the
     service arrangement under this Agreement will continue on a month-to-month
     basis, and Customer will receive the rates and discounts for MCI services
     as set forth in this Agreement provided, Customer's monthly usage equals or
     exceeds one-twelfth (1/12th) of the Second Minimum, as that term is defined
     in Section 3 below.

2.   Description of Service.  Service may consist of any one or more standard
     ----------------------                                                  
     tariffed MCI services.

3.   Minimum Volume Requirements.  For purposes of this Contract Tariff, Base
     ---------------------------                                             
     Rates are defined as the rates and discounts for which Customer qualifies
     under this Contract Tariff.

     3.1  Customer's Minimums.  From the Effective Date through April 30, 1997
          -------------------                                                 
          (the "First Period"), Customer's use of MCI services under this
          Contract Tariff must equal or exceed Three million six hundred
          thousand dollars ($3,600,000), calculated at Base Rates (the "First
          Minimum"). From May 1, 1997 through June 6,1998 (the "Second Period").
          Customer's use of MCI services under this Contract Tariff must equal
          or exceed Four million nine hundred fifteen thousand dollars
          ($4,915,000), calculated at Base Rates (the "Second Minimum"). Any
          time after July 1, 1997, Customer may, upon sixty (60) days prior
          written notice to MCI, decrease the Second Minimum to Three million
          six hundred thousand dollars ($3,600,000). The rates and discounts
          for MCI services will be adjusted as of the effective date of such
          notice. Customer may only decrease the Second Minimum one time during
          the term of the service.

     3.2  Data Sub-Minimum.  During the First and Second Periods combined,
          ----------------                                                
          Customer's use of MCI Dedicated Leased Line Services under this
          Contract Tariff must equal or exceed [*], calculated at Base Rates
          (the "Data Sub-Minimum"). Customer usage of MCI Dedicated Leased Line
          Services will be eligible to count towards each of the First and
          Second Minimums and the Data Sub-Minimum.


- -------------------------
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with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.
<PAGE>
 
4.   Rates and Charges.  The Customer will be charged the following rates for
     -----------------                                                       
     domestic interstate service usage. (For all domestic intrastate and
     international service usage, Customer will pay standard tariffed rates set
     forth in the applicable MCI tariffs.)

     4.1  Postalized Rates.  The Customer will be charged the following 
          ----------------                                             
     postalized rates for Customer's interstate usage. [*]          

          4.1.1     MCI 800 Service:
                    --------------- 

                    (1)  In lieu of any other rates and discounts, Customer will
                         be charged the following per-minute rates for domestic
                         interstate MCI 800 DAL usage, depending on termination
                         type and the time of day that the call is made:

<TABLE> 
<CAPTION> 
 
                         Termination Type        Business Day   Non-Business Day
                         ----------------        -------------  ----------------
                         <S>                     <C>            <C>
                         800 DAL                  [*]            [*]
                         800 CBL                  [*]            [*]
</TABLE>


                    (2)  If Customer decreases the Second Minimum to Three
                         Million Six Hundred Thousand Dollars ($3,600,000)
                         pursuant to Section 3.1 above, in lieu of any other
                         rates and discounts, Customer will be charged the
                         following per-minute rates for domestic interstate MCI
                         800 DAL usage as of the effective date of the decrease,
                         depending on the termination type and the time of day
                         that the call is made:

<TABLE>
<CAPTION>
 
                         Termination Type        Business Day  Non-Business Day
                         ----------------        ------------  ----------------
                         <S>                     <C>           <C>
                         800 DAL                  [*]           [*] 
                         800 CBL                  [*]           [*]
</TABLE>

                    (3)  This is a featureless product offering. Customer will
                         incur additional charges for any features ordered.


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requested with respect to the omitted portions.


                                      -2-
<PAGE>
 
          4.1.2     MCI Vision Service:
                    ------------------

                    (1)  Except as set forth in paragraph 4.1.2(2) below, for
                         domestic MCI Vision Service, Customer will pay the
                         standard rates pursuant to the Vision Power Rate
                         Program as set forth in the Tariff and receive the
                         discounts associated with the MCI Vision Power Rate
                         Value Insurance Plan Two (2) year and [*] commitment
                         levels as set forth in the Tariff except that minimum
                         term and volume levels will not apply.

                    (2)  In lieu of the discounts set forth in paragraph
                         4.1.2(l) above, for interstate MCI Vision Service,
                         Customer will pay the following postalized rates
                         depending on the type of access and the time of day
                         that the call occurs.

<TABLE>
<CAPTION>
 
                          Access              Peak             Off-Peak
                         ---------          ---------         ----------
                         <S>                <C>               <C>
                         Dedicated             [*]                [*] 
                         Switched              [*]                [*]
</TABLE>

          4.1.3     Dedicated Leased Line Services:
                    ------------------------------ 

                    (1)  In lieu of any other rates and discounts and except as
                         set forth in paragraph 4.1.3(2) below, Customer will be
                         charged the following per mile rates for domestic
                         interstate Inter Office Channel ("OC") Services over
                         MCI Dedicated Leased Line Services:

                         Terrestrial Digital Service 1.5 ("TDS 1.5"):
                         ------------------------------------------- 

                         Miles*               Monthly Rate

                           [*]                     [*]
                           [*]                     [*]
                           [*]                     [*]
                           [*]                     [*]


- -------------------------
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with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.

                                      -3-
<PAGE>
 
                         Terrestrial Digital Service 45 ("TDS 45"):
                         ----------------------------------------- 

                         Miles*               Monthly Rate

                         [*]                  [*]
                         [*]                  [*]
                         [*]                  [*]
                         [*]                  [*]

                         * Miles are not calculated on an incremental basis, for
                           example, [*]

                    (2)  Customer shall receive the discounts associated with
                         the three (3)-year Access Pricing Plan as set forth in
                         the Tariff on Customer's Dedicated Leased Line Service
                         usage. The standard term and volume commitments set
                         forth in the Tariff shall apply. To the extent that
                         Customer has its circuits located at MCI facilities or
                         locations, or has otherwise provided for local access,
                         Customer will not be obligated to pay Access
                         Collocation and/or Central Office Connection charges as
                         set forth in the Tariff.

5.   Volume Discounts.  Except as set forth in Sections 3.1 and 4.1.2 above, if
     ----------------                                                          
     Customer satisfies the First and Second Minimums, Customer will be charged
     the rates and receive the discounts set forth under this Section 5.

     5.1  MCI HyperStream Frame Relay Service.  For domestic MCI HyperStream
          -----------------------------------                               
          Frame Relay Service, Customer will receive with the standard E{PP
          discount associated with a [*] Monthly Minimum and two (2) year term
          of service as set forth in the Tariff. This discount does not apply to
          the following: charges for MCI services other than those described in
          Section 2, non-tariffed products, access or egress (or related)
          charges imposed by third parties; Directory Assistance charges;
          standard tariffed non-recurring charges; taxes or governmental
          surcharges.

6.   Classifications, Practices, and Regulations.
     ------------------------------------------- 

     6.1  Underutilization.  If in either the First or Second Period, Customer's
          ----------------                                                      
          use of service under this Contract Tariff, calculated at Base Rates,
          fails to satisfy the respective First or Second Minimum, Customer will
          be billed and required to pay: (1) all 


- -------------------------
     [*]Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.

                                      -4-
<PAGE>
 
          outstanding amounts billed to Customer during the applicable First
          and/or Second Period; and, (2) an underutilization charge (which
          Customer agrees is reasonable) equal to [*]

     6.2  New Technology Change.  Customer will not be liable for 
          ---------------------                                  
          underutilization charges where such underutilization charges arise
          solely [*] provided that in any case Customer will use its best
          reasonable efforts to: (1) direct to MCI new traffic or traffic not
          currently carried by MCI in order to meet the First and/or Second
          Minimum; and (2) retain MCI as the provider of the service required
          pursuant to the New Technology Change. [*] In the event Customer's
          Usage Charges fall below seventy percent (70%) of the First and/or
          Second Minimum during the term of service as the result of a [*],
          Customer and MCI will use good faith efforts to re-negotiate the terms
          and conditions of this Agreement, including but not limited to all
          rates and discounts; provided however, that if a new agreement is not
          reached within sixty (60) days of MCI's notice to Customer that
          Customer's Usage Charges have fallen below seventy percent (70%) of
          the First and/or Second Minimum during the term of service, MCI may
          terminate this Agreement without liability to Customer upon ninety
          (90) days prior written notice to Customer.

     6.3  Business Downturn.  Customer will not be liable for underutilization
          -----------------                                                   
          charges where such underutilization charges are solely [*]. In the
          event that Customer's Usage Charges fall below seventy percent (70%)
          of the First and or Second Minimum during the term of service as a
          result of such business downturn, MCI and Customer will cooperate in
          efforts to develop a mutually agreeable alternative proposal that will
          address the concerns of both parties and comply with all applicable
          legal and

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                                      -5-

<PAGE>
 
          regulatory requirements and restrictions, provided, however, that if a
          new agreement is not reached within thirty (30) days of MCI's notice
          to Customer that Customer's Usage Charges have fallen below [*], MCI
          may terminate this Agreement without liability to Customer upon ninety
          (90) days written notice. By way of example and not limitation, the
          alternative proposal may include changes in discounts, credits,
          revenue, and/or volume commitments, the multi-year service period, and
          other provisions. Subject to all applicable legal and regulatory
          requirements of the Federal Communications Commission and the
          Communications Act of 1934, as amended, MCI will prepare and file any
          tariff revisions necessary to implement such mutually agreeable
          alternative proposal. This provision will not apply to a change
          resulting from a decision by Customer to: (1) reduce its overall use
          of telecommunications service; (2) alter its telecommunications
          network architecture; or (3) transfer portions of its
          telecommunications traffic or projected growth to carriers other than
          MCI. This provision will also not apply during the first twelve (12)
          months of the term of service and, after the first twelve (12) months,
          may only be used one (1) time by Customer during the term of service.
          Customer must give MCI immediate written notice of the conditions it
          believes will require the application of this provision.

     6.4  Force Majeure.  Customer will not be liable for underutilization
          -------------                                                   
          charges where such underutilization charges are solely due to events
          beyond the reasonable control of Customer. The Customer will promptly
          notify MCI of the force majeure circumstances, and the term of service
          will be extended by the time of the delay caused by the force majeure
          event.

     6.5  Termination.
          ----------- 

          6.5.1     Except as set forth below, if Customer terminates service
                    under this Contract Tariff after the Effective Date and
                    before the expiration of the term of service, it will
                    constitute a breach of this Contract Tariff and Customer
                    will be billed and required to: (1) repay a pro rata portion
                    of all credits received under this Contract Tariff; and, (2)
                    pay an early termination charge equal to one hundred percent
                    (100%) of the First and/or Second Minimum for the First
                    and/or Second Period remaining in the term of service or a
                    pro rata portion thereof for any partial First and/or Second
                    Period.


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                                      -6-
<PAGE>
 
          6.5.2     The Customer may terminate this Contract Tariff prior to the
                    expiration of the term of service without termination
                    liability if Customer enters into another Contract Tariff
                    with term and volume commitments equal to or greater than
                    the commitments under this Contract Tariff.

     6.6  Service Interruptions.
          --------------------- 

          6.6.1     Customer will be entitled to Credit Allowances for Service
                    Interruptions in accordance with Section 6.15 of the Tariff.
                    A Service Interruption begins when Customer reports the
                    interruption to MCI and releases the "Service Element" (as
                    hereinafter defined) for testing and repair and ends when
                    MCI retenders the Service Element to Customer. For the
                    purpose of determining the First and/or Second Minimum, MCI
                    will not reduce Usage Charges by the amount of Credit
                    Allowances applied. For purposes of this Agreement, "Service
                    Element" refers to the specific MCI service affected at the
                    specific geographic Customer location affected.

          6.6.2     Customer may discontinue receipt of service on a Service
                    Element at any time without liability except as otherwise
                    expressly provided for in the Tariff or this Agreement (an
                    example of such a provision might be where a private line
                    installation charge is waived but is to be assessed if the
                    line is not in place for a minimum period). If Customer
                    discontinues receipt of service on a "Service Element having
                    chronic Service Interruptions" and does not take substitute
                    service from MCI, the First and/or Second Minimum for
                    purposes of assessing underutilization charges will be
                    reduced by the average monthly Usage Charges for the
                    discontinued Service Element measured over the last three
                    (3) billing months prior to discontinuation. For purposes of
                    this Contract Tariff, a Service Element having chronic
                    Service Interruptions is one on which there have been three
                    (3) or more Service Interruptions, each consisting of thirty
                    (30) or more minutes, totaling twenty-four (24) or more
                    hours within three (3) consecutive calendar months.

     6.7  Payment Arrangements.  The Customer is required to pay MCI for its
          --------------------                                              
          services within (30) days of the date of MCI's invoice. In
          consideration for services provided by MCI, Customer agrees to pay
          surety in the amount of [*]. Initial surety requirements will be based
          on estimated usage projections and MCI will reserve the right to
          require additional surety based on MCI traffic reporting and/or actual
          usage. Should Customer fail to provide additional surety in a form
          acceptable to MCI within 


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                                      -7-
<PAGE>
 
          ten (10) business days after Customer's notice of such requirement,
          MCI may elect to disconnect all services immediately and without
          further notice. Surety may be in the form of a cash deposit, an
          Irrevocable Letter of Credit for a term of one (1) year issued by an
          MCI approved financial institution, a performance bond with terms and
          conditions and from an insurer acceptable to MCI or a cross corporate
          guarantee from Diana Corporation. If Customer elects to provide the
          cross corporate guarantee, MCI will release other forms of surety upon
          receipt of such cross corporate guarantee. However, should Customer
          elect to terminate the cross corporate guarantee currently in effect
          under this Agreement, Customer must provide alternative surety
          acceptable to MCI concurrently with such termination of the cross
          corporate guarantee. Cash deposits will be retained in an interest
          bearing account held by MCI for a minimum of twelve (12) months. MCI
          will reserve the right to determine Customer's eligibility for refund
          of the deposit based on Customer's payment history and financial
          solvency and to retain such deposit as is required to limit MCI's
          exposure.

     6.8  Tariffed Rates.  If MCI offers discounts applicable to a combination
          --------------                                                      
          of its services (as opposed to discounts on an individual service),
          Customer who has subscribed to one of the combined services may elect
          to receive the benefits of such discounts in lieu of its SCA
          discounts. If Customer so chooses, the new discounts become binding
          for the remainder of the term of service.

     6.9  Conditions.  In order for Customer to be eligible to receive the rates
          ----------                                                            
          and discounts provided under this Agreement, Customer must satisfy the
          following conditions on an annual basis:

          6.9.1     Customer agrees that it will utilize MCI [*] during the term
                    of service (the "Exclusive Carrier Requirement").

          6.9.2     MCI may request in writing and Customer will promptly
                    provide to MCI in writing, proof satisfactory to MCI that
                    Customer is satisfying the terms of the Exclusive Carrier
                    Requirement for the First and/or Second Period
                    ("Documentation"). MCI may review the Documentation solely
                    for the purpose of determining Customer's compliance with
                    the Exclusive Carrier Requirement.

          6.9.3     The rates and discounts for MCI Services set forth in this
                    Agreement are conditioned upon Customers satisfaction of the
                    Exclusive Carrier Requirement. If Customer fails to satisfy
                    the Exclusive Carrier Requirement 


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                                      -8-
<PAGE>
 
                    be applied to Customer's usage of MCI Services for the First
                    and/or Second Period will be MCI standard Tariff rates (less
                    standard discounts) notwithstanding anything to the contrary
                    in this Agreement.

          6.9.4     If the percentage of Customer's usage of MCI 800 Service
                    terminating via dedicated access facilities during any
                    annual billing period (excluding usage routed to switched
                    lines for disaster recovery purposes only) is less than one
                    hundred percent (100%) of its total usage of MCI 800 Service
                    (as measured in minutes of use), Customer will pay an
                    additional [*] per minute of usage of MCI 800 Service
                    terminating via dedicated access facilities below such one
                    hundred percent (100%) threshold.

          6.9.5     If the percentage of Customer's usage of interstate MCI 800
                    Service is less than eighty percent (80%) of its total usage
                    of MCI 800 Service (as measured in minutes of use), Customer
                    will pay an additional [*] per minute of usage of
                    interstate MCI 800 Service under such eighty percent (80%)
                    threshold.

          6.9.6     If the percentage of Customer's usage of MCI 800 Service
                    occurring during the Non-Business Day time period is less
                    than sixty percent (60%) of its total usage of MCI 800
                    Service, Customer will pay an additional [*] per minute of
                    usage of Non-Business Day MCI 800 Service under such sixty
                    percent (60%) threshold.

          6.9.7     Customer represents that as of April 30, 1997, Customer's
                    total of all IOC mileage for leased TDS 1.5 circuits will be
                    equal to an average of [*] miles or less and as of October
                    31, 1997, TDS 45 circuits will be equal to an average of [*]
                    miles or less.

          6.9.8     Customer represents that as of April 30, 1997, Customer will
                    lease from MCI a minimum of [*] TDS 1.5 circuits and as of
                    October 31, 1997, a minimum of [*] TDS 45 circuits;
                    provided, however, that such TDS 1.5 and 45 circuits are
                    available to Customer's selected locations.

     6.10 Credits.
          ------- 

          6.10.1    The Customer will receive a credit, not to exceed [*], for
                    the one-time charges associated with the implementation of
                    MCI service under this Contract Tariff. Such credits will be
                    issued from time to time throughout the


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                                      -9-
<PAGE>
 
                    Contract Tariff. Such credits will be issued from time to
                    time throughout the term of service as MCI service under
                    this Contract Tariff is installed. Any applicable Tariffed
                    promotional credits will be applied prior to this credit.

          6.10.2    If Customer decreases the Second Minimum to [*] pursuant to
                    Section 3.1 above, for each consecutive three (3) month
                    period following the effective date of the decrease (each a
                    "Quarterly Period"). Customer will receive a credit of [*]
                    calculated on and applied to the first [*] of Customer's
                    total domestic interstate MCI 800 DAL Usage Charges for each
                    Quarterly Period.

          6.10.3    If from the Effective Date until November 30, 1996,
                    Customer's usage of MCI 800 Service intrastate equals or
                    exceeds the one (1) of the total 800 intrastate minute
                    levels set forth below, then Customer will receive one (1)
                    of the corresponding credits set forth below on Customer's
                    domestic interstate usage charges
<TABLE> 
<CAPTION> 
                    Total 800 Intrastate Minutes                    Credit
                    ----------------------------                  ----------
                    <S>                                           <C> 
                           [*]                                      [*]
                           [*]                                      [*]
</TABLE> 
                    Customer is entitled to only one (1) of the above credits
                    and any such credit to which Customer is entitled to will be
                    applied to Customer's December 1996 monthly invoice

7.   Assignment.  This Agreement will be binding upon and inure to the benefit
     ----------                                                               
     of the successors and permitted assigns of the parties hereto. Neither this
     Agreement, nor any rights or obligations of Customer herein will be
     transferable or assignable by Customer without MCI's prior written consent,
     which consent will not be unreasonably withheld.

8.   Ordered Service.  Service under this option is available to other customers
     ---------------                                                            
     MCI ordering service within 30 days of the Effective Date of this option.


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                                     -10-
<PAGE>
 
                       ASSIGNMENT AND NOVATION AGREEMENT


This Assignment and Novation Agreement (the "Agreement") is made and entered
into as of August 7, 1996 (the "Effective Date"), by and between MCI
Telecommunications Corporation ("MCI"), Sattel Communications L.L.C. with
offices located at 9145 Deering Avenue, Chatsworth, California 91311 ("Sattel")
and Concentric Network Corporation with offices located at 10590 N. Tantau
Avenue, Cupertino, California 95014 ("CNC").

1.   The parties stipulate and recite that:

     a.   MCI and Sattel entered into an MCI Special Customer Arrangement, dated
          May 17, which was amended by the First Amendment, dated July 2, 1996
          (the "SCA"). The SCA provides that Sattel will receive certain MCI
          services from MCI pursuant to the terms and conditions set forth in
          the SCA.

     b.   Sattel desires to be discharged from the performance of its
          obligations set forth in the SCA (the "Obligations").

     c.   CNC desires to receive the MCI services pursuant to the SCA and to
          perform the Obligations.

     d.   MCI desires to release Sattel from the Obligations, provided that CNC
          agrees to perform the Obligations and to be bound by the terms and
          conditions of the SCA and this Agreement.

2.   For the reasons recited above, and in consideration of the mutual
     covenants contained in this Agreement, the parties agree as follows:

     a.   Sattel assigns to CNC the SCA, and CNC accepts such assignment from
          Sattel. CNC has fully read and understands the SCA and assumes and
          shall perform the Obligations.

     b.   CNC agrees to be bound by all of the terms and conditions of the SCA
          in every way, as if it were an original party to the SCA. CNC agrees
          that on August 9, 1996, CNC shall pay MCI [*] and that beginning
          August 16, 1996, CNC shall pay MCI weekly in advance for MCI services
          provided pursuant to the SCA. Such payments shall be via electronic
          wire transfer to MCI's bank account. Such payments must be received 

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<PAGE>
 
          by MCI on Friday of each week by 2:00 PM EST. If the payment date is a
          federal holiday, the payment must be received by 2:00 PM EST the next
          business day. CNC shall make each electronic wire transfer pursuant to
          the instructions set forth below, but MCI may modify these
          instructions upon at least thirty (30) days prior written notice to
          CNC. The amount of CNC's weekly wire transfers shall be [*]. If the
          amount of CNC's prepayments in a calendar month is less than its
          actual invoiced MCI charges for said calendar month, CNC shall pay the
          difference with its next wire transfer to MCI. CNC shall make each
          electronic wire transfer pursuant to the following instructions, and
          understands that failure to do so will result in cancellation of MCI
          services in accordance with MCI Tariff No. 1 filed with the FCC,
          without further notification.

               Bank Name:  The First National Bank of Chicago
               ABA#:  
               DDA #:  
               Acct Name:  MCI Telecommunication Corporation
               Acct#:    
               Cust Name:  Concentric Network Corporation

     c.   MCI releases Sattel from all claims for any liability that has arisen
          or may have arisen with respect to the SCA except for those relating
          to outstanding invoices for MCI services provided by MCI to Sattel
          before the Effective Date. MCI accepts the liability of CNC in lieu of
          the liability of Sattel. MCI shall be bound by the terms and
          conditions of the SCA in every way as if CNC were named in the SCA in
          place of Sattel.

     d.   This Agreement may be signed in counterparts.

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                                      -2-
<PAGE>
 
     In witness whereof; the parties have caused this Agreement to be executed
by their respective authorized representatives.

Sattel Communications LLC                Concentric Network Corporation

By: /s/ Daniel W. Latham                 By: /s/ Michael F. Anthofer
    --------------------------               ----------------------------

Name: Daniel W. Latham                   Name: Michael F. Anthofer

Title:    President                      Title:  Vice President and CFO
      ------------------------                 --------------------------

Date:     August 7, 1996                 Date:   August 7, 1996
     -------------------------                ---------------------------


MCI Telecommunications Corporation

By: /s/ Edward W. Smith
    --------------------------

Name Edward Smith

Title:
      ------------------------

Date:     August 8, 1996
     -------------------------

                                      -3-

<PAGE>
 
                                                                   EXHIBIT 10.17

                  MASTER AGREEMENT FOR MCI ENHANCED SERVICES

        This Master Agreement for MCI Enhanced Services, together with the ESA
Schedules annexed hereto (collectively, the "Agreement"), is made, effective as
of the Effective Date (as defined in Section 2 below), by and between MCI
Telecommunications Corporation and its appropriate affiliated companies
(collectively, "MCI") and Concentric Network Corporation with offices located at
10590 N. Tantau Avenue, Cupertino, California 95014 ("Customer").

1.      MCI Enhanced Service(s).
        ------------------------

1.1     As used in this Agreement, the term "MCI Enhanced Service(s)" means all
commercially available MCI non-Tariffed services and associated equipment
provided by MCI to Customer pursuant to this Agreement and for which an ESA
Schedule has been annexed hereto, and shall not include any MCI Tariffed
services provided pursuant to any filed tariff of MCI or an MCI affiliated
company. The descriptions of MCI Enhanced Services set forth in the respective
ESA Schedules are subject to revision by MCI from time to time.

2.      Service Term: Ramp Period
        -------------------------

2.1     The service term of this Agreement shall commence upon the Effective
Date and end thirty-six (36) months after the expiration of the Ramp Period (as
defined below) (the "Term"). After the expiration of the initial Term, the Term
shall be automatically extended on a month-to-month basis until such time as
either party provides the other with at least ninety (90) days prior written,
notice of termination. The "Effective Date" shall mean the first day of the
first full calendar month following the date upon which this Agreement is
executed by MCI, as indicated on the signature lines below

2.2     The Ramp Period shall begin on the Effective Date and end upon the
earlier of:

2.2.1   thirty (30) days after the date of Customer's written notice to MCI that
the Ramp Period be deemed terminated; or

2.2.2   eight (8) months after the Effective Date.

3.      Revenue Minimum: Underutilization Charges: New Technology
        ---------------------------------------------------------

3.1     During each annual billing period of the Term beginning after the
        expiration of the Ramp Period, (each, an "Annual Period"). Customer's
        Net Usage under this Agreement shall equal or exceed [*] (the "MVR").
        For purposes of this Agreement. "Net Usage" means recurring


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<PAGE>
 
        charges accruing to Customer's account, after application of all
        discounts and credits, including without limitation charges for usage of
        services provided by MCI and for the rental and/or maintenance of
        equipment provided by MCI and excluding without limitation all charges
        expressly excluded in the applicable ESA Schedule and all taxes and
        surcharges.

3.2     If Customer does not satisfy the MVR for any Annual Period, then
        Customer will pay to MCI an underutilization charge (which Customer
        agrees is reasonable) equal to the [*].

3.3     Customer will not be liable for underutilization charges pursuant to
        Paragraph 3.2 above where such underutilization charges arise solely as
        a result of a [*], provided that in any case Customer shall use its best
        reasonable efforts to: (1) direct to MCI new traffic or traffic not
        currently carried by MCI in order to meet the MVR, and (2) retain MCI as
        the provider of the service required pursuant to the [*]. In the event
        Customer's Net Usage falls below [*] of the MVR during any Annual Period
        as the result of a New Technology Change. Customer and MCI shall use
        good faith efforts to renegotiate the terms and conditions of this
        Agreement, including but not limited to all rates and discounts;
        provided, however, that if a new agreement is not reached within sixty
        (60) days after MCI's notice to Customer that Customer's Net Usage has
        fallen below [*] of the MVR during an Annual Period, MCI may terminate
        this Agreement without liability to Customer, upon ninety (90) days
        prior written notice to Customer.

4.      Provision of ESA Services.
        ------------------------- 

4.1     Each MCI Enhanced Service provided under this Agreement shall have a
        corresponding ESA Schedule specifying the applicable rates, discounts
        and other terms and conditions on which MCI will provide such MCI
        Enhanced Service.

4.2     For all domestic and international access services provided in
        conjunction with the MCI Enhanced Services, MCI shall be entitled to
        immediately pass through to Customer any charges, fees, taxes and terms
        and conditions of service imposed by access suppliers, including but not
        limited to increases or decreases in telephone tariffs, communications
        charges and access charges that are imposed or enacted by access
        suppliers to MCI after the Effective Date.


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                                      -2-
<PAGE>
 
4.3     If at any time during the Term MCI tariffs any of the MCI Enhanced
        Services provided pursuant to this Agreement (each a "Newly Tariffed
        Service"). Customer and MCI agree to promptly execute appropriate
        additional agreements and amendments to this Agreement the effect of
        which shall be to eliminate the Newly Tariffed Service from this
        Agreement and to incorporate such Newly Tariffed Service into an
        agreement for MCI Tariffed services. Customer acknowledges and agrees
        that MCI shall have no obligation to include any equipment provided
        under this Agreement or any charges payable for such equipment in any
        such agreement for Tariffed services.

5.      Installation Credits.
        -------------------- 

5.1     Customer shall be eligible for one-time credits in an aggregate amount
        not to exceed [*] to be applied against one-time installation and other
        one-time nonrecurring charges associated with implementation of MCI
        Enhanced Services under this Agreement (the "Install Waiver"). The
        application of the Install Waiver to each MCI Enhanced Service may be
        more specifically described in the applicable ESA Schedule.

6.      MCI Invoices; Payment; Surety.
        ----------------------------- 

6.1     MCI shall invoice Customer on a monthly basis in the month succeeding
        the applicable usage month. Customer shall pay the full amount of each
        invoice, within thirty (30) days after the date of the invoice. MCI may
        use amounts paid by Customer pursuant to any other agreement between the
        parties to offset amounts owed by Customer to MCI pursuant to this
        Agreement. Failure of MCI to timely invoice Customer for any amounts due
        hereunder shall not be deemed a waiver by MCI of its rights to payment
        therefor.

6.2     Upon MCI's reasonable request, Customer shall pay MCI weekly in advance
        for MCI services provided pursuant to this Agreement. Such payments
        shall be via electronic wire transfer to MCI's bank account. Such
        payments must be received by MCI on Friday of each week by 2:00 PM EST,
        if the payment date is a federal holiday, the payment must be received
        by 2:00 PM EST the next business day. Customer shall make each
        electronic wire transfer pursuant to the instructions set forth below,
        but MCI may modify these instructions upon at least thirty (30) days
        prior written notice to Customer. The amount of Customer's weekly wire
        transfers shall be in an amount which is one-fourth of MCI's good faith
        estimate of Customer's actual monthly usage, which estimate may be
        revised from time to time. If the amount of Customer's prepayments in a
        calendar month is less than its actual charges for said calendar month
        as invoiced by MCI pursuant to Paragraph 6.1 above. Customer shall pay
        the difference with its next wire transfer to MCI. Customer shall make
        each electronic wire


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                                      -3-
<PAGE>
 
        transfer pursuant to the following instructions. and understands that
        failure to do so will result in cancellation of MCI services without
        further notification.

               Bank Name:  The First National Bank of Chicago
               ABA#:  
               DDA #: 
               Acct Name:  MCI Telecommunication Corporation
               Acct#: 
               Cust Name:  Concentric Network Corporation

6.3     Customer shall make a separate claim in writing, with adequate support,
        for any credit for service interruption to which Customer believes
        itself entitled under this Agreement, and MCI and Customer will promptly
        address and resolve the claim. The parties shall use reasonable
        commercial efforts to resolve any such claim within sixty (60) days
        after the date of MCI's notice thereof

6.4     Except as otherwise indicated herein, the charges specified in the
        attached Schedule(s) do not include, and Customer agrees to pay, all
        taxes levied by any duly constituted taxing authority against or upon
        MCI Enhanced Services or otherwise arising out of this Agreement
        (including, without limitation, any sales, gross receipts or value-added
        taxes), except any such income tax based on or measured in whole or in
        part by gross or net income, gross or net payments, profits, or net
        worth of MCI or its affiliates (the "Taxes"); so long as, in the case of
        foreign tax withholdings, Customer shall agree to cooperate with MCI in
        providing foreign tax receipts to MCI; utilize best efforts to comply
        with foreign tax laws; and utilize best efforts to provide MCI and/or a
        foreign taxing authority with additional information to support MCI's
        claim for foreign tax credit(s), as requested in writing by MCI.

7.      Customer Obligations
        --------------------

7.1     Customer shall be responsible for obtaining, installing, inter-
        connecting and maintaining all equipment, software and/or communications
        services necessary for inter-connection with MCI's network or otherwise
        for use in conjunction with the MCI Enhanced Services. Customer shall
        ensure that such equipment, software and/or services, including but not
        limited to computer operating systems, are compatible with MCI's
        requirements and that they continue to be compatible with subsequent
        revision levels of MCI-provided equipment, software and services. MCI
        shall exercise reasonable business efforts to provide Customer with
        prior notice of an modifications in MCI's requirements that may affect
        compatibility. Unless otherwise expressly agreed in writing. MCI shall
        have no responsibility for the availability, capacity and/or condition
        of any equipment, software or services obtained by

                                      -4-
<PAGE>
 
        Customer hereunder. Should Customer undertake to connect any MCI
        products or services to any other service or network, Customer shall
        indemnify and hold harmless MCI from any damages, costs, liabilities and
        expenses resulting from such connection or attempted connection,
        including but not limited to damages resulting from unauthorized use of,
        or access to, MCI's network.

7.2     Customer shall take, at its sole expense, all physical and information
        systems security measures reasonably necessary to protect all equipment,
        software and systems provided by MCI and its subcontractors in
        connection with the MCI Enhanced Services, whether owned by Customer,
        MCI, or MCI's subcontractors. Further, Customer shall be responsible for
        ensuring the security of Customer's data, and Customer acknowledges and
        agrees that MCI shall have no liability for any loss resulting from any
        unauthorized third-party access to any Customer data.

7.3     Customer agrees to provide MCI and its subcontractors and their
        respective employees and agents access to Customer's sites where any MCI
        Enhanced Services are provided (including access to associated
        equipment) as reasonably necessary for MCI and its subcontractors to
        perform the MCI Enhanced Services ordered hereunder.

7.4     Customer shall be responsible for obtaining any and all local permits
        and licenses necessary for performance under this Agreement (including
        each ESA Schedule annexed hereto). MCI shall reasonably cooperate with
        Customer to assist in the obtaining of permits. Customer shall indemnify
        and hold harmless MCI, its subcontractors and their respective agents
        and affiliates from and against all damages, costs, liabilities and
        expenses (including reasonable attorneys' fees) arising out of
        Customer's failure to obtain the appropriate permits and licenses.

7.5     Customer is responsible for preparing all equipment installation areas
        at Customer sites with adequate wiring, power sources, telephone
        connections and other physical facilities and services that may be
        necessary to implement the MCI Enhanced Services, and MCI shall have no
        obligation to provide any MCI Enhanced Service that requires equipment
        to be installed at any site(s) where such site requirements have not
        been fulfilled. MCI shall cooperate with Customer to provide site
        requirements.

8.      Software and Documentation.
        -------------------------- 

8.1     All rights, including but not limited to copyright, patent, trademark
        and other intellectual property rights, in any software and/or
        documentation provided by MCI in connection with any MCI Enhanced
        Service shall remain the exclusive property of MCI or its licensor(s).
        MCI grants to Customer a non-exclusive license to use such software and
        documentation solely for Customer's internal business purposes in
        accordance with the terms of this Agreement. No portion of such software
        or documentation shall be copied, decompiled, downloaded, translated, or
        delivered to a third party without MCI's prior written consent,

                                      -5-
<PAGE>
 
        except that Customer shall be permitted to copy MCI-provided software
        for Customer's internal emergency use.

9.      Termination

9.1     A party may terminate this Agreement immediately upon notice to the
        other party if (i) such other party dissolves, discontinues or
        terminates its business to which this Agreement pertains; (ii) such
        other party fails to pay its debts as they become due or admits that it
        is, or is reasonably believed to be, unable to pay its debts as they
        become due; (iii) any bankruptcy, reorganization, insolvency,
        dissolution or similar proceeding is instituted against such other
        party; (iv) such other party makes any assignment for the benefit of
        creditors; or (v) such other parry takes any corporate action in
        furtherance of any of the foregoing.

9.2     MCI may terminate this Agreement immediately upon notice to Customer if
        Customer fails to meet any payment obligation hereunder and such failure
        is not cured within ten (10) business days after Customer's receipt of
        written notice from MCI notifying Customer of such failure. MCI may also
        terminate this Agreement upon thirty (30) days written notice to
        Customer if Customer fails to comply with any other material term of
        this Agreement and Customer does not cure such failure within such
        thirty (30) day period.

9.3     In addition to MCI's rights of termination under Sections 9.1 and 9.2
        above, MCI may, immediately upon written notice to Customer, interrupt,
        suspend and/or terminate any facility, equipment, or service provided
        under this Agreement if:

9.3.1   MCI determines in its sole discretion that continued provision of such
        facility, equipment, or service would contravene any national or
        international regulation, law, or tariff; or

9.3.2   MCI determines that interruption or termination of an MCI Enhanced
        Service is necessary to prevent or protect against fraud or otherwise
        protect its personnel, agents, facilities, or services; or

9.3.3   Any third-party subcontractor or vendor to MCI is unable to continue to
        provide such facility, equipment, or service for any reason; provided,
        however, that where such third party has ceased to provide any facility,
        equipment, or service, MCI will use reasonable efforts to continue to
        provide to Customer a comparable facility, equipment, or service by or
        through another vendor under comparable terms and conditions.

9.4     Customer may terminate this Agreement without further liability to MCI
        upon thirty (30) days written notice to MCI if:

9.4.1   MCI fails to comply with a material term of this Agreement and does not
        cure such failure within such thirty (30) day period; or

                                      -6-
<PAGE>
 
9.4.2   as of the expiration of the Ramp Period, MCI fails to make the following
        MCI locations available to Customer (per those specifications
        communicated by Customer to MCI as of August 13,1996) for inclusion in
        that certain Support Services Agreement by and between the parties,
        dated August 9,1996; provided that such termination right shall be 
                             --------
        deemed to have expired upon Customer's written notice to MCI pursuant to
        Paragraph 2.2.1 above that the Ramp Period be deemed terminated:
        Auburndale, Florida; Austell, Georgia; Downers Grove, Illinois:
        Charlton, Massachusetts and Hillburn, New York.

9.5     In the event Customer terminates this Agreement other than in accordance
        with Section 9.4. then, in addition to any other rights and remedies
        available to MCI. Customer shall pay to MCI an Early Termination Charge
        (which Customer agrees is reasonable) equal to [*].

9.6     Either party may terminate this Agreement without further liability in
        the event that the parties have not, within sixty (60) days after MCI
        Tariffs a service provided pursuant to this Agreement, executed
        appropriate additional agreements and/or Amendments to this Agreement as
        set forth in Paragraph 4.3 above. All of the terms and conditions of
        this Agreement shall apply during said sixty (60) day period, provided
        that such application is permissible pursuant to regulatory and legal
        constraints.

10.     Warranty.
        -------- 

10.1    MCI's warranty obligations, if any, with respect to each Enhanced
        Service shall be set forth in the applicable ESA Schedule. EXCEPT AS
        SPECIFICALLY SET FORTH IN THIS AGREEMENT (INCLUDING THE ESA SCHEDULES),
        MCI MAKES NO WARRANTIES, EXPRESS OR IMPLIED, AS TO ANY MCI ENHANCED
        SERVICES. MCI SPECIFICALLY DISCLAIMS ANY AND ALL EXPRESS OR IMPLIED
        WARRANTIES, INCLUDING WITHOUT LIMITATION ANY WARRANTIES OF
        MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE AND ANY INTELLECTUAL
        PROPERTY WARRANTIES OF ANY TYPE

11.     Indemnification
        ---------------

11.1    Customer agrees to indemnify MCI and its affiliates and their respective
        employees, officers, directors, agents and subcontractors, and hold them
        harmless against any damages and expenses incurred by any of them
        arising out of Customer's acts, omissions and/or breach of its
        obligations hereunder and/or Customer's use of any MCI Enhanced Services
        in a manner other than as contemplated herein, including without
        limitation any use that gives rise to infringement of any patent,
        copyright, trademark, or other proprietary right of a third party,
        except to the extent that such use constitutes a direct infringement by
        Customer of a third party proprietary right that was solely contributed
        to or solely induced by MCI.

- --------------------
        [*] Certain information on this page has been omitted and filed
separately with the Securities and Exchange Commission. Confidential treatment
has been requested with respect to the omitted portions.


                                      -7-
<PAGE>
 
12.     Export and Legal Compliance
        ---------------------------

12.1    The parties acknowledge that certain equipment, software and technical
        data which may be provided hereunder may be subject to export and re-
        export controls under the U.S. Export Administration Regulations and/or
        similar regulations of the U.S. or any other country. No party shall
        export or re-export any such equipment, software, technical data or any
        direct product thereof in violation of any such laws.

12.2    Customer is responsible for complying with alt laws and regulations,
        including but not limited to import and customs laws and regulations.
        MCI shall provide reasonable assistance to Customer and its affiliates
        to facilitate such compliance. Such assistance may include preparation
        of import and customs forms and/or, where requested by Customer, acting
        as Customer's agent in the import process.

13.     Limitation Of Liability.
        ----------------------- 

13.1    NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR ANY CONSEQUENTIAL,
        EXEMPLARY, SPECIAL, INCIDENTAL OR PUNITIVE DAMAGES EVEN IF IT HAS BEEN
        ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

13.2    WITHOUT LIMITATION OF THE PROVISIONS OF PARAGRAPH 13.1 ABOVE, THE TOTAL
        LIABILITY OF MCI TO CUSTOMER IN CONNECTION WITH THIS AGREEMENT SHALL BE
        LIMITED TO THE LESSER OF (A) DIRECT DAMAGES PROVEN BY CUSTOMER OR (B)
        THE AGGREGATE AMOUNTS PAID BY CUSTOMER TO MCI UNDER THIS AGREEMENT FOR
        THE ONE (1) MONTH PERIOD PRIOR TO ACCRUAL OF SUCH CAUSE OF ACTION AND
        FOR THE SPECIFIC PRODUCT OR SERVICE WHICH FORMS THE BASIS FOR SUCH CAUSE
        OF ACTION. THE FOREGOING LIMITATION APPLIES TO ALL CAUSES OF ACTIONS AND
        CLAIMS, INCLUDING WITHOUT LIMITATION BREACH OF CONTRACT, BREACH OF
        WARRANTY, NEGLIGENCE, STRICT LIABILITY, MISREPRESENTATION AND OTHER
        TORTS, FURTHER, NO CAUSE OF ACTION WHICH ACCRUED MORE THAN ONE (1) YEAR
        PRIOR TO THE INSTITUTION OF A LEGAL PROCEEDING ALLEGING SUCH CAUSE OF
        ACTION MAY BE ASSERTED BY EITHER PARTY AGAINST THE OTHER.

        MCI SHALL NOT BE RESPONSIBLE FOR PROTECTION OF TRANSMISSION FACILITIES
        AND CUSTOMER PREMISES EQUIPMENT FROM UNAUTHORIZED ACCESS. MCI SHALL NOT
        BE LIABLE, EITHER IN CONTRACT OR IN TORT, FOR UNAUTHORIZED ACCESS TO, OR
        ALTERATION, THEFT, OR DESTRUCTION OF, DATA FILES, PROGRAMS, OR
        INFORMATION OF CUSTOMER WHETHER OCCURRING THROUGH ACCIDENT OR FRAUD.

                                      -8-
<PAGE>
 
        MCI'S LIABILITY WITH RESPECT TO INDIVIDUAL MCI ENHANCED SERVICES MAY
        ALSO BE LIMITED PURSUANT TO THE TERMS AND CONDITIONS OF THE APPLICABLE
        ESA SCHEDULE.

14.     Confidential Information.
        ------------------------ 

14.1    Neither party shall disclose to any third party during the Term of this
        Agreement, or during the three (3) year period after expiration or
        termination of this Agreement, any of the terms and conditions of this
        Agreement unless such disclosure is lawfully required by any federal
        governmental agency, is otherwise required to be disclosed by law, is
        necessary in any legal proceeding establishing rights and obligations
        under this Agreement or is made to a third party under similar
        confidentiality obligations. Each party reserves the right to terminate
        this Agreement by giving written notice to the other party in the event
        of any unpermitted third party disclosure hereunder.

15.     Miscellaneous
        -------------

15.1    Neither party may assign this Agreement, or any rights or obligations
        hereunder, without the prior written consent of the other party, which
        consent shall not be unreasonably withheld. Any attempted assignment
        without such prior written consent shall be void. Notwithstanding the
        foregoing, MCI may assign this Agreement to its parent or any of their
        subsidiaries or affiliates.

15.2    Other than as the result of an assignment permitted in accordance with
        Paragraph 15.1 above, this Agreement shall not be deemed to provide
        third parties with any remedy, claim, right of action, or other right

15.3    The construction, interpretation and performance of this Agreement, and
        all causes of action arising out of this Agreement, whether in contract,
        indemnity, warranty, strict liability, tort, or otherwise, shall be
        governed as follows: (1) subject to the Communications Act of 1934, as
        amended ("the Act"), by the Act; and (2) as to elements not controlled
        by the Act, by the domestic law of the State of New York without regard
        to its choice of law principles.

15.4    Any dispute arising out of or related to this Agreement, which cannot be
        resolved by negotiations shall be settled by binding arbitration in
        accordance with the J.A.M.S/ENDISPUTE Arbitration Rules and Procedures
        ("Endispute Rules"), as amended by this Agreement. The costs of
        arbitration, including the fees and expenses of the arbitrator, shall be
        shared equally by the parties unless the arbitration award provides
        otherwise. Each party shall bear the cost of preparing and presenting
        its case. The parties agree that this provision and the Arbitrator's
        authority to grant relief shall be subject to the United States
        Arbitration Act. 9 U.S.C. 1-16 et seq. ("USAA"), the provisions of this
        Agreement, and the ABA-AAA Code of Ethics for Arbitrators in Commercial
        Disputes. The parties agree that the arbitrator shall have no power or
        authority to make awards or issue orders of any kind except as expressly
        permitted by this Agreement, and in no event shall the arbitrator have
        the

                                      -9-
<PAGE>
 
        authority to make any award that provides for punitive or exemplary
        damages. The Arbitrator's decision shall follow the plain meaning of the
        relevant documents, and shall be final and binding. The award may be
        confirmed and enforced in any court of competent jurisdiction. All post-
        award proceedings shall be governed by the USAA.

15.5    If any paragraph or clause of this Agreement shall be held to be invalid
        or unenforceable by any body or entity of competent jurisdiction, then
        the remainder of the Agreement shall remain in full force and effect and
        the parties shall promptly negotiate a replacement provision or agree
        that no replacement is necessary.

15.6    If either party fails, at any time, to enforce any right or remedy
        available to it under this Agreement, that failure shall not be
        construed to be a waiver of such party's right to enforce each and every
        provision of this Agreement.

15.7    Any notice or other communication required to be given to the other
        party under this given in Agreement shall be in writing, in the English
        language and either (1) delivered in person, (2) sent by United States
        certified or registered mail, postage prepaid, or (3) sent by an
        overnight courier service, to the following addresses:

15.7.1  If to MCI:

        MCI Telecommunications Corporation
        201 Spear Street
        San Francisco, California 94105
        FAX: 408/978-1220
        Attn: Legal Department

15.7.2  with copy to:

        MCI Telecommunications Corporation
        2560 North First Street, Bldg. F. 2d Floor,
        San Jose, California 95131
        FAX: 415/922-7162
        Attn: Branch Manager


                                      -10-
<PAGE>
 
15.7.3  If to Customer:

        Concentric Network Corporation
        10590 N. Tantau Avenue
        Cupertino, California 95014
        FAX: 408 342-2810
        Attn: Chief Financial Officer

15.7.4  The address for notice may be changed by giving written notice in
        accordance with this Section. If mailed in accordance with this Section,
        notice shall be deemed given three (3) days after mailing. If sent by an
        overnight courier service, notice shall be deemed given one (1) day
        after deposit with the courier service.

15.8    Any delay in or failure of performance by either party under this
        Agreement (other than a failure to comply with payment obligations)
        shall not be considered a breach of this Agreement if and to the extent
        caused by events beyond the reasonable control of the party affected,
        including but not limited to acts of God, embargoes, governmental
        restrictions, strikes (other than those only affecting Customer),
        subcontractor failures or delays, riots, wars or other military action,
        civil disorders, rebellion, vandalism, or sabotage. Market conditions
        and/or fluctuations (including a downturn of Customer's business) shall
        not be deemed force majeure events. The party whose performance is
        affected by such events shall promptly notify the other party giving
        details of the force majeure circumstances, and the obligations of the
        party giving such notice shall be suspended during but not longer than
        the continuance of the force majeure, and the time for performance of
        the affected obligation hereunder shall be extended by the time of the
        delay caused by the force majeure event. In the event that a force
        majeure event occurs, each party has the duty to mitigate or its
        damages.

15.9    Nothing in this Agreement shall create in either party any rights in any
        trademark, trade name, service mark, insignia, symbol, identification
        and/or logotype of the other party. Before either party uses any such
        mark of the other party, it shall obtain the prior written consent of
        the other party.

15.10   This Agreement has been written in the English language and, in the
        event of any conflict or inconsistency between the English-language
        version and any translation hereof the English language version shall
        prevail.

15.11   The headings and captions of the various sections of this Agreement are
        included solely for convenience and shall not be deemed to be a part of
        this Agreement or considered in construing the terms and conditions
        hereof.

15.12   Unless otherwise expressly provided herein, all rights and remedies
        provided for in this Agreement shall be cumulative and in addition to
        every other right and remedy available under this Agreement or otherwise
        at law or in equity.

                                      -11-
<PAGE>
 
15.13   This Agreement, including the ESA Schedules (which are incorporated
        herein by this reference), constitutes the entire agreement between the
        parties hereto with respect to the subject matter hereof, and there are
        no representations, understandings or agreements relative thereto which
        are not fully expressed herein. No amendment, change, waiver, or
        discharge hereof shall be valid unless in writing and signed by an
        authorized representative of the party against which such amendment,
        change, waiver, or discharge is sought to be enforced.

15.14   The parties have duly executed and agreed to be bound by this Agreement
        as evidenced by the signatures of their authorized representatives
        below. Each party represents and warrants to the other that the
        signatory identified beneath its name below has full authority to
        execute this Agreement on its behalf.

15.15   Customer must sign and return to MCI this document in duplicate on or
        before September 18, 1996. After such time, Customer's ability to make
        an offer to MCI consistent with the terms and conditions stated in this
        document shall be deemed terminated.

MCI Telecommunications Corporation     Concentric Network Corporation


By: /s/ Edward W. Smith                By:  /s/ Michael F. Authofer
    -------------------------------         --------------------------------

Name: Edward W. Smith                  Name: Michael F. Authofer
      ---------------                        -------------------------------

Title: Director                        Title: VP & CFO
       --------                               ------------------------------

Date: 10/23/96                         Date: Sept. 11, 1996
      --------                               -------------------------------

                                      -12-
<PAGE>
 
                               ESA Schedule No. 1

               MCI Hyperstream Asynchronous Transfer Mode Service

1.      Description: MCI Hyperstream Asynchronous Transfer Mode (ATM) is a
        connection oriented public/private network data service. Hyperstream 
        ATM - is a cell-based broadband technology which allows seamless high
        speed wide area and local area network connections. A wide range of data
        applications connect with HyperStream ATM including local area network
        (LAN) interconnections, high-speed transmission of digitized, medical
        imaging across the country' and desktop videoconferencing enabling users
        to share multimedia applications.

2.      Rates & Charges; Net Usage.

        [*]



- --------------------
        [*]Certain information on this page has been omitted and filed
separately with the Securities and Exchange Commission. Confidential treatment
has been requested with respect to the omitted portions.

                                      -13-
<PAGE>
 
2.0.1   Monthly Recurring Charges (simplex):

[*]


- -------------------- 
        [*]Certain information on this page has been omitted and filed
separately with the Securities and Exchange Commission. Confidential treatment
has been requested with respect to the omitted portions.

                                      -14-
<PAGE>
 
2.1     "Net Usage" of MCI Hyperstream Asynchronous Transfer Mode Service shall
        include only Recurring Port and Usage Charges, as set forth above. "Net
        Usage" shall not include Nonrecurring Port and Usage Charges or Access
        charges, as set forth above.

3.      [*]



- --------------------
     [*]  Certain information on this page has been omitted and filed
separately with the Securities and Exchange Commission. Confidential treatment
has been requested with respect to the omitted portions.

                                      -15-

<PAGE>
 
                                                                   
                                                               EXHIBIT 10.18    

                                  
                              AMENDED AND RESTATED
                    EMPLOYEE SERVICES AND STAFFING AGREEMENT     

         
     This Amended and Restated Employee Services and Staffing Agreement
("Agreement") dated as of June 19, 1997 by and between Concentric Network
Corporation ("CNC"), a Florida corporation with principal offices at 10590 N.
Tantau Avenue, Cupertino, California 95014 and Critical Technologies
Incorporated ("CTI"), a Delaware corporation with principal offices at 944
Anglum, Hazelwood, Missouri 63042.     

                                       
                                   WITNESSETH      
                                   ----------

         
     WHEREAS, CTI currently assists CNC with planning and implementation of
Points of Presences, network operations, implementation of network improvements
and the opening of "Virtual Local Access" calling areas in accordance with the
terms and conditions of the Employee Services and Staffing Agreement, as
amended, between the parties dated as of November 1, 1995 ("1995 
Agreement");     

         
     WHEREAS, the needs of CNC and the capabilities of CTI have evolved since
November 1, 1995;     

         
     WHEREAS, CTI was acquired by Williams Communications Group, Inc. ("WCG"), a
Delaware corporation on March 6, 1997;     

         
     WHEREAS, WCG has agreed to invest an aggregate of $17 million as further
described and subject to the conditions set forth in that certain Memorandum of
Understanding dated May 30, 1997, between CNC and WCG; and     

         
     WHEREAS, CNC has agreed to modify the 1995 Agreement in recognition of its
current business requirements, CTI's current capabilities and the $3 million
loan.     

         
     NOW, THEREFORE, in consideration of the respective covenants and agreements
of the parties contained herein, the parties hereto agree as follows.     

    
1.   Definitions     
     -----------

         
     For purposes of this agreement, certain words and phrases are defined as
follows.     

             
         (a)   POP:  "Point of Presence" is a local access network node on a
network.     

             
         (b)   Staff Month:  One calendar month of staff time including sick
time, weekends, holidays and vacation time. There are 12 such periods in each
calendar year.     

             
         (c)   Loaned Employee:  An employee of CTI, the services of which are
utilized by CNC to facilitate the goals and purposes of this Agreement.      
<PAGE>
 
              
         (d)   "Local Access Network Engineering and Design Services" and "Local
Access Network Design and Analysis":  The modeling of traffic patterns and
expenses to determine the most effective method for expanding and modifying a
network's dial-in access nodes.     

             
         (e)   Network Expansion Plan and Network Operations Plan:  A series of
mutually agreed upon objectives and goals that are exhibits to this 
Agreement.     

             
         (f)   Existing POP Site Contract:  The existing location management
contract between CNC and CTI, titled Collocations Services Agreement, dated
November 1, 1994, as amended, and attached as an exhibit to this contract.     

             
         (g)   Reasonably Attainable:  Tasks that could be completed by a group
of similar size and experienced individuals with the same capital flexibility
allowed by CNC. Additionally, the sum total of activities must also be able to
be completed by the group.     

             
         (h)   Provisioning:  The process of contracting for the physical
facility where a POP will be located and coordinating the telephone and other
equipment orders necessary to bring this site live or into production use by the
network.     

             
         (i)   Co-locate:  The ability of CTI to place equipment on a POP site
which is owned by CNC. The concept being that both organizations can utilize the
space which is owned or leased by CNC.     

             
         (j)   Confidential Information:  All information marked as
"Confidential" shall be considered "Confidential Information." It shall be the
responsibility of the originator of the Confidential Information (the
"Originator") to clearly mark the information as confidential to be received by
the Recipient ("Recipient"). When information deemed to be Confidential is
provided orally, the Originator shall, at the time of disclosure, identify the
information as Confidential and provide the Recipient a dated written summary of
the Confidential Information so disclosed promptly after such oral disclosure.
Confidential Information shall not include (a) information previously known by
the Recipient, (b) information that is publicly available or becomes publicly
available other than through unauthorized disclosure by the Recipient, (c)
information that is received from a third party whose disclosure does not
violate any confidentiality obligation to the Originator, (d) information
developed by or on behalf of the Recipient independent of the Confidential
Information received from the Originator or information required to be disclosed
pursuant to the Federal securities disclosure laws.     

             
         (k)   Financing Event:   An initial public offering by CNC or, in the
alternative, some other private financing in either event totaling no less than
$40 million (including for such purposes an aggregate of $15 million to be
invested in CNC by WCG as further described in this sentence) to be completed no
later than October 31, 1997 in which WCG agrees to purchase at least $12 million
of CNC common stock and, if requested by CNC, to convert the $3 million loan in
accordance with the Convertible Promissory Note of even date herewith.  In the
event that an initial public offering is not consummated, but a private
Financing Event occurs, WCG will, subject to the satisfactory completion of due
diligence and the receipt of necessary corporate and other approvals,      

                                      -2-
<PAGE>
 
     
invest $12 million and, if requested by CNC, convert the $3 million loan, if the
terms and conditions as set by the lead investor of the private Financing Event
are acceptable to WCG. WCG's investment participation in the Financing Event is
expressly contingent upon CNC's satisfaction of all the conditions set forth in
Sections 3, 4, 5, and 6 of the Memorandum of Understanding between CNC and WCG
dated May 30, 1997.     

              
         (l)    Best Efforts:   A "best efforts" obligation shall mean the
highest level of commercial effort without requiring a party to incur a loss or
an extraordinary expense in performing such efforts.     


    
2.   CTI's Responsibilities and Objectives     
     -------------------------------------

         
     Loaned Employees - Additional Responsibilities     

         
     2.1  CTI hereby agrees to use its best efforts to provide certain key
employees of CTI, whose names are set forth on Exhibit A hereto (the "Loaned
Employees"), to perform functions for CNC.     

         
     Although each Loaned Employee shall at all times remain an employee of CTI,
he or she will perform duties and be under the general direction of CNC for the
term of this Agreement, or until such Loaned Employee's assignment is otherwise
terminated as provided in Section 4 hereof.  The Loaned Employees hereunder
shall be located in St. Louis, Missouri, unless noted in Exhibit A.     

         
     The parties hereto agree that the position and title with respect to each
Loaned Employee are as set forth on Exhibit A hereto.  Exhibit A hereto may be
amended in writing from time to time by the parties hereto to add Loaned
Employees to fill positions provided for under the Network Expansion Plan and
Network Operations Plan previously submitted by CTI to CNC, and any other plans
submitted by CTI and agreed to by CNC.  Copies of said Network Expansion Plan
and Network Operations Plan, marked Exhibits B and C respectively, are attached
hereto and incorporated by reference as if fully set out herein.  Exhibit A may
also be amended to reflect the termination of a Loaned Employee's assignment
pursuant to Sections 4.1 and 4.3 hereof, to replace a Loaned Employee whose
assignment is terminated pursuant to Section 4.1 of this Agreement, or to alter,
amend or revise the title, salary and duties of any Loaned Employee.     

         
     2.2  CTI and CNC acknowledge that it is important for CNC to have long term
control and ownership of the Network Operations function being performed, in
part, by loaned CTI employees under this Agreement.  CTI and CNC further
acknowledge that CTI has current and prospective customers for which a 24x7x365
day network operations infrastructure is required. The parties further
acknowledge that in order to meet CNC's timetable for implementation of its new
Network Operations function, CTI was utilized to hire staff and implement the
technology necessary to provide CNC with a 24x7x365 day network operations
function.  To accomplish this objective, CTI recruited a number of people who
had been identified as being members of the planned CTI network operations
center.     

                                      -3-
<PAGE>
 
         
     In recognition of the facts that a) CTI had intended to build its own
network operations center around some of the core staff hired by CTI to support
CNC's requirements, b) CNC funded virtually all of the build out expense for the
Network Operations Center in St. Louis as well as the monthly operating expense
for this center, c) CNC requires the flexibility of controlling this function as
a core asset of CNC, and d) CTI desires the ability to service non-CNC customers
with its own dedicated staff plus some portion of the CNC staff, equipment,
software, and other resources funded by CNC on an "as available" basis, the
parties agree that the following terms will apply with respect to the Network
Operations staff as identified on Exhibit A and with respect to the resources
that are covered by this Agreement.     

         
     A)  CTI will reimburse CNC for a proportionate share of the costs of a)
Loaned Employees, b) CNC employees who have been converted from CTI-to-CNC
employment, and c) supporting resources that have been or are being paid for by
CNC when these people or supporting resources are used to support non-CNC
customer networks.  The amount of reimbursement will be computed as TCxAC1 /
(AC1+C2):     

         
     NOTE:  A negative result, product, or sum will not result in payment to
CTI.     

              
          TC=  Monthly expense paid to CTI for Network Operations Loaned
               Employees, plus Monthly expenses of any/all CNC hired Network
               Operations employees, plus Monthly amortization/depreciation (48
               months) of the Network Operations capital equipment, software,
               and site preparation expenses paid for by CNC, plus any other
               expenses associated with Network Operations paid for by CNC.     

              
          C1=  Total number of help/trouble calls taken by Network Operations
               from Non-CNC customers.     

              
          C2=  Total number of help/trouble calls taken by Network Operations
               from CNC customers.     

              
          CP=  Calls per employee (Total calls divided by total of Network
               Operations personnel paid for by CTI and CNC).     

              
          NR=  Number of CTI Network employees not reimbursed by CNC.     

              
          AC1= C1-(NRxCP).     

         
     2.3   Loaned Employees, who will be made available to CNC, will be
available only after they have executed Letters of Agreement in the form
attached hereto as Exhibit D, which form the parties hereto expressly 
approve.     

                                      -4-
<PAGE>
 
          
     2.4   CTI agrees to exercise due diligence in overseeing those with access
to the Confidential Information.  CTI agrees to limit the number of its
associates, officers, or employees,  who are exposed to  the Confidential
Information.  The standard of care to be used in preventing disclosure of the
Confidential Information shall be at least as great as that care CTI would take
in preserving the confidentiality of its own trade secrets and proprietary
information.     

         
     2.5   The parties hereby acknowledge and agree that Intellectual Property
Rights, as defined in Exhibit B, created, written, developed or made by each
Loaned Employee while performing services for CNC pursuant to this Agreement
shall be subject to the addendum to the Loaned Employee Letter of Agreement
(Exhibit D).     

         
     2.6   In addition to the other terms and conditions of this Agreement, CTI
and CNC agree and stipulate, as further consideration for the promises made by
each party hereunder, that CTI will use its best efforts to ensure that a
properly trained network control center is developed in St. Louis, Missouri.
This will include developing the staffing requirements, interviewing and hiring
the staff, and training the staff as required.     

    
3.   Agreement Scope and Term     
     ------------------------

         
     The term of this Agreement shall be for a period commencing June 19, 1997,
and terminating on December 31, 2000.  The parties agree that this Agreement may
be terminated prior to December 31, 2000 by the mutual, written consent of both
parties.  Such contract period referred to herein shall be referred to as the
"Agreement Term".  This Agreement shall automatically renew for an additional
two-year period unless either party shall give one-hundred twenty (120) days
notice prior to the expiration of this Agreement to the other party that said
party does not wish to extend the terms of this Agreement.  Notwithstanding the
foregoing, if WCG elects not to participate in the Financing Event, even though
CNC has satisfied all conditions set forth in the definition of Financing Event,
this Agreement may be terminated by CNC on October 31, 1999, if CNC provides CTI
ninety (90) days prior written notice.     

    
4.   Termination of Assignments     
     --------------------------

         
     A Loaned Employee's assignment to CNC may be terminated by CTI for the
following reasons:     

         
     4.1   Termination of Employment with CTI.  In the event a Loaned Employee's
           ----------------------------------                                   
employment with CTI terminates for any reason, the Loaned Employee's assignment
to CNC hereunder shall also terminate.  Subject to Section 9, nothing in this
Agreement shall require CTI to retain the Loaned Employee in its employment for
any period of time, and CTI shall be free to terminate any Loaned Employee at
any time during the term of this Agreement.     

         
     4.2   Payments Due Upon Termination of Loaned Employee's Assignment.  Upon
           -------------------------------------------------------------       
the termination of the assignment of a Loaned Employee, CNC shall reimburse CTI
for any amount which had accrued and remains unpaid as of the date such
assignment terminated and for which CTI is      

                                      -5-
<PAGE>
 
    
entitled to reimbursement under Section 5 below. CNC shall make any payments due
under this Subsection in accordance with said Subsection 5.6.     

         
     4.3   Replacement of Loaned Employees.  In the event a Loaned Employee's
           -------------------------------                                   
assignment is terminated pursuant to Subsection 4.1 above, unless the position
held by the Loaned Employee has been eliminated, CTI shall select a replacement
employee mutually satisfactory to CNC who will become a Loaned Employee for
purposes of this Agreement.     

    
5.   CNC's Obligations - Compensation, Benefits and Other Human Resource Plans
     -------------------------------------------------------------------------
     and Programs and Reimbursement of Expenses     
     ------------------------------------------

         
     5.1   Loaned Employees Generally.  Except as otherwise set forth below in
           --------------------------                                         
Subsection 5.4, there shall be no change, from the date of this Agreement, in
the amount, terms and conditions of CTI's compensation, benefit and other Human
Resource ("HR") plans and programs (currently [*] of Base Salary Rate as
defined below) as they relate to the Loaned Employees during the term of this
Agreement without consultation with and the written consent of CNC, except such
changes as may be made in the ordinary course of business consistent with WCG's
past practices.  CNC recognizes that CTI Loaned Employees participate in plans
and programs sponsored by WCG.     

         
     5.2   Base Salary.  CTI shall continue to compensate each of the Loaned
           -----------                                                      
Employees for his or her services to CNC under the terms of this Agreement at
the rate per annum as set forth in the monthly CTI invoices paid by CNC and as
adjusted annually in accordance with the next sentence, plus overtime and
bonuses, if any, ("Base Salary Rate"), less appropriate deductions (including
withholding taxes and deductions for participation in benefit programs), and in
accordance with CTI's general payroll practices.  Any increase in such Base
Salary Rate may only be implemented with the approval of CNC.     

         
     5.3   Benefits and Perquisites.  Each Loaned Employee shall be eligible to
           ------------------------                                            
continue in, or receive benefits under the benefits plans, arrangements,
practices, and programs made available from time to time to similarly situated
employees of CTI, subject to, and on a basis consistent with, the terms of such
plans, arrangements, practices, and programs.     

         
     5.4   Incentive Compensation.  Each Loaned Employee may be considered for
           ----------------------                                             
participation in any incentive compensation, deferred compensation or bonus
arrangement, plan, policy and practice of CTI during the Agreement Term in the
sole discretion of CTI, subject (1) to and on a basis consistent with the terms
of any such arrangement, plan, policy, and practice and (2) to the prior written
approval of CNC which shall be given in CNC's sole discretion.     

         
     5.5   Reimbursement of Loaned Employee Expenses.  During the Agreement
           -----------------------------------------                       
Term, CNC shall reimburse CTI on a monthly basis for all reasonable ordinary and
necessary out-of-pocket employment related expenses of all Loaned Employees,
including, but not limited to travel, meals, lodging, mileage, moving expenses,
telephone calls, out-of-pocket advances made by the Loaned Employee on behalf of
CNC, and any other reasonable employment related expense, including any personal
income tax liability that is a direct result of relocating. This provision shall
also include all network operations employees hired in St. Louis, Missouri.     

 
    
[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.     

                                      -6-
<PAGE>
 
          
     5.6   Reimbursement of Direct Costs of Network Operation.  CNC shall also
           --------------------------------------------------                 
reimburse CTI for the direct costs of Network Operation.  CNC shall reimburse
CTI, on a monthly basis, for office rent, electricity, telephone service,
including base service and long distance, necessary office furniture and
equipment, ongoing network communications cost, software, insurance, and any
other direct, reasonably necessary expense.     

         
     5.7   Reimbursement of CTI     
           --------------------

               
           A)  During the Agreement Term, CTI shall invoice CNC monthly for one-
twelfth (1/12) of the annual compensation, benefits and administrative costs
incurred by CTI with respect to the Loaned Employees, as referenced in
Subsections 5.1, 5.2, 5.3 and 5.4 and as determined by CTI, and CNC shall pay
such amount to CTI in accordance with its normal payment practices, but in no
event later than thirty (30) days following receipt of such invoice for such
amount.  Any discrepancies between amounts billed and paid and actual costs
incurred by CTI shall be reconciled and paid within thirty (30) days following
CTI's submission to CNC after the end of the relevant calendar year of a Year
End Reconciliation.  CNC shall be responsible for reimbursement of the items set
forth in this Section including the following: Loaned Employees' salaries, FICA,
state and federal unemployment tax, worker's compensation insurance premiums and
deductibles, medical/health insurance premiums and dental insurance premiums,
including coverage for spouses and family, long-term disability insurance
premiums, life insurance premiums, seminars and training costs related to
Network Operations, local and long distance travel expenses, pagers.  CNC shall
be responsible for reimbursement of other costs or expenses which CNC deems
reasonable and necessary.     

               
           B)  CNC shall also pay to CTI, as reimbursement, an amount equal to
[*] of the base salary for those Loaned Employees who were working for CNC as
of November 1, 1995, and an amount equal to [*] of the base salary for those
Loaned Employees who began working for CNC after November 1, 1995. These rates
reflect a [*] and [*] mark-up, respectively, of the base salaries of the
Loaned Employees, plus an imputed benefits rate of [*].     

               
           C)  CNC shall have the right to audit, at CNC's expense, CTI's
expenses, costs and billings under the Section 5 within sixty (60) days of the
date of the Year End Reconciliation.  If CNC does not contest the Year End
Reconciliation within ninety (90) days of the date of the Year End
Reconciliation, then CNC will be deemed to have agreed with the Year End
Reconciliation and shall waive any right to contest or challenge any cost,
expense, payment, markup or other charge incurred or calculated by CTI for the
period covered by the Year End Reconciliation.     

    
6.   Agreement Transition     
     --------------------

         
     In order to provide an orderly transition at the end of the Agreement, CTI
agrees that, prior to the Agreement's termination, to locate all personnel and
resources used to support CNC to a new subsidiary and transfer that entity to
CNC according to the following plan:     

    
A.   CTI will create a wholly-owned subsidiary.  CTI will transfer all Loaned
     Employees to this entity.     


    
[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.     

                                      -7-
<PAGE>
 
     
B.   CTI will transfer the lease (including leasehold improvements) to 3324
     Hollenberg Drive to this new subsidiary. Said lease to have at least five
     (5) years remaining at the termination of this Agreement at a cost not to
     exceed $12 per square foot (triple net). Any office equipment currently
     owned by CTI and used exclusively by the subsidiary employees will also be
     transferred. Additional office equipment for current or future employees of
     the subsidiary will be paid for by CNC and remain their assets.     

    
C.   CTI will transfer a nonexclusive, nontransferable, non revocable license to
     its proprietary software for network modeling, site management, and telco
     reconciliation to this new entity. Such license will restrict the use of
     the software to CNC internal business needs and the licensed software shall
     not be sublicensed or used in a "service bureau" capacity.     

    
D.   CNC shall acquire title to this new subsidiary at the end of this Agreement
     and CTI will vacate the premise on 3324 Hollenberg Drive. Both parties
     agree to execute such documents as may be necessary to minimize the tax
     effect to both entities.     

    
E.   CNC shall pay CTI [*] for relocation expenses and the assets of the
     new subsidiary. This amount will be paid to CTI as needed to reimburse CTI
     for its costs in relocating its other business to other facilities. CTI
     will provide to CNC on at least a quarterly basis their projected needs for
     the next six months. All of these funds could be paid in advance of the
     completion of this Agreement. Any funds not so advanced will be paid at the
     point where ownership of the subsidiary transfers to CNC.     

    
F.   CTI agrees to reimburse CNC an amount equal to 35% of the annual salary of
     any CNC employee (acquired through the acquisition of the subsidiary) that
     returns to WCG, CTI or their affiliates within one year of said
     acquisition.     

    
G.   CTI agrees to use its best efforts to ensure that all employees of the
     subsidiary stay with the entity when the transfer to CNC occurs.     

    
7.   Consulting Services     
     -------------------

         
     CTI agrees to provide other consulting services to CNC as requested by CNC
at a rate not to exceed the lowest offered by CTI to other unaffiliated
customers requiring similar services (including duration or quantity of such
services). Both parties agree to work in good faith to negotiate and agree to
the other material terms and conditions of the consulting services 
provided.     

    
8.   Mutual Recommendation     
     ---------------------

         
     Each party agrees to recommend the other party as business opportunities
arise.  In this regard, CNC will recommend CTI services, as appropriate, to
STET/TMI.     

    
9.   Agency and Authority     
     --------------------

     
[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.     


                                      -8-
<PAGE>
 
          
     The Loaned Employees shall remain, and shall be advised by the parties that
they will at all times during the Agreement Term, continue as employees of CTI;
provided, that notwithstanding anything to the contrary contained in this
Agreement, CTI may, at any time, with cause, terminate employment of such Loaned
Employee with CTI.  If a Loaned Employee is to be terminated without cause, such
termination shall be approved by CNC prior to CTI's termination of such
employee.  CNC shall be responsible for directing the Loaned Employees'
performance of duties associated with the position titles set forth on Exhibit A
hereto.  The parties hereto agree that until further agreement, the Loaned
Employees are not, nor will they become, employees of CNC for tax purposes or
any other purpose whatsoever.  The Loaned Employees have no authority to make
commitments or enter into contracts on behalf of, or to bind or otherwise
obligate CNC in any matter whatsoever, except as expressly provided herein.     

    
10.  Indemnification     
     ---------------

         
     10.1  In the event of any liability, claim or cause of action of any kind
against CNC arising out of any action or inaction (or alleged action or
inaction) of a Loaned Employee, which is outside the scope of such employee's
services for CNC or as contemplated hereunder, or arising out of any action or
inaction (or alleged action or inaction) of a Loaned Employee which is outside
of the scope of such employee's services for CTI, CTI shall indemnify CNC from
and against any and all losses, damages, claims, penalties, liabilities or
expenses (including reasonable attorneys' fees and expenses) ("Losses") incurred
by CNC.  CTI shall be informed immediately by CNC of any alleged action or
inaction by any CTI employee which might give rise to a claim for losses by 
CNC.     

         
     10.2  In the event of any claim or cause of action of any kind against CTI
by any Loaned Employee for violation of any employment law, the Americans with
Disabilities Act, the Family and Medical Leave Act, or any act or law designed
to protect the rights of employees, arising out of any action or inaction (or
alleged action or inaction of CNC or any of its employees, principals, agents,
or representatives), CNC shall indemnify CTI from and against any and all losses
or costs, damages, claims, penalties, liabilities, or expenses (including
reasonable attorneys' fees and expenses).     

         
     10.3  CTI shall indemnify and hold harmless CNC from and against any and
all Losses incurred by CNC arising out of, or resulting from or relating to any
action by CTI relating to termination, salary continuation, indemnity, notice
pay or severance pay or benefits payable by reason of termination of employment
of any Loaned Employee with CTI or termination of the assignment of any Loaned
Employee with CNC, unless said claim or loss is the result of a reduction in
force for employees specifically hired at the request of CNC, or results from
termination because such employee is hired by CNC.     

    
11.  Successors and Assigns     
     ----------------------

         
     This Agreement and all rights hereunder shall inure to the benefit of and
be enforceable by each party's successors and permitted assigns.  No party may
assign or transfer this Agreement or transfer its rights or obligations
hereunder without the prior written consent of the other party (which consent
shall not be unreasonably withheld) except to an affiliate.     

                                      -9-
<PAGE>
 
    
12.  Governing Law and Jurisdiction     
     ------------------------------

         
     This Agreement shall be governed by, and construed in accordance with, the
laws of California, without regard to the principles of conflicts of laws
thereof.     

    
13.  Notices     
     -------

         
     For the purposes of this Agreement, notices and all other communications
provided for in this Agreement shall be in writing and shall be deemed to have
been duly given or delivered upon receipt after personal delivery or mailing by
registered mail, return receipt requested, postage prepaid, address as 
follows:     

               
           (a) If to CTI:     

                   
               Critical Technologies Incorporated
               Attn: Gordon Martin
               111 East First Street
               Tulsa, OK 74103-2808
               Phone:       

                   
               with a copy to:      

                   
               General Counsel
               Williams Telecommunications Group, Inc.
               One Williams Center
               Suite 4000
               Tulsa, OK 74172
               Phone:  
               Facsimile:       

                                     -10-
<PAGE>
 
               
           (b) If to CNC:      

                   
               Concentric Network Corporation
               10590 N. Tantau Avenue
               Cupertino, CA 95014
               Attention:  Chief Financial Officer
               Phone:  (408) 342-2800
               Facsimile:  (408) 342-2810      

                   
               with a copy to:      

                   
               Wilson, Sonsini, Goodrich & Rosati
               650 Page Mill Road
               Palo Alto, CA 94304
               Attention: David J. Segre
               Facsimile:  (415) 493-6811      

    
or to such other address as any party may have furnished to the other in writing
in accordance herewith.      

    
14.  Amendment      
     ---------

         
     No amendment or modification of this Agreement or any of its provisions
shall be binding upon any party unless made in writing and signed by all of the
parties hereto.      

    
15.  Validity      
     --------

         
     The invalidity or unenforceability of any provisions of this Agreement
shall not affect the validity or enforceability of any other provision of this
Agreement.      

    
16.  Waiver      
     ------

         
     The performance of any condition or obligation imposed hereunder upon any
party hereto may be waived only upon the written consent of the parties hereto.
Such waiver shall be limited to the terms thereof and shall not constitute a
waiver of any condition or obligation of the other party under this Agreement.
Any failure by any party to this Agreement to enforce any provision shall not
constitute a waiver of that or any other provision of this Agreement.      

    
17.  Third Party Rights      
     ------------------

         
     This Agreement shall not inure to the benefit of any third party other than
CTI and CNC and valid successors or assigns of a party hereto or thereto.      

                                     -11-
<PAGE>
 
    
18.  Remedies Upon Default      
     ---------------------

         
     The parties agree that they will attempt to resolve disputes arising in
connection with this Agreement through good faith consultation.  In the event of
a default by either party, the other party shall notify the defaulting party, in
writing, of the default, setting forth the nature thereof. Said notice shall be
mailed to the company at the designated address for notices as provided in
Section 13 above.  The defaulting party shall have thirty (30) days from the
date of the notice to cure said defect or default.  In the event said defect or
default is not cured within thirty (30) days as provided herein, the non-
defaulting party may declare this contract in breach and may pursue any legal or
equitable remedy, including specific performance, provided that, except as
expressly and specifically set forth in another paragraph to this Agreement,
neither party shall be liable to the other party for any lost profits; any loss
of business; any cost of replacement services; or any indirect, consequential,
incidental or special losses or damages of any kind or nature whatsoever, due to
such default or defect. The parties agree that in the event of such a breach of
contract action, the losing party shall be responsible for the payment of all
costs, including the reasonable attorney's fees of the prevailing party.      

    
19.  Headings      
     --------

         
     The heading references are for convenience purposes only and do not have
any meaning with respect to the terms and conditions of this Agreement.      

    
20.  Force Majeure      
     -------------

         
     Neither CNC or CTI shall be considered in default in performance of their
obligations hereunder (except the payment of monetary obligations) if
performance of such obligations is prevented or delayed by acts of God or
government, labor disputes, failure or delay of transportation, or by vendors or
subcontractors, or any other similar cause or causes beyond the reasonable
control of either party.  Time of performance of either party's obligations
hereunder shall be extended by the time period reasonably necessary to overcome
the effects of such force majeure occurrences.      

                                     -12-
<PAGE>
 
          
     IN WITNESS WHEREOF, the parties have executed this Agreement by their duly
authorized representatives as of June __, 1997.      


    
CONCENTRIC NETWORK                      CRITICAL TECHNOLOGIES
CORPORATION                             INCORPORATED

By: /s/ (Signature Appears Here)        By: /s/
   --------------------------              --------------------------
Name:                                   Name:
     ------------------------                ------------------------
Title:                                  Title:
      -----------------------                 -----------------------
     
                                     -13-
<PAGE>
 
                   LIST OF EXHIBITS AND SCHEDULES TO EMPLOYEE
                   ------------------------------------------
                        SERVICES AND STAFFING AGREEMENT
                        -------------------------------

                                    EXHIBITS
                                    --------
<TABLE> 
<S>            <C> 

A.             List of Loaned Employees

A(1).          Stock Grant Recipients and Amounts

B.             Employee Letter of Agreement

B.(addendum)   Confidentiality Agreement

C.             Network Expansion Plan

D.             Performance (Stretch) Objectives

E.             Network Operations Plan

F.             Form for Notice of Election of Exercise of Grant Option

G.             Form of Option Agreement

H.             Collocations Services Agreement

I.             Software Development Plan

</TABLE> 
                                   SCHEDULES
                                   ---------

1.        Additional Covenants and Agreements regarding the grant and exercise
          of Option Shares.

2.        Disclosure by CNC of grants of other options, warrants or other rights
          to acquire shares of CNC stock or other equity securities of CNC.
<PAGE>
 
[***]                                EXHIBIT A




- -------------------------

     [***]Certain information in this exhibit has been omitted and filed
separately with the Securities and Exchange Commission.  A total of 3 pages
containing such information has been omitted from this exhibit.  Confidential
treatment has been requested with respect to the omitted portions.
<PAGE>
 
                            "EXHIBIT B (ADDENDUM)"

           CONFIDENTIALITY, NON-COMPETITION, AND COPYRIGHT AGREEMENT


     THIS AGREEMENT is made as of the _____ day of __________, 1995, between 
CONCENTRIC RESEARCH CORPORATION, a Florida corporation (hereinafter referred to 
as "CRC"), and __________________________ (hereinafter referred to as 
"Employee").


                                  WITNESSETH:

     WHEREAS, CRC owns and operates the Concentric Research Information System 
("CRIS"), a computerized, on-line interactive network that provides information,
entertainment and telecommunication services; and

     WHEREAS, in connection therewith CRC develops proprietary computer software
and uses proprietary know-how in such business, and now has and expects to 
develop confidential information relating thereto and in connection with other 
software products or services CRC develops or offers in the future; and

     WHEREAS, the parties hereto desire to set forth certain agreements and 
understandings regarding ownership of intellectual property by CRC and 
confidentiality and non-competition on the party of Employee, which agreements 
and understandings are for the benefit of both CRC and Employee.

     NOW, THEREFORE, in consideration of the foregoing, of the mutual promises 
herein contained, and of other good and valuable consideration, the receipt and 
sufficiency of which is hereby acknowledged, it is hereby agreed as follows:

1.        Confidential Information.
          ------------------------

          a.        The term "Confidential Information" shall refer to any 
information, not generally known in the relevant trade or industry, which was 
obtained from CRC, or which was learned, discovered, developed, conceived, 
originated or prepared during or as a result of the performance hereunder on 
behalf of CRC and which falls within the following general categories:

          i.   information relating to trade secrets of CRC;

          ii.  information relating to existing or contemplated products,
               services, technology, designs, processes, formulae; computer
               systems, computer software, algorithms and research or
               developments of CRC;
<PAGE>
 
        iii.  information relating to business plans, sale or marketing methods,
              methods of doing business, customer lists, customer usages and/or
              requirements, names of sales representatives, and vendor and
              supplier information or CRC;

        iv.   information relating to proprietary computer software not
              generally known to the public and related unpublished
              documentation of proprietary computer programs;

        v.    information relating to new developments;

        vi.   any other information that CRC may wish to protect by patent, 
              copyright or by keeping it secret and confidential.

        b.    Employee agrees not to divulge to anyone, at any time during or 
after the termination of his employment by CRC, any Confidential Information or 
any other trade secrets of CRC. Upon the termination of his employment by CRC, 
Employee agrees to deliver up to CRC all notebooks, computer files and any other
data in any tangible form whatsoever in relation thereto, containing, embodying 
or evidencing any of the Confidential Information described herein.

2.      Non-Competition Covenant.
        ------------------------

        a.    The term "Competitor" shall refer to any person, firm, 
corporation, partnership or other business entity of any type whatsoever engaged
in or about to become engaged in the production, licensing, sale or marketing of
any product or service:

        i.    which is similar to or competitive with CRIS or CRC's proprietary
              computer software or any product or service of CRC with which
              Employee has been directly concerned through his work with CRC
              during the preceding two (2) years;

        ii.   with respect to which the Employee has acquired Confidential 
              Information.

        b.    As material inducement to CRC's willingness to employ Employee, 
Employee covenants and agrees that, for a period of two years following the 
termination of his employment, whether such termination be with or without 
cause, he shall not enter the employ of any Competitor, nor himself engage 
during such period, directly or indirectly as principal, agent, officer, 
employee or otherwise, in any such business in competition with CRC, within any 
area in which CRC is itself carrying on business at the time of such 
termination. Employee also covenants and agrees that for a period of two years 
following termination of his employment, he shall not recruit or attempt to 
recruit any of CRC's other employees, or to contact either directly or 
indirectly, any client of CRC for the purpose of soliciting such client from 
CRC.

3.      Copyright Assignment. Employee hereby acknowledges that all works,
        --------------------
including all program code and supporting documentation and all other 
copyrightable materials, written in whole

                                      -2-
<PAGE>
 
or in part by Employee, shall be deemed to be works made for hire. To the extent
that any such writing may not, by operation of law, be works make for hire,
Employee hereby assigns to CRC the ownership of copyright in such works, whether
published or unpublished. Employee agrees to give CRC or its designees all
assistance reasonably required to perfect such rights, including but not limited
to, the identification of the works and supporting documentation and the
execution of any instruments required to register copyrights.

4.        Remedies. The parties hereto recognize that the services to be
          --------
performed hereunder by Employee are special and unique. It is understood and
agreed that Employee's disclosure of Confidential Information, breach of the 
Non-Competition Covenant, and/or breach of the Copyright Assignment, may give
rise to irreparable injury to CRC, which may not be adequately compensated by
damages. Accordingly, in the event of Employee's breach or threatened breach of
this Agreement, CRC shall be entitled to preliminary and permanent injunctive
relief, without bond, restraining Employee from disclosing, in whole or in part,
the Confidential Information protected by this Agreement, or from rendering any
services to any person, firm, corporation, association, or other entity to whom
such Confidential Information, in whole or in part, has been disclosed or is
threatened to be disclosed, or from marketing, selling, or otherwise exercising
proprietary rights to copyrightable material referenced in this Agreement.
Nothing herein shall be construed as prohibiting CRC from pursing any other
recovery of damages. These undertakings shall survive the termination or
cancellation of this Agreement or of Employee's employment with CRC.

5.        Miscellaneous Provisions.
          ------------------------ 

          a.   Employee acknowledges that he has no employment agreement of any
type whatsoever, whether oral, written, expressed, or implied, that would alter
the "at will" status of Employee's employment with CRC. Both CRC and Employee
therefore have the right to terminate this employment relationship at any time
for any reason, with no obligation to provide advance notice of such termination
to the other party. Employee hereby acknowledges receipt of the CRC employment
manual and agrees that CRC shall have the unilateral right to modify its
employment policies therein described at any time. Employee further agrees and
acknowledges that these employment policies or other similar provisions are
reasonable and agrees not to contest them by way of unjust dismissal proceedings
otherwise. By signing this Agreement, however, Employee is not agreeing to forgo
or waive any rights that he has or may have under federal, state and local
employment laws or regulation.

          b.   Employee represents to CRC, which relies on this representation,
that Employee is free to enter into this Agreement in that he is not under any
restrictions from a former employer or business that would preclude him from
making these arrangements. Employee acknowledges that CRC does not want him to
disclose to it any confidential information that he may have obtained from a
former employer.

          c.   This Agreement will be binding upon, shall inure to the benefit
of, CRC and Employee, and their respective heirs, personal and legal
representatives, successors and assigns.

                                      -3-
<PAGE>
 
          d.   This Agreement contains the entire agreement and understanding
between the parties hereto, and no modification hereof shall be binding unless
in writing and signed by the parties hereto.

          e.   The provisions of this Agreement shall be deemed severable, and
the invalidity or unenforceability of any provision shall not effect the
validity or enforceability of the other provisions hereof.

          f.   This Agreement is executed in, and it is the intention of the
parties hereto that it shall be governed by the law of the State of Michigan.

     IN WITNESS WHEREOF, CRC has caused this Agreement to be executed by a duly
authorized officer and Employee has duly executed this Agreement on the date and
year above written.


CONCENTRIC RESEARCH CORPORATION,        EMPLOYEE/CONTRACTOR:
a Florida Corporation


By:____________________________         ___________________________


Witness:_______________________

Witness:_______________________


                                      -4-
<PAGE>
 
                                   EXHIBIT B

                      Loaned Employee Letter of Agreement


Concentric Network Corporation
Critical Technologies Incorporated
c/o CNC

     Re:  Conditions of Employment While Performing Services
          Concentric Network Corporation


Dear __________:

     I have agreed, as of ____________, 1995, to accept an assignment to
Concentric Network Corporation ("CNC") to perform services for the Concentric
Network Corporation in the capacity of ____________. I understand that during
the period in which I am performing services for CNC, I will still be an active
full-time employee of Critical Technologies Incorporated ("CTI"). As such, I
will be entitled to receive and be subject to the CTI compensation, benefits,
and other Human Resources plans and programs. I will not be considered an
employee of CNC and I further agree that I will not make any claim of
entitlement to any compensation, benefits or other Human Resources plans and
programs of CNC, if any.

     I further agree that any intellectual property rights as defined in the
addendum to this employee loan letter of agreement, created, written, developed
or made by me while performing services for CNC shall be and shall continue to
be the property of CTI, as set forth in the addendum to this letter.

     I understand and agree that neither the provisions of my assignment to CNC
nor this Letter of Agreement constitute a contract of employment or set forth
employment terms between me and CTI. I understand that my employment
relationship with CTI is by mutual consent (employment at will) and that I have
the right at any time to terminate my employment for any reason. I also
understand that CTI reserves the right to terminate my employment on the same
basis.


                                        Sincerely,


                                        ________________________________________


                                     -5- 
<PAGE>
 
                                    EXHIBIT C

                         CONCENTRIC RESEARCH CORPORATION



                              CRC 1995 EXPANSION PLAN
<PAGE>
 
SCOPE - EXPANSION PLAN
- --------------------------------------------------------------------------------

MANAGE THE SUCCESSFUL IMPLEMENTATION OF THE 1995 NETWORK EXPANSION UPGRADES. 
PROVIDE THE BASIS FOR MANAGEMENT OF FUTURE NETWORK EXPANSION.

 .       Implement Xylogics terminal server technology
 .       Install V.34 technology
 .       Immediately bring all T1 facilities to full utilization
 .       Implement CMS diagnostic upgrade
 .       Create basic statistics document
 .       Ongoing capacity requirement (i.e. Affinity Programs)
 .       Create change control procedures



<PAGE>
 
OBJECTIVES - EXPANSION PLAN
- --------------------------------------------------------------------------------

 .       Formulate all current and future (1995) capacity data
 .       Model capacity data against current network provisioning
 .       Develop budget requirements
 .       Procure all hardware, software and services
 .       Manage the implementation and capacity upgrades
 .       Quality assurance testing
 .       Document process and solutions




<PAGE>
 
METHODOLOGY - EXPANSION PLAN
- --------------------------------------------------------------------------------

The Rapid Expansion of existing network facilities is possible due to the 
immediate availability of all required components.

        .       AT&T Frame-Relay services have been expanded to 600% of last 
                year's capacity. This allows for rapid acquisition of additional
                resources.

                .       Frame Ports
                .       Frame Circuits
                .       Frame Committed Information Rates

        .       Racal-Datacom product availability is excellent for the specific
                networking components required in the expansion plan.

        .       Networking Engineering and Operations personnel are well versed
                in the coordination of the required LEC facilities. POP
                locations are all currently provisioned with T1 facilities
                capable of immediate expansion.


<PAGE>
 
                         METHODOLOGY - EXPANSION PLAN
- --------------------------------------------------------------------------------

 . CRC and Vendor(s)                Organizational Chart
                                   Functional Responsibilities

 . Existing                         Statistics/Hardware
 . Future                              Documentation        Implementation
                                                                Plan
 . Network diagrams                    Define
 . Budget approval                  Requirements

 . Define management requirements      Define       
 . Document process and findings    Change Control
 . Quality Assurance review


<PAGE>
 
                    [This page intentionally left blank]
<PAGE>
 
METHODOLOGY - EXPANSION PLAN


 .       Deliver Requirements to Vendors         Hardware
                                                Procurement     Procedures 
                                                                Document

 .       Project Management                      Begin Phased
                                                Installation
                                                                Close Project

 .       Quality Assurance Review                Network
                                                Testing

 .       As Built Network Documentation          Network
                                                Documentation
<PAGE>
 
METHODOLOGY - EXPANSION PLAN

DEVELOP & DRIVE THE CAPACITY PLANNING METHODOLOGY AND PERFORM THE FOLLOWING 
ACTIVITIES TO ENSURE NETWORK PERFORMANCE.

 .       Define the hardware/ statistics report formatting
 .       Coordinating all activities with associated vendors
 .       Create change control procedures
 .       Define and document the detailed requirements
 .       Develop working design document
 .       Create detailed port cost contribution
 .       Manage to predictable implementation plan
 .       Provide detailed progress updates to mangement and the board as required
 .       Overall project management

This approach will ensure that ongoing requirements be handled in a timely,
cost effective manner insuring superior customer support.
<PAGE>
 
SCOPE - NETWORK EVOLUTION PLAN

 .       FINALIZE THE NETWORK RFP PROCESS AND WORKING NETWORK DESIGN. THIS 
        EFFORT WILL ENSURE COMPETITIVE COST STRUCTURES EXIST FOR THE NETWORK. 
        WHILE ENSURING HIGH CAPACITY, LOW LATENCY NETWORK PERFORMANCE

 .       Methodology and approach
 .       Vendor(s) selection
 .       Working network design
 .       Manage the implementation and migration
 .       Document process and solutions
<PAGE>
 

OBJECTIVES - NETWORK EVOLUTION PLAN


 .       Rapid completion of RFP process
 .       Provide a working network design that meets tactical and strategic 
        requirements
 .       Facilitate vendor "Proof Of Concept" against network design
 .       Define and analyze vendor pilot program(s)
 .       Implement final solution
<PAGE>
 
                    [This page intentionally left blank]
<PAGE>
 
METHODOLOGY - PHASE 1 NETWORK EVOLUTION PLAN

 .       Complete                        Requires 
                                        Document

 .       Complete                        Solicit
                                        Vendors
                                                        Select Finalists
 .       Complete                        Vendor
                                        Responses

 .       Define scoring criteria
 .       Determine selection committee   Vendor 
 .       Evaluate vendors                Scoring
 .       Document process and findings
 .       Quality assurance review
 .       Management update
<PAGE>
 
METHODOLOGY - PHASE 2 NETWORK EVOLUTION PLAN

 .       Develop design vision                   Finalists 
 .       Update detailed requirements            Requirements        Develop
 .       Present requirements to vendors                             Pilot Plan

 .       Joint working design                    Conceptual
                                                Designs             Pilot
                                                                  Solution(s)
 .       Vendor(s) proof of concept
 .       Vendor(s) presentations                 Vendor Proof
                                                of Concept           
                                                                    Evaluate
                                                                    Pilots
 .       Define scoring criteria
 .       Evaluate vendors                        Vendor
 .       Document process and findings           Scoring
 .       Quality assurance review
 .       Management update
                                                                   
<PAGE>
 
METHODOLOGY - NETWORK EVOLUTION PLAN

FINAL WORKING DESIGNS AND PROOF OF CONCEPT WILL ENCOMPASS DETAILS RELATED TO:

 .       Cost
 .       Functionality
 .       Reliability
 .       Performance
 .       Management Capabilities

This approach ensures that a working design can be implemented for a "Leading 
Edge" network solution prior to large financial commitments.
<PAGE>
 
METHODOLOGY - NETWORK EVOLUTION PLAN

MANAGE THE METHODOLOGY AND PERFORM THE FOLLOWING ACTIVITIES TO ENSURE ITS 
SUCCESS.

 .       Define the scoring matrix
 .       Manage the selection committee
 .       Document phased results
 .       Define and document the detailed requirements
 .       Develop working design document
 .       Define the pilot and facilitate vendor implementation
 .       Overall project management
<PAGE>
 
                                  EXHIBIT "D"

        Concentric Network Corporation and Critical Technologies, Inc.


                            PERFORMANCE OBJECTIVES


1.   Develop and establish the network control center in Critical's St. Louis
     facility.

2.   Design, build and implement the seven (7) Canadian POP sites.

3.   Rapidly harden the Bay City POP site.

4.   Rapidly bring live seventy-one (71) local markets utilizing the LA (Virtual
     Local Access) techniques.

5.   Develop and implement a plan to segregate the CNC host systems.

6.   Rapidly develop the Intuit Registration Server.

7.   Deploy a total of [*] local and virtual access ports at a
     targeted average cost/port of [*].

8.   Successfully demonstrate the new network architecture. Included in this
     demonstration will be the attainment of the following objectives:

     a)   A latency factor of not more than _______. (to be determined by
          2/10/96)

     b)   A through-put purport of _________. (to be determined by 2/10/96)

     c)   The ability to reconfigure inbound port on a call-by-call basis.

     d)   The ability to provide best-fit routing on the back bone network.

9.   Develop a field trial of a BRI ISDN connectivity.

10.  Develop a monthly network management report.

11.  Develop and implement on-line credit card authorization.

12.  Implement the Portal Back Office System or an equivalent next generation
     "back office system".

13.  Implement a proactive capacity management system that ensures we maintain a
     mutually agreeable target grade-of-service.

- -----------------
       [*]Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.
<PAGE>
 
                                  EXHIBIT E

                       CONCENTRIC RESEARCH CORPORATION

                                  PLAN FOR 

                             NETWORK OPERATIONS
<PAGE>
 
                             NETWORK OPERATIONS 
                              MISSION STATEMENT


                   Provide convenient and cost effective
                    operations of customer networks while
                   controlling the rising and hidden costs
                      of network management and support


                             [LOGO APPEARS HERE]
<PAGE>
 
[LOGO APPEARS HERE]
                                  OBJECTIVE

                  Pro-actively monitor and resolve network
                  conditions before they negatively affect
                                network users
<PAGE>
 
                             NETWORK OPERATIONS

SCOPE

        DEVICE MANAGEMENT                               PHYSICAL MANAGEMENT
 .       Logical & Physical                      .       Moves/Adds/Changes
 .       LAN & WAN
 .       Routers, Hubs, Servers
 .       Threshold Monitoring

        TROUBLESHOOTING                                 ADMINISTRATION
 .       Fault Detection                         .       Problem Management
 .       Event to Alarm                          .       Trouble Tickets
 .       Correlation                             .       Thresholds
 .       Impact Analysis                         .       Security
 .       Corrective Action                       .       Agents
                                                .       Backup

        ASSET MANAGEMENT
 .       Equipment Assignments
 .       Configuration Information
 .       Firmware & Software
<PAGE>
 
                             NETWORK OPERATIONS

SERVICES

 .       Continuous 7x24x365 day proactive network monitoring
 .       Problem determination, tracking and resolution
 .       Problem impact analysis
 .       Vendor dispatch and service performance monitoring
 .       System performance and availability reporting
 .       Equipment configuration and database management
 .       Coordination of network adds, deletes and changes
<PAGE>
 
                             NETWORK OPERATIONS

STAFF EXPERIENCE

 .       2-5 years experience in data communications
 .       Operations training on all network management systems
 .       Operations training on communications equipment
 .       Network troubleshooting and restoration procedural training
 .       General operation training to include; trouble ticketing, escalation
        procedures, vendor dispatch, report generation

[LOGO APPEARS HERE]
<PAGE>
 
                             NETWORK OPERATIONS

SENIOR SUPPORT STAFF

 .       Consists of trained and experienced technical specialists who assist 
        network operators with problem diagnosis on an exception basis.

 .       These specialists become involved in those problems requiring 
        engineering investigation or software reconfiguration
<PAGE>
 
                             NETWORK OPERATIONS

SENIOR SUPPORT EXPERIENCE

 .       5-15 years experience in data communications
 .       Broad experience in data communication concepts and curriculum
 .       Emphasis on product and system specialization

[LOGO APPEARS HERE]

<PAGE>
 
                             NETWORK OPERATIONS
[LOGO APPEARS HERE]

MONTHLY REPORTING:

 .       Network performance and availability
 .       Trouble tickets processed
 .       Network adds, changes and deletes
 .       Network failure trend analysis
 .       Vendor maintenance call performance
<PAGE>
 
                            ORGANIZATION OVERVIEW

                          [FLOWCHART APPEARS HERE]
<PAGE>
 
                                  EXHIBIT I

SCOPE

 .       SOFTWARE DEVELOPMENT MANAGEMENT
        
        .       Manage registration server development effort for Intuit
        .       Manage host system software upgrades required for escalating 
                subscriber base

                        -Business requirements
                        -Technical requirements
                        -General analysis and design
                        -Detailed analysis and design
                        -Coding
                        -Integration and QA testing
                        -Beta testing
                        -Implementation / Certification
<PAGE>
 
14.  Implement a proactive network management process that achieves an average
     time-to-response of less than ______ hours on urgent trouble tickets and
     less than ______ hours on priority trouble tickets.

                                      -2-
<PAGE>
 
EXHIBIT F

[not included]
<PAGE>
 
                                   EXHIBIT G
                                   ---------

                        CONCENTRIC NETWORK CORPORATION
                        ------------------------------

                               OPTION AGREEMENT
                               ----------------

     THIS OPTION AGREEMENT is entered into effective ____________, 19__, between
CONCENTRIC NETWORK CORPORATION, a Florida corporation (the "Company"), and
_________________________ (the "Optionee").

     WHEREAS, the Company and CRITICAL TECHNOLOGIES INCORPORATED ("CTI") are
parties to an Employee Services and Staffing Agreement (the "Employee
Agreement") pursuant to which, among other things, CTI has leased certain
employees to the Company and the Company has agreed to issue options to purchase
an aggregate of 900,000 shares of Common Stock of the Company ("Option Shares")
to certain employees of CTI which, pursuant to the Employee Agreement, will be
leased to the Company, and to certain other principals and employees of CTI and
to CTI; and

     WHEREAS, an aggregate of ________ of the Option Shares (the "Performance
Option Shares") are subject to forfeit in the event certain performance
objectives set forth in an exhibit to the Employee Agreement are not timely
achieved (the balance of an aggregate of ________ Option Shares are referred to
herein as "Regular Option Shares"); and

     WHEREAS, the Optionee is one of the persons selected by CTI to receive an
option pursuant to the Employee Agreement;

     NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the parties hereto do hereby agree as follows:

     1.        Grant of Option.  The Company hereby grants to the Optionee the
               ---------------                                                
right and option (the "Option") to purchase all or any part of the number of
Option Shares set forth below, at a purchase price of $.25 per share and on the
other terms and conditions herein set forth.

               Total number of Regular Option Shares:  _________

               Total number of Performance Option Shares:  _________

     2.        Dates When Option Exercisable.
               ----------------------------- 

          a.        Except as otherwise provided in paragraph 2(d), Options for
each of the Regular Option Shares and the Performance Option Shares (if any)
will vest and become exercisable ratably over twelve (12) months, at the end of
each month after the date hereof, with Options for one-twelfth (1/12) of the
shares subject to Option (rounded to the nearest whole share) becoming
exercisable at the end of each such month.
<PAGE>
 
          b.        Except as otherwise provided in paragraph 2(e) and paragraph
8, the Option shall expire, to the extent it has not already been exercised, at
the close of business on ____________, 2005 (the tenth (10th) anniversary of the
Employee Agreement) (the "Expiration Date").

          c.        Except as otherwise provided in paragraph 2(e), the Option
with respect to all Regular and Performance Option Shares not then vested will
automatically be assigned to CTI if the Optionee ceases to be an employee of CTI
prior to the time all Option Shares are vested hereunder. It is expressly
understood and agreed that nothing herein is intended or shall be construed as
an employment contract or as implying any obligation on the part of CTI or the
Company to continue the Optionee's employment for any period of time after the
date hereof.

          d.        Notwithstanding paragraph 2(a), the Option shall immediately
become exercisable in full upon the effective date of any merger or
consolidation of the Company with or into any other entity, at which time the
Option shall automatically become an Option on exercise to purchase, with
respect to each Option Share purchasable hereunder (whether vested or not)
immediately before the consolidation or merger becomes effective, the securities
or other consideration to which a holder of one share of Common Stock is
entitled in the consolidation or merger without any change in or payment in
addition to the Exercise Price in effect immediately prior to the merger or
consolidation. The Company shall take any necessary steps in connection with a
consolidation or merger to assure that the provisions of this Option shall
thereafter be applicable, as nearly as reasonably may be, to any securities or
other consideration so deliverable on exercise of this Option. The Company shall
not consolidate or merge unless, prior to consummation, the successor entity (if
other than the Company) assumes the obligations of this paragraph by written
instrument executed and mailed to the Optionee at the address of the Optionee on
the books of the Company.

          e.        Notwithstanding paragraphs 2(b) and 2(c), in the event of
(i) the death of the Optionee, or (ii) termination of the Optionee's employment
by reason of his or her disability or incapacity, then in any of such events the
Option may be exercised (but only to the extent it was exercisable by the
Optionee on the date of his or her death or of such termination of employment),
by the Optionee, or the Optionee's personal representative, conservator (if any)
or guardian (if any), respectively, in the manner set forth below, for a period
of twelve (12) months (but not later than the Expiration Date) after the date of
the Optionee's death or of such termination of employment.

     3.        Method of Exercising Option.  The Optionee (or representative as
               ---------------------------                                     
provided above) may exercise the Option hereby granted on one or more occasions
at his or her discretion, on each occasion for all or any part of the Option
Shares for which the Option is then exercisable, by each time delivering to the
main business office of the Company, addressed to the attention of its Chief
Executive Officer or Secretary, (i) a written notice stating his or her election
to exercise the Option and the number of Regular and Performance (if any) Option
Shares to be purchased, together with (ii) cash or check in full payment of the
purchase price of the Option Shares to be purchased plus the amount of any
Federal and state withholding taxes payable by the Company as a result of such
exercise.  The Option shall be deemed to be exercised only upon receipt of such
notice and payment


                                      -2-
<PAGE>
 
by the Chief Executive Officer or Secretary.  The Company will advise the
Optionee, upon the Optionee's reasonable prior request, of the required amount
of such taxes.

     4.        Non-Transferability of Option. The Option may be exercised only
               -----------------------------
by the Optionee or as otherwise provided above or by the Employee Agreement. The
rights granted by this Option may not be assigned, transferred, pledged or
hypothecated in any way, other than by will or by operation of law, and except
for automatic transfer to CTI pursuant to Section 2(c), above, and further
assignment by CTI, pursuant to the terms of the Employee Agreement. Such rights
shall not be subject to execution, attachment or similar process. In the event
of the bankruptcy of the Optionee, or in the event of any prohibited assignment,
transfer, pledge, hypothecation or other disposition of the Option, or the levy
of any execution, attachment or similar process upon the Option, the Option
shall automatically expire and shall be null and void. Notwithstanding the
foregoing, however, with prior notice to the Company the rights granted by this
Option may be transferred between the Optionee in his or her personal capacity
and the Optionee as trustee of a trust (A) of which the Optionee is both sole
trustee and sole beneficiary during his or her lifetime, and (B) all of which is
treated under subpart E of Part I of Subchapter J of Chapter 1 of Subtitle A of
the Internal Revenue Code of 1986, as amended, as owned by the Optionee.

     5.        Share Adjustments.  In the event of any stock dividend on,
               -----------------                                         
reclassification, split-up or combination of, or other change in, the Company's
Common Stock, then the number or kind of Option Shares shall be correspondingly
added to, reclassified, increased, diminished or changed proportionately,
without increase or decrease in the aggregate purchase price of all Option
Shares.

     6.        No Rights of Optionee as Shareholder. The Optionee shall have no
               ------------------------------------
rights respecting this Option or the Option Shares except as expressly set forth
herein or in the Employee Agreement; and the Optionee shall have no rights as a
shareholder with respect to any Option Shares until this Option has been duly
exercised as to such Option Shares in accordance with the terms hereof. The
grant of this Option shall not affect in any way the right or power of the
Company to make adjustments, reclassifications, reorganizations or changes of
its common stock or its capital or business structure, or to merge or to
consolidate, or to dissolve or liquidate, or to sell or transfer any or all of
its business or assets.

     7.        Securities Laws. Neither this Option nor any of the Option Shares
               ---------------                                            
have been registered under the Securities Act of 1933, as amended, or the
securities laws of any state, in reliance on exemptions from the registration
provisions thereof. By acceptance hereof, the Optionee acknowledges such fact
and agrees that, unless the Option Shares are so registered prior to exercise
hereof, this Option and any Option Shares will be held for investment and not
with a view to distribution or resale, and may not be made subject to a security
interest, pledged, hypothecated, or otherwise transferred without either an
effective registration statement under such Act and compliance with applicable
state securities laws, which may not be possible, or an opinion of legal counsel
satisfactory to the attorneys for the Company that such registration is not
required under such Act and that applicable state securities laws will not be
violated by such action; and the Optionee further agrees that the certificates
for such Option Shares shall bear a legend substantially to such effect.

                                      -3-
<PAGE>
 
     8.        Performance Option Termination and Repurchase Provisions.  If
               --------------------------------------------------------     
performance objectives set forth in Exhibit E to the Employee Agreement have not
been achieved within twelve (12) months after the date of the Employee
Agreement, the Option for Performance Option Shares shall automatically
terminate and no longer be exercisable and the Company shall repurchase from the
Optionee at the purchase price of $.25 per share all Performance Option Shares
theretofore purchased by the Optionee upon partial exercise of this Option.

     9.        General.  The Company shall at all times during the term of the
               -------                                                        
Option reserve and keep available a number of shares of common stock equal to
the number of Option Shares, and shall pay all original issue and transfer taxes
with respect to the issue of Option Shares pursuant hereto and all other fees
and expenses necessarily incurred by the Company incurred in connection
therewith.


     IN WITNESS WHEREOF, the Company and the Optionee have executed this Option
Agreement as of the date first above written.


                                Company:  CONCENTRIC NETWORK CORPORATION



                                          By:___________________________________
                                             President



                                Optionee: ______________________________________


                                      -4-
<PAGE>
 
                                   EXHIBIT H

                         Colocation Services Agreement

This Colocation Services Agreement between Critical Technologies, a Missouri
corporation with principal offices at 1300 Baur Blvd., St. Louis, Missouri 83132
(hereinafter referred to as "Critical"), and Concentric Research Corporation
(hereinafter referred to as "CRC") with offices located 400 Forty first Street,
Bay City, Michigan 48708, is entered into this 1st day of November, 1994.

WHEREAS, Critical is a provider of colocation services; and

WHEREAS, CRC desires to engage Critical to provide colocation services as
described herein; and

WHEREAS, Critical desires to accept such engagement upon the terms and
conditions set forth herein.

NOW THEREFORE, in consideration of the mutual promises herein contained and
other good and valuable consideration, the receipt of which is hereby
acknowledged, CRC and Critical agree as follows:

I.   DEFINITIONS
     -----------

     a.   Colocation sites ("Sites")

          Physical space which shall have the characteristics specified on
          Appendix A, and shall be fit for the purposes of containing the Racks
          and Equipment, as hereinafter defined, in an environment that will
          enable the Racks and Equipment to operate according to Racal-Data Com,
          Inc. specifications.

     b.   Optimum Locations

          Optimum Locations shall be geographic locations (within which a Site
          may be selected) which locations shall be identified by Critical as
          most closely matching the criteria provided by CRC from time to time
          for purposes of Modeling and in the Optimum Location Requests, as
          provided in Article V of this Agreement. In identifying Optimum
          Locations, Critical shall consider:

          1.   which metropolitan areas have the greatest potential customer
               base

          2.   the determination of which physical location provides the
               greatest number of callers with a local dial-access number

          3.   conclusions or indications from Modeling based upon CRC's
               expressed criteria.
<PAGE>
 
          Critical shall provide a mathematical justification for each Optimum
          Location to CRC, which mathematical justification shall be approved by
          CRC.

     c.   Modeling services ("Modeling")

          The creation of a mathematical model built and maintained by Critical
          which shall enable Critical to recommend to CRC and CRC to select
          Optimum Locations pursuant to the criteria submitted by CRC. The Model
          shall incorporate data, including but not limited to; CRC's research
          in the desired markets and/or market places, the existing 800 number
          service network traffic data ordered geographically, and existing
          point of presence Site network traffic data.

     d.   Colocation services ("Services")

          The services being offered to CRC by Critical shall consist of
          Modeling, locating, qualifying and providing Optimum Locations and
          Sites, pursuant to Optimum Location Requests and Site Orders as
          described in Article V of this Agreement, providing supervision for
          any and all construction necessary at the Sites, accommodating
          installation of Equipment and Racks as hereinafter defined, insuring
          compliance with all codes, ordinances, rules and regulations,
          providing consolidated billing for the Sites. Critical shall provide
          communication with respect to the Services with the TM as hereinafter
          defined.

     e.   Industrial Telecommunications Racks ("Racks")

          The industrial telecommunication Racks which contain the Equipment, as
          hereinafter defined, including but not limited to:

          Excal Rackmounts
          ALM 2332 Rackmounts
          INX Rackmount Shelves

     f.   Colocation equipment ("Equipment")

          All of the Equipment, other than Racks, owned by Racal and leased to
          CRC which are located at the Sites, which Equipment includes but is
          not limited to that type described on Appendix B.

     g.   Racal-Data Com, Inc. ("Racal")

          A Florida corporation with principal offices located at 1601 North
          Harrison Parkway, Sunrise, Florida 33323-2899, which is the owner of
          all or part of the Equipment and Racks and leases those Equipment and
          Racks to CRC.

                                      -2-
<PAGE>
 
     h.   Primary Entity

          Any entity through which Critical leases or otherwise holds an estate
          in the Site.

     i.   CRC Telecommunications Manager (the "TM")

          CRC shall designate a single employee as its telecommunication manager
          for purposes of this Agreement and as a primary CRC contact for
          Critical with respect to this Agreement. The TM shall be designated by
          CRC, in writing, upon execution of this Agreement and Critical shall
          be notified, in writing within 48 hours, in the event that CRC
          appoints a new TM.

II.  AFFIRMATION
     -----------

     Critical shall provide Services, Optimum Locations and Sites pursuant to
     Orders (as defined in Article V) to CRC.

III. TERM OF AGREEMENT
     -----------------

     This Agreement shall be effective upon the date first written above
     ("Effective Date") and shall continue for a period of twenty-four (24)
     months from the Effective Date. Thereafter, this Agreement shall
     automatically renew itself in twelve (12) month increments unless either
     party notifies the other of its decision to terminate this Agreement by
     providing the other party with sixty (60) days written notice prior to the
     expiration of the period then in effect ("Renewal Period"). This Agreement
     shall govern all Orders for Services which are received by Critical within
     twenty-four (24) months from the Effective Date or any Renewal Period.
     Notwithstanding anything contained herein, in the event that CRC shall fail
     to renew after the first twenty-four (24) months of the Agreement, and in
     the further event CRC shall have ordered more than 100 Sites which are
     subject to this Agreement ("Additional Sites"), CRC shall pay the sum of 
     [*] for each Additional Site for each month less than twenty-four (24)
     months which has expired from the time the Additional Site was ordered to
     the date of termination of the Agreement under this paragraph.




IV.  PAYMENT FOR SERVICES AND COMMENCEMENT
     -------------------------------------

     CRC shall pay to Critical the sum of [*] per Site per month, for the first
     Rack, and [*] for each additional Rack at each Site, per month, up to a
     total of three (3) Racks. With respect to the first Order, billing shall
     commence on October 15, 1994. In addition, with respect to the first order,
     CRC shall pay the sum of [*] upon execution of this Agreement. Thereafter,

- ---------------------

     [*] Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commisssion.  Confidential treatment has been
requested with respect to the omitted portions.

                                      -3-
<PAGE>
 
     commencement of billing for each Site shall begin upon execution of the
     Site Order as provided in Article V of this Agreement (hereinafter referred
     to as the "Commencement Date"). Payments are due monthly, on the first day
     of each calendar month. If the Commencement Date of each Site or additional
     Rack is other than the first day of each month, the first payment due
     hereunder shall be equal to one-thirtieth (1/30) of the monthly rate set
     forth for each day from and including the Commencement Date through and
     including the last day of the month prior to the beginning of the term and
     the monthly rate for the full initial month. Certain of the Sites shall be
     located at Racal property or leaseholds ("Racal Sites") and CRC may elect
     to obtain Sites. Notwithstanding anything else contained within this
     Article IV, CRC shall only be required to pay the sum of [*] per month
     per site for Racal Sites or where the site is obtained by CRC. In the event
     that number of Sites subject to this Agreement shall drop below 90 Sites,
     then CRC shall be required to pay the sum of [*] per month per Site for
     Racal Sites or where the Site is obtained by CRC.

V.   ORDERING PROCEDURE
     ------------------

     a.   Optimum Location Request

          CRC, acting through the TM, shall make a written request to Critical
          to identify Optimum Locations from time to time in order to enable CRC
          and Critical to select new Sites or move existing Sites.

          1.   The TM shall identify the number of Optimum Locations which it
               desires Critical to identify.

          2.   The TM shall further specify the number of days, but not less
               than 30 days, within which CRC expects Critical to provide a
               written response ("Identification Period").

               (i)    In the event that Critical is unable to respond within the
                      Identification Period, it shall notify the TM, before the
                      expiration of 75 percent of the respective Identification
                      Period, that it will be unable to comply within the
                      Identification Period. CRC may then elect to cancel the
                      Optimum Location Request or issue an amendment to the
                      Request to provide a new Identification Period.

     b.   Site Order

          The TM shall, from time to time, direct Critical, in writing, to
          identify a Site within an Optimum Location. The TM shall further
          specify the number of days, but not less than thirty days unless
          agreed in writing between the parties, within which CRC expects
          Critical to provide a Site Order ("Order Period").


                                      -4-

- ------------------
    [*] Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.






<PAGE>
 
          1.   In the event that Critical is unable to respond within the Order
               Period it shall notify the TM, before the expiration of 75% of
               the respective Order Period, that it will be unable to comply
               with the Order Period. CRC may then elect to cancel the Site
               Order or issue an amendment to the Site Order to provide a new
               Order Period.

          2.   Upon identification of a Site by Critical, Critical shall prepare
               a Site Order with the address of the Site and deliver the Site
               Order to the TM. The TM shall execute the Site Order on behalf of
               CRC, confirming the Site Order.

               (i)    Subsequent to the execution of a Site Order, Critical
                      shall deliver to the TM, in electronic form, a list of all
                      exchanges which are a local call to the exchange from the
                      Site.

               (ii)   Subsequent to the execution of the Site Order by the TM,
                      if CRC ships Racks or Equipment to the address on the Site
                      Order or incurs any charges, including AT&T or local
                      exchange carrier charges, and the address on the Site
                      Order is incorrect or the Site cannot be used, for any
                      reason which is not the fault of CRC or Racal, Critical
                      shall be liable for all expenses incurred or related to
                      the Site address being incorrect or the Site not being
                      available for use by CRC, including Equipment and Cabinet
                      shipment charges.

     c.   Replacement Site

          In the event that a Site Order is made, and after not less than 120
          days subsequent thereto, CRC determines that the Site does not meet
          its marketing criteria ("Nonconforming Site"), CRC may terminate the
          Nonconforming Site and order a Replacement Site unless the Site is
          selected by CRC without Critical's advice.

          1.   The Replacement Site must be leased for the balance of the term
               of the Nonconforming Site.

          2.   The Replacement Order procedure shall be as follows:

               (i)    The TM shall, in writing, request a Replacement Site,
                      identifying the Nonconforming Site, and specifying a new
                      Optimum Location. The TM shall further specify the Order
                      Period. The term of this Order Period in such event shall
                      not be less than 30 days.

               (ii)   In the event that Critical is unable to respond within the
                      Order Period it shall notify the TM before the expiration
                      of 75% of the respective Order Period, that it will be
                      unable to comply with the Order Period.

                                      -5-
<PAGE>
 
                      CRC may then elect to cancel the Replacement Order or
                      issue an amendment to the Replacement Order to provide a
                      new Order Period.

               (iii)  Upon indemnification of a Replacement Site by Critical,
                      Critical shall prepare a Replacement Order with the
                      address of the Replacement Site and deliver the
                      Replacement Site Order to the TM. The TM shall execute the
                      Replacement Site Order on behalf of CRC confirming the
                      Replacement Site Order.

                      1)  Subsequent to the execution of a Replacement Site
                          Order, Critical shall deliver to the TM, in electronic
                          form, a list of all exchanges which are a local call
                          to the exchange of the Site.

                      2)  Subsequent to the execution of the Replacement Site
                          Order by the TM, if CRC ships Racks or Equipment to
                          the address on the Replacement Site Order or incurs
                          any charges, including AT&T or local exchange carrier
                          charges, and the address on the Replacement Site Order
                          is incorrect or the Site cannot be used, for any
                          reason which is not the fault of CRC or Racal,
                          Critical shall be liable for all expenses incurred or
                          related to the Site address being incorrect or the
                          Site not being available for use by CRC, including
                          Equipment and Cabinet shipment charges.

VI.  WARRANTY
     --------

     Critical warrants that the Services shall be provided to the best of its
     ability, skill and knowledge. Critical further warrants that the Sites will
     meet the requirements set forth on Appendix A and that the Services will be
     of the kind and quality and fulfill the purposes defined in Article I of
     this Agreement and will be performed by qualified personnel. Critical
     warrants to CRC peaceful possession of all of the Sites. THE FOREGOING
     WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES EXPRESS, IMPLIED, OR STATUTORY,
     INCLUDING WARRANTY OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     AND NO REPRESENTATIVE OF CRITICAL IS AUTHORIZED TO ALTER OR ENLARGE THIS
     WARRANTY.

VII. INSURANCE
     ---------

     Critical shall maintain in force during the term of this Agreement a policy
     of insurance issued by a company authorized to engage in the insurance
     business in all of the states in which the Sites are located. The policy
     shall insure the Racks and Equipment against the perils of fire, extended
     coverage, vandalism, malicious mischief, special extended coverage ("All
     Risk"), and sprinkler coverage. Further, Critical shall provide a
     comprehensive general liability insurance policy insuring CRC against any
     liability arising out of the use, occupancy or maintenance of the Site and
     all access areas appurtenant thereto. Each policy shall be on an occurrence
     basis

                                      -6-
<PAGE>
 
      and shall insure not less than Three Million Dollars ($3,000,000.00) per
      occurrence. The insurance policy shall insure the hazards of the Site and
      operations conducted in and on the Site, independent contractors,
      contractual liability, and shall name CRC and Racal as insured parties.
      CRC shall be furnished with a copy of the certificate of insurance.

VIII. FORCE MAJEURE
      -------------

      Neither Critical or CRC shall be considered in default in performance of
      their obligations hereunder if performance of such obligations is
      prevented or delayed by acts of God or government, labor disputes, failure
      or delay of transportation, or by vendors or subcontractors, or any other
      similar cause or causes beyond the reasonable control of either party.
      Time of performance of either party's obligations hereunder shall be
      extended by the time period reasonably necessary to overcome the effects
      of such force majeure occurrences.

IX.   CASUALTY
      --------

      In the event that a Site shall be destroyed or rendered unusable by fire
      or other casualty, Critical shall have 30 days to relocate the Site.

X.    TITLE AND LOCATION
      ------------------

      Nothing contained herein shall give or convey to Critical any right, title
      or interest in or to any of the Racks or Equipment, and Critical
      represents and agrees that it shall furnish to CRC such documentation as
      CRC requires to confirm said title in CRC or Racal.

      Critical shall notify all Primary Entities of the interest of Racal and
      CRC in the Racks and Equipment. Further, Critical shall file, on behalf of
      CRC and Racal, a UCC financing statement in each respective state where a
      Site is being provided pursuant to this Agreement, Critical shall provide
      to CRC the names and addresses of the Primary Entities and CRC shall
      prepare the UCC financing statements, Critical shall obtain the signatures
      of the Primary Entities and file the UCC financing statements in the
      appropriate state offices. CRC shall pay all filing fees. Each UCC
      financing statement shall identify the Primary Entity with respect to the
      Site, address of the Primary Entity, the identity of Racal and/or CRC as
      the owners of the Racks or Equipment. The UCC shall be in a form which CRC
      deems advisable to secure the interests of CRC and Racal. Without limiting
      the foregoing, Critical shall obtain the signature of each of the Primary
      entities on one or more financing statements in a form and substance
      satisfactory to CRC covering all of the Racks and Equipment to be located
      at the Sites pursuant to this Agreement.

XI.   OWNERSHIP RIGHTS
      ----------------

      a.  Racks and Equipment

                                      -7-
<PAGE>
 
          The Racks and Equipment shall at all times remain the property of CRC
          and/or Racal. Critical agrees that it shall allow the Equipment and
          Rack to be labeled as property of CRC and Racal. Critical shall
          replace any such stenciling tag or plate which may be removed or
          destroyed or become illegible. Critical shall keep all Racks and
          Equipment free from any marking or labeling which might be interpreted
          as a claim of ownership thereof by Critical or any Primary Entity, or
          might be interpreted as a claim of anyone so claiming through Critical
          or any Primary Entity.

          1.   Upon termination or expiration of this Agreement, Critical shall
               provide immediate access to the Sites to remove all Equipment and
               Racks.

     b.   Modeling

          With respect to the Modeling, Critical shall retain ownership of the
          analytical process. CRC shall retain ownership of all data provided
          for the Modeling and all results of the application of the analytical
          process to the data. Critical shall not, without prior written
          permission of CRC, transfer, disclose or otherwise provide the data or
          results of the Modeling to any person outside of Critical. Critical
          agrees that it shall thoroughly safeguard the confidentiality of the
          data in the Modeling results, and in no event shall it be to a lesser
          extent than Critical safeguards its own proprietary information.
          Critical agrees that access to such data and the Modeling results will
          be given only to employees of Critical who require access in the
          course of Critical's business, and such employees will be informed of
          the confidential nature thereof and shall be required to observe
          provisions of confidence as set forth herein.

          1.   Within seven days following termination or expiration of this
               Agreement, Critical shall return all data provided by CRC for the
               Modeling and all Modeling results. Thereafter, within said seven
               day period, Critical shall destroy all copies of the Modeling
               Data provided by CRC and the Modeling results which Critical has
               in its possession.

XII. DEFAULT
     -------

     a.   By CRC:
          -------

          1.   An Event of Default by CRC shall occur hereunder if: (i) CRC
               fails to make payments as defined herein or to perform any other
               condition of this Agreement, which shall continue for a period
               thirty (30) business days following written notice thereof, (ii)
               CRC fails within forty-five (45) days after the commencement of
               any proceeding against CRC seeking any reorganization
               arrangement, composition, readjustment, liquidation, dissolution,
               or similar relief under any present or future statute, law,
               regulation, to obtain the dismissal of such proceeding or (iii)
               if a trustee or receiver is appointed or liquidation proceedings
               are initiated with respect to all or a substantial portion

                                      -8-
<PAGE>
 
               of the properties of CRC, without the consent of Critical, and
               CRC is unable to vacate such appointment within forty-five (45)
               days.

      b.  By Critical:
          ------------

          1.   An Event of Default by Critical shall occur hereunder if: (i)
               Critical fails to provide Services as defined in Article I or
               Sites as set forth in Appendix A for reasons other than force
               majeure, or the acts or omission of CRC, or fails to perform any
               other covenant or condition of this Agreement, and Critical is
               unable to cure or remedy any such deficiency within thirty (30)
               business days following receipt of written notice of such
               deficiency by CRC, (ii) Critical fails within forty-five (45)
               days after the commencement of any proceeding against Critical
               seeking any reorganization arrangement, composition,
               readjustment, liquidation, dissolution, or similar relief under
               any present or future statute, law, regulation, to obtain the
               dismissal of such proceeding or, (iii) if a trustee or receiver
               is appointed or liquidation proceedings are initiated with
               respect to all or a substantial portion of the properties of
               Critical, without the consent of CRC, and Critical is unable to
               vacate such appointment within forty-five (45) days.

XIII. SITE CASUALTY
      -------------

      CRC shall use its best efforts to maintain a minimum of 80 sites subject
      to this Agreement.

XIV.  REMEDY IN THE EVENT OF DEFAULT
      ------------------------------

      a.  By CRC:
          -------

          Upon the occurrence of an Event of Default or in case of breach by
          CRC, Critical may cancel this Agreement, declare the entire amount of
          any unpaid balance due under this Agreement due and payable, and use
          all available remedies to remove CRC and its Racks and Equipment from
          possession of the Sites by ejectment or otherwise. This remedy of
          Critical is in addition to all other remedies at law or in equity.

      b.  By Critical:
          ------------

          Upon the occurrence of an Event of Default by Critical, CRC may:

          1.   Terminate this Agreement without further liability; and

               (i)    exercise any other right or remedy which may be available
                      at law or in equity;

                                      -9-
<PAGE>
 
               (ii)   elect, in its sole discretion, to retain possession of all
                      or a part of the Sites, on the condition that it assumes
                      Critical's lease obligations with the Primary Entity for
                      each respective Site that CRC retains possession of.
                      Critical may seek compensation in a court of law for any
                      leases not assumed by CRC.

XV.    ASSIGNMENT
       ----------

       a. By Critical:
          ------------

          Any assignment of this Agreement by Critical without the written
          consent of CRC shall be void, such consent shall not be unnecessarily
          withheld.

       b. By CRC:
          -------

          CRC shall not assign this Agreement, except to Racal, without first
          obtaining the written consent of Critical, which consent will not be
          unreasonably withheld, conditioned, or delayed. Critical's consent
          shall be conditioned on Critical's approval of the economic viability
          of the proposed assignee.

          Notwithstanding anything to the contrary contained herein, any
          transfer of this Agreement from CRC by merger, consolidation or
          liquidation or any change in the ownership or power to both the
          majority of the outstanding stock of CRC shall not constitute an
          assignment for the purposes of this section.

XVI.   GOVERNING LAW: FORM
       -------------------

       This Agreement shall be governed and construed in accordance with the
       laws of the State of Michigan. The parties hereby consent and submit the
       exclusive jurisdiction of the appropriate state or federal court serving
       Bay County, Michigan, as to any dispute or controversy arising either
       directly or indirectly, under or in connection with this Agreement.

XVII.  WAIVER
       ------

       No waiver by either party of any default shall operate as a waiver of any
       other default or of the same default on a future occasion. No delay,
       course of dealing or omission on the part of either party in exercising
       any right or remedy shall operate as a waiver thereof, and no single or
       partial exercise by either party of any right or remedy shall preclude
       any other or further exercise thereof or the exercise of any other right
       or remedy.

XVIII. SEVERABILITY
       ------------

       If any provision or provisions of this Agreement shall be held to be
       invalid, illegal or unenforceable, the validity, legality and
       enforceability of the remaining provisions shall not in

                                     -10-
<PAGE>
 
     any way be affected or impaired thereby, provided such provision still
     expresses the intent of the parties. If the intent of the parties cannot be
     preserved, the Agreement shall either be renegotiated or rendered null and
     void.

XIX. NOTICES
     -------

     Any notices or communications given or required under this Agreement shall
     be sufficiently given if delivered personally, in writing or sent by telex
     or facsimile, federal express, registered or certified mail, postage
     prepaid, to the other party at the following address:

     TO:  Critical Technologies

          ---------------------
          St. Louis, MO 
                        -------
          Attn:

          Timothy R. Huff
          131 Jefferson Street
          Charleston, MO 63301

     TO:  Concentric Research Corporation
          400 Forty First Street
          Bay City, MI 48708
          Attn: President

          With a copy to:
 
          Susan M. Cook
          Lambert, Leser, Cook, Schmidt & Giunta, P.C.
          309 Davidson Building, P.O. Box 835
          Bay City, MI 48707-0835

     Such notice or other communications shall be deemed received (a) on the
date delivered, if delivered personally; or (b) upon receipt, if sent by telex
or facsimile, federal express or (c) three (3) business days after being sent,
if sent registered or certified mail.

XX.  ENTIRE AGREEMENT
     ----------------

     The terms and conditions contained in this Agreement, and the referenced
                                                           ------------------
     Addendums which are hereby incorporated herein, shall be applicable to all
     ----------------------------------------------
     Optimum Location Requests and Site Orders during the effectiveness of this
     Agreement whether referenced in same or not. This Agreement expresses the
     entire understanding and agreement of the parties with reference to the
     subject matter hereof, and is a complete and exclusive statement of the
     terms of this Agreement, and no representations or agreements modifying or
     supplementing the terms of

                                     -11-
<PAGE>
 
     this Agreement shall be valid unless in writing, signed by persons
     authorized to sign agreements on behalf of both parties.

                                     -12-
<PAGE>
 
     IN WITNESS THEREOF, this Agreement was entered into as of the day and year
first written above.

                              CRITICAL TECHNOLOGIES


                              BY:  /s/ James F. Crowe
                                   -------------------------------

                              ITS:  President, as President
                                    ------------------------------

                              DATE:  November 1, 1994
                                     -----------------------------


                              CONCENTRIC RESEARCH CORPORATION

                              BY:  /s/ Donald I. Schutt
                                   -------------------------------

                              ITS:  Chief Operating Officer
                                    ------------------------------

                              DATE:  November 1, 1994
                                     -----------------------------

                                     -13-
<PAGE>
 
                                    APPENDIX


A.   Electrical

     1.   One 30 Amp 120 Volt Single phase dedicated circuit with MEMA space LB-
     30R for each communication equipment rack. Additional circuits required for
     an independent air conditioning unit should the site's air conditioning be
     turned off for any amount of time.

     2.   The service must by 24 hours per day, seven days a week, every day of
     the year without interruption.

B.   Physical space

     1.   Each telecommunications rack needs 24" width, 26" depth, 6' height.

     2.   Each telecommunications rack shall have 2' front and rear access at
     all times.

     3.   Each telecommunications rack requires at least 1' clearance between
     the interior ceiling and the top of the rack.

     4.   Each closet shall have a 4' x 4'3/4" plywood backboard (or equivalent
     as per the Local Exchange Carrier's specifications) painted black to be
     within 5' of the telecommunications rack(s).

C.   Environment

     1.   Air conditioning is a requirement for all telecommunications racks and
     should be on at all times.

     2.   The operating environment shall comply with all environmental
     specifications as published in Racal's technical documentation.

     3.   There shall be suitable electrical lighting as required for service.

     4.   There shall be a key entry lock on the cabinet door to restrict access
     to the cabinet. 


D.   Access

     1.   Access to the telecommunications closet shall be provided on a 7 day a
     week 24 hour a day basis all days of the year.
<PAGE>
 
     2.   Access to the telecommunications closet shall be provided to (a) CRC
     authorized personnel (b) Racal authorized personnel and (c) Local Exchange
     Carrier personnel within 4 hours of notification.

     ANY CHANGES REQUIRING OR PERTAINING TO INSIDE WIRING, WHETHER REQUESTED OR
     DIRECTED BY A LOCAL EXCHANGE CARRIER OR OTHERWISE, SHALL BE THE
     RESPONSIBILITY OF CRITICAL TECHNOLOGIES.


                                      -2-
<PAGE>
 
EXHIBIT I


Scope
- ------

 . Software Development Management
  . Manage registration development for Intrust
  . Manage host system software upgrade required for escalating subscriber base

    - Business requirements
    - Technical requirements
    - General Analysis and design
    - Coding
    - Integration and testing
    - Beta testing
    - Implementation testing

<PAGE>
 
                                   SCHEDULE 1

                  to Employee Services and Staffing Agreement
                Dated as of the _____ day of _____________, 1995
           by and between Concentric Network Corporation ("CNC") and
          Critical Technologies Incorporated ("CTI") (the "Agreement")

     The following provisions dealing with Share Options (as defined in the
Agreement) shall be deemed part of the Agreement as if fully set forth therein.

     1.   Compliance with SEC Rule 504.  CNC agrees that it will take all
          ----------------------------                                   
reasonable steps to comply with Rule 504 of Regulation D ("Regulation D")
promulgated by the Securities and Exchange Commission ("SEC") under the
Securities Act of 1933 (the "Act") so long as CNC is not subject to the
reporting requirements of Section 13 or 15(d) of the Securities Exchange Act of
1934 (the "Exchange Act").  These steps will include, but not be limited to:

          a.   CNC will timely file a notice on Form D with the SEC.

          b.   CNC will, on an ongoing basis, provide to holders of Options
     financial and other information concerning CNC reasonably necessary to
     enable holders of Options to make fully informed decisions concerning
     exercise of their Options and investment in shares of CNC Common Stock
     ("Shares").

     2.   At such time as CNC becomes subject to the reporting requirements of
Section 13 or 15(d) of the Exchange Act, CNC shall:

          a.   Register with the SEC on Form S-8 those Options and Shares
     subject to Options held by leased employees hereunder or other principals
     or employees of CTI who are advisors or consultants to CNC;
<PAGE>
 
          b.   take all steps reasonably necessary to comply with Rule 505 of
     Regulation D with respect to Options and Shares subject to Options held by
     persons who are not leased employees hereunder or otherwise advisors or
     consultants to CNC. Such compliance will include providing to such Option
     holders on a timely basis copies of all reports and proxy materials filed
     by CNC with the SEC, all Annual Reports and other materials provided by CNC
     generally to its shareholders, and any other information reasonably
     necessary to comply with the information requirements of Rules 502 and 505
     of Regulation D.

     3.   "Piggy-Back" Registration Rights.  If, prior to the second anniversary
          --------------------------------                                      
of the date on which CNC becomes subject to the reporting requirements of
Section 13 or 15(d) of the Exchange Act, CNC files with the SEC a Registration
Statement to register Shares under the Act (other than a Registration Statement
on Form S-4 or S-8), holders of Shares purchased upon exercise of Options which
Shares have, at the time of filing of such Registration Statement, been held for
less than two years and are "restricted securities" (as defined in Rule 144
promulgated by the SEC), shall be given the right to include such Shares in
CNC's Registration Statement and sell such Shares in the offering made pursuant
to such Registration Statement ("Registration Rights") on substantially the
following terms:

          a.   CNC will bear the expenses of registration of such Shares other
     than underwriters' discounts and commissions with respect thereto, and fees
     and expenses of counsel to the selling shareholders.

          b.   Such selling shareholders will execute the Underwriting Agreement
     pursuant to which Shares are sold in the registered offering, which
     Underwriting Agreement may contain indemnification and other provisions in
     substantially the form normally contained in such agreements.

                                      -2-
<PAGE>
 
          c.   The Registration Rights will be available only with respect to
     the number of Shares the underwriters indicate, in their judgment, will not
     adversely impact the registered offering.

                                      -3-
<PAGE>
 
September 30, 1996

Mr. Mike Anthofer
Vice President & CFO
Concentric Network Corp.
10590 N. Tantau
Cupertino, California 95014

                                                          C R I T I C A L
                                                            TECHNOLOGIES
Fax No. 408-342-2876                                  I N C O R P O R A T E D


Dear Mike:

Below I have outlined the changes to our agreement.  Please indicate your
concurrence with these modifications by signing below.  The specific changes for
our "Employee Service and Staffing Agreement" are:

1)    Delete paragraph 1d, subsections 4 and 5.

2)    Waive the notice of an extension in paragraph 2.0 and extend the agreement
      for an additional two (2) years (October 31, 1999).

3)    Change section 4f (second paragraph) so that the upcharge Is changed to
      [*] instead of [*] for staff positions currently on board as of the
      signing of the agreement (see attached listing). Change the upcharge to be
      only on base salaries, payroll taxes and benefits. Other expenses
      associated with hiring will be passed through at cost. Said taxes and
      benefits are currently billed at [*] of base salaries; therefore, the
      total markup over base salaries is [*]. Additional hiring over those
      positions noted on the attached list will be at a [*] upcharge or
      currently [*] over base salaries. Additionally, CNC commits to a
      minimum level of staffing equal to the staffing level as of the date of
      signing of this document.

4)    Delete paragraph 6(a).

5)    Delete 8(a)(4) and change 8(a)(3) so that said fees are no longer due
      unless sites are added after Installation of the super POPs currently
      scheduled.

6)    As a consideration of this agreement, the CNC board must agree that all
      "performance shares" or options have been earned (see attached
      "Performance Summary"). Said options and all other

- --------------------------

      [*] Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.
<PAGE>
 
      options under the original agreement to be granted and delivered within 10
      days of the first board meeting following the signing of this agreement.
      Additionally, CNC shall provide an option agreement acceptable to CTI with
      which an option holder may execute such options. Said option agreement to
      be provided within 10 days of the board meeting following the signing of
      this agreement. Failure of the CNC board to approve these two items will
      nullify this agreement.

7)    It is agreed that paragraph 10 of the existing contract shall provide that
      CTI shall have the right to assign or transfer their duties, obligations
      and all benefits under the contract to a merger or acquiring entity so
      long as that entity is not Netcom, PSI, UUNET, ANS, ATT Worldcom, MFB,
      GTE, Ameritech, PAC Bell, SBC, US West, NYNEX, BellSouth, Bell Atlantic,
      Sprint Internet/Intranet Services, MCI Internet/Intranet Services, and
      CompuServe Network Services. Should CTI be acquired by one of the named
      competitors, CNC may at Its option exercise the "buy out option" and pay
      CTI a cash payment equal to [*] of the remaining value (an a present
      value basis at prime) of its profit and any unpaid relocation expenses
      (see "e" below). Said option to be exercised with ninety (90) days of
      notice by CTI of intention to merge with a competitor of CNC.

8)    CTI further agrees to limit access to CNC proprietary information to only
      those CTI employees who have a need to know.

9)    In order to provide an orderly transition at the end of the agreement, CTI
      agrees to locate all personnel and resources used to support CNC to a new
      subsidiary and transfer that entity to CNC according to the following
      plan:

      a.    CTI will create a wholly owned subsidiary. CTI will transfer all
            existing CNC staff to this entity. Additionally, all new CNC related
            staff will be hired by this subsidiary for those CNC operations
            housed in St. Louis, Missouri.

      b.    CTI will transfer its rights (including leasehold improvements)
            under Its lease to 3324 Hollenberg Drive to this new subsidiary.
            Said lease to have at least five (5 years remaining at the
            termination of this agreement at a cost not to exceed [*] per
            square foot (triple net). Any office equipment currently owned by
            CTI and used exclusively by the subsidiary employees will also be
            transferred. Additional office equipment for current or future
            employees of the subsidiary will be paid for by CNC and remain their
            assets.

      c.    CTI will transfer a nonexclusive license to its software for network
            modeling, site management. and telco reconciliation to this new
            entity.

- -------------------------

     [*]Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.
<PAGE>
 
      d.    CNC shall acquire title to this new subsidiary at the and of this
            agreement and CTI will vacate the promise on 3324 Hollenberg Drive.
            Both parties agree to execute such documents as may be necessary to
            minimize the tax effect to both entities.

      e.    CNC shall pay CTI [*] for relocation expense and the assets of
            the new subsidiary. This amount will be paid for costs as needed by
            CTI to relocate its other business to other facilities. CTI will
            provide to CNC on at least a quarterly basis their projected needs
            for the next six months. All of these funds could be paid in advance
            of the completion of this agreement. Any funds not so advanced will
            be paid at the point where ownership of the subsidiary transfers to
            CNC.

      f.    CTI agrees to reimburse CNC an amount equal to 35% of the annual
            salary of any CNC employee (acquired through the acquisition of the
            subside") that returns to CTI or its other subsidiaries within one
            year of said acquisition.

      g.    CTI agrees to use its best efforts to ensure that all employees of
            the subsidiary stay with the entity when the transfer to CNC occurs.

10)   Sections 4 and 7 shall be modified to require joint agreement by both CTI
      and CNC on all matters relating to the hiring and compensation of the
      employees employed by the subsidiary.

11)   In the event CNC determines that it requires additional local access POP
      locations, before CNC executes an agreement with any other person to
      provide such locations to CNC, CTI will negotiate for a period of thirty
      (30) days with CNC for CTI to provide such locations. In the event that
      CTI and CNC are unable to reach agreement within such 30 days, CNC shall
      thereafter be free to execute an agreement with any other person to
      provide such locations to CNC so long as the terms of such agreement when
      considered in the aggregate (including such matters as price, facilities,
      response times and other relevant factors bearing on the overall value of
      such an arrangement to CNC), are no more favorable to such other person
      that the most favorable terms offered by CNC in writing to CTI during such
      30 days of negotiation.

12)   CTI agrees to provide other consulting services to CNC at a rate not to
      exceed the lowest offered by CTI to other customers requiring similar
      services (including duration or quantity of such services).

- -------------------------

      [*] Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.
<PAGE>
 
13)   CNC and CTI agree to mutually recommend each other as business
      opportunities arise. Specifically, CNC will recommend CT1 services, as
      appropriate, to STET/TMI.

14)   Effective upon the closing of any Acquisition of CTI, CTI shall pay, or
      cause the person acquiring CTI to pay, to CNC the sum of [**] Such
      sum shall be paid in cash unless the consideration paid to CTI or the
      shareholders of CTI in the Acquisition consist solely or partly of
      securities of the acquirer which can be traded on the NASDAQ National
      Market, the New York Stock Exchange or the American Stock Exchange, in
      which case the acquirer shall have the right to pay such amount to CNC in
      a combination of cash and such securities in the same proportion and
      manner that such cash and securities is paid to CTI or the shareholders of
      CTI. Such securities shall be valued for the purposes of this agreement at
      the average of the closing sale price of such securities for the 30
      trading days preceding the closing of such Acquisition. In the event that
      the total consideration for the Acquisition is paid in two or more
      increments, the [*] to be paid to CNC shall be paid concurrently with
      each such increment. The proportion of the [*] paid at each Increment
      shall be the same proportion as the consideration paid at such increment
      represents as a portion of the total consideration paid in all increments.
      For purposes of this Agreement, an "Acquisition" shall mean any of
      transactions or series of transactions in which all or substantially all
      the business of CTI is transferred to another person, whether the form of
      such transaction is a stock sale by the shareholders of CTI, a merger, a
      consolidation or a transfer of assets.





- -------------------------

      [*]Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.
<PAGE>
 
If you agree with these changes, please note your acceptance below.  If I can
clarify any of the items notes, please contact me.

Accepted and Agreed:                           Accepted and Agreed:

Critical Technologies, Inc.                    Concentric Network Corporation
<TABLE> 
<S>                                            <C> 
By:    /s/ Matthew W. Bross                    By:    /s/ Michael Anthofer
   ----------------------------                   ----------------------------
       Matthew W. Bross                               Michael Anthofer
       Vice President & CEO                           Vice President & CFO

Date:  9-30-96                                 Date:  9-30-96
     --------------------------                     --------------------------
</TABLE> 
cc:    James A. Wootten
       Michael Fallon
       Paul W. Noblett
       John Peters

                                      -26-
<PAGE>
 
                    EMPLOYEE SERVICES AND STAFFING AGREEMENT

                                SECOND AMENDMENT


WHEREAS:  Concentric Network Corporation, a Florida corporation ("CNC"), and
Critical Technologies Incorporated, a Missouri corporation ("CTI"), are parties
to that certain Employee Services and Staffing Agreement (the "Staffing
Agreement dated as of November 1, 1995, and

WHEREAS:  CNC and CTI entered into an Extension and Amendment of the Staffing
Agreement on September 30, 1996 (the "Extension and Amendment"), which provides,
among other things, that the CNC Board of Directors must agree that all
"performance shares" or options to be granted under the Staffing Agreement have
been earned, and CNC must grant and deliver all option agreements under the
Staffing Agreement within 10 days of the first Board meeting following the
signing of the Extension and Amendment, which Board meeting was held on October
4,1996, and

WHEREAS:  The Extension and Agreement further provides that failure of the CNC
Board to approve said two items will nullify the Extension and Amendment, and

WHEREAS:  CTI and CNC agree that said option agreements should not be issued or
delivered until CNC has obtained from the State of Missouri appropriate waiver,
exemption, clearance or qualification for such options, the obtaining of which
will require more time than 10 days from October 4, 1996, and wish to amend the
Staffing Agreement, as amended, to enable CNC to obtain the appropriate Blue Sky
clearance without adverse effect on the Extension and Amendment,

NOW THEREFORE, CTI and CNC hereby agree as follows:

1.    The Extension and Amendment is hereby amended to provide that CNC will
promptly apply for the necessary Missouri waiver, exemption, clearance or
qualification for the options and the 900,000 shares of Class A Common Stock
issuable upon exercise of such options, and will promptly issue option
agreements with respect to such options within five business days of receipt of
such waiver, exemption, clearance or qualification from the State of Missouri;
provided that the vesting of such shares over the 12-month period provided in
the Staffing Agreement shall not be postponed on account of the Missouri
application but shall continue as provided for in the Staffing Agreement.

2.    As amended by the foregoing, the Staffing Agreement and the Extension and
Amendment shall remain in full force and effect and shall not be nullified on
account of delays related to obtaining Missouri Blue Sky approval; provided,
however, that if such options are not issued on or before December 21, 1996,
this Second Amendment to the Staffing Agreement shall terminate and the rights
of the parties shall be determined in accordance with the terms of the Employee
Servicing and Staffing Agreement and the First Amendment thereto, as if this
Second Amendment had not been executed.
<PAGE>
 
      IN WITNESS WHEREOF, the parties have executed this Second Amendment by
their duly authorized representatives as of the date set forth below.

<TABLE>
<CAPTION>
 
 
CONCENTRIC NETWORK                          CRITICAL TECHNOLOGIES
CORPORATION                                 INCORPORATED
<S>                                         <C>
 
By:       /s/ Mike Anthofer                 By:        /s/ Matthew W. Bross
   --------------------------------            -------------------------------

Name:     Mike Anthofer                     Name:      Matthew W. Bross
     ------------------------------              -----------------------------

Title:    Vice President & CFO              Title:     Vice President
      -----------------------------               ----------------------------

Date:     10-23-96                          Date:      10-21-96
     ------------------------------              -----------------------------
</TABLE>
<PAGE>
 
AMENDMENT No.  1 TO THE COLOCATION SERVICES AGREEMENT DATED NOVEMBER 1, 1994
BETWEEN CONCENTRIC RESEARCH CORPORATION AND CRITICAL TECHNOLOGIES, INC.

     This Amendment No.1 ("Amendment") dated as of June ___, 1997 by and between
Concentric Network Corporation ("CNC"), a Florida corporation with principal
offices at 10590 N. Tantau Avenue, Cupertino, California 95014 and Critical
Technologies Incorporated ("CTI"), a Delaware corporation with principal offices
at 944 Anglum, Hazelwood, Missouri 63042.

                                   WITNESSETH
                                   ----------

     WHEREAS, On November 1, 1994, CTI entered into the Colocation Services
Agreement (the "Agreement") with Concentric Research Corporation, now known as
Concentric Network Corporation;

     WHEREAS, the Agreement has been modified by the parties in the past and
needs to be modified to reflect the May 30, 1997 Memorandum of Understanding
("MOU") between CNC and Williams Communications Group, Inc.  ("WCG"), the parent
company of CTI;

     WHEREAS, the parties have agreed to incorporate all prior modifications and
the modifications contemplated in the MOU in this Amendment.

     NOW, THEREFORE, in consideration of the respective covenants and agreements
of the parties contained herein, the parties hereto agree as follows.

1.   Prior Modifications and Amendments
     ----------------------------------

     CTI and CNC agree that this Amendment shall supersede and replace any prior
amendments or modifications to the Agreement in their entirety.  Such prior
modifications and amendments shall be of no further force or effect.

2.   Amendments
     ----------

     2.1  The term of the Agreement shall be extended until December 31, 2000.
The Agreement may be terminated prior to December 31, 2000 by the mutual,
written consent of both parties.  The Agreement shall automatically renew for an
additional two-year period unless either party shall give one-hundred twenty
(120) days notice prior to the expiration of this Agreement to the other party
that said party does not wish to extend the terms of this Agreement.
Notwithstanding the foregoing, if WCG elects not to participate in the
"Financing Event", even though CNC has satisfied all conditions set forth in the
definition of "Financing Event", the Agreement may be terminated by CNC on
October 31, 1999, if CNC provides CTI ninety (90) days prior written notice.
The term "Financing Event" shall have the meaning set forth in the Amended and
Restated Employee Staffing and Services Agreement of even date herewith.
<PAGE>
 
     2.2  At the termination of the Agreement, CTI will assign its rights to the
POPs under the Agreement to CNC.  The assignment shall be subject to CTI's right
to colocate equipment.

     2.3  CNC may close any POP or, with the mutual agreement of CTI, migrate
any POP to a new location (i) not owned by WCG or its subsidiaries or (ii) not
managed by CTI during the term of the Agreement by paying to CTI the net present
value (at prime) of the remaining CTI profit on such POPs and by reimbursing CTI
for any out-of-pocket costs associated with leaving the former POP location
prior to the end of the term of the Agreement.  Notwithstanding the foregoing,
if CNC and CTI agree to migrate a CNC POP to a new location either (i) owned by
WCG or its subsidiaries or (ii) managed by CTI during the term of the Agreement,
then CNC shall only be required to reimburse CTI for any out-of-pocket costs
associated with leaving the former POP location prior to the end of the term of
the Agreement.  In this regard, CTI and CNC will work together to migrate a POP
or POPs, as identified by CNC, to new central office quality colocate space
under the Agreement as soon as commercially reasonable.  Further, CTI agrees
that the new central office quality colocate space shall be charged to CNC at
commercially competitive rates.

     2.4  CNC will pay the amounts set forth in the Agreement based upon a
minimum of one hundred (100) POP sites at all times during the term of the
Agreement.

     2.5  CTI will continue to be responsible for provisioning new POP sites for
CNC. CTI will be paid [*] for each installation. All direct costs of any new
POP shall be paid by CNC.

     2.6  CTI shall be allowed to colocate equipment in the CNC POPs controlled
by CNC based upon a percentage of floor space utilized.  Such cost to CTI to be
that percentage of the Colocate cost plus twenty percent [*] of the fees paid
by CNC to the party leasing the colocate space for square footage in the POP
locations.

     2.7  In the event that CNC determines that it requires additional local
access POP locations, before CNC executes an agreement with any other person to
provide such locations to CNC, CTI will negotiate for a period of thirty (30)
days with CNC for CTI to provide such locations.  In the event that CTI and CNC
are unable to reach agreement within such 30 day period, CNC shall thereafter be
free to execute an agreement with any other person to provide such locations to
CNC so long as the terms of such agreement, when considered in the aggregate
(including such matters as price, facilities, response times and other relevant
factors bearing on the overall value of such an arrangement to CNC), are no more
favorable to such other person than the most favorable terms offered by CNC in
writing to CTI during such 30 days of negotiation.

     2.8  New paragraphs c. and d. shall be added to Article XIV of the
Agreement.  These paragraphs shall read as follows:

     c.   Procedure:
          --------- 

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                      -2-
<PAGE>
 
     An Event of Default by either party shall not have occurred until the 
     non-defaulting party shall notify the defaulting party, in writing, of the
     default, setting forth the nature thereof. Said notice shall be mailed to
     the company at the designated address for notices as provided in Section 4
     of the Amendment. The defaulting party shall have thirty (30) days from the
     date of the notice to cure said defect or default.

     d.   Limitation of Liability:
          ----------------------- 

     Except as expressly and specifically set forth in another paragraph to this
     Agreement, neither party shall be liable to the other party for any lost
     profits; any loss of business; any cost of replacement services; or any
     indirect, consequential, incidental or special losses or damages of any
     kind or nature whatsoever, due to an Event of Default.


3.   Successors and Assigns
     ----------------------

     The Agreement, as amended, and all rights hereunder shall inure to the
benefit of and be enforceable by each party's successors and permitted assigns.
No party may assign or transfer this Agreement or transfer its rights or
obligations hereunder without the prior written consent of the other party
(which shall not be unreasonably withheld) except to an affiliate.

4.   Notices
     -------

     For the purposes of this Agreement and the Amendment, notices and all other
communications provided for in the Agreement and Amendment shall be in writing
and shall be deemed to have been duly given or delivered upon receipt after
personal delivery or mailing by registered mail, return receipt requested,
postage prepaid, address as follows:

     (a)  If to CTI:

          Critical Technologies Incorporated
          Attn: Gordon Martin
          111 East First Street
          Tulsa, OK 74103-2808
          Phone: 

          with a copy to:

          General Counsel
          Williams Telecommunications Group, Inc.
          One Williams Center
          Suite 4000
          Tulsa, OK 74172
          Phone:  
          Facsimile:  

                                      -3-
<PAGE>
 
                (b)  If to CNC:

          Concentric Network Corporation
          10590 N. Tantau Avenue
          Cupertino, CA 95014
          Attention:  Chief Financial Officer
          Phone:  (408) 342-2800
          Facsimile:  (408) 342-2810
    
          with a copy to:
    
          Wilson, Sonsini, Goodrich & Rosati
          650 Page Mill Road
          Palo Alto, CA 94304
          Attention: David Segre
          Facsimile:  

or to such other address as any party may have furnished to the other in writing
in accordance herewith.

5.   Amendment
     ---------

     No amendment or modification of this Agreement, as amended, or any of its
provisions shall be binding upon any party unless made in writing and signed by
all of the parties hereto.

6.   Waiver
     ------

     The performance of any condition or obligation imposed hereunder upon any
party hereto may be waived only upon the written consent of the parties hereto.
Such waiver shall be limited to the terms thereof and shall not constitute a
waiver of any condition or obligation of the other party under this Amendment.
Any failure by any party to this Amendment to enforce any provision shall not
constitute a waiver of that or any other provision of this Amendment.

7.   Third Party Rights
     ------------------

     This Amendment shall not inure to the benefit of any third party other than
CTI and CNC and valid successors or assigns of a party hereto or thereto.

                                      -4-
<PAGE>
 
     IN WITNESS WHEREOF, the parties have executed this Amendment by their duly
authorized representatives as of June 19, 1997.


CONCENTRIC NETWORK                            CRITICAL TECHNOLOGIES
CORPORATION                                   INCORPORATED

By: /s/                                       By: /s/
   -------------------------------               -------------------------------

Name:                                         Name:
     -----------------------------                 -----------------------------

Title:                                        Title:
      ----------------------------                  ----------------------------

                                      -5-

<PAGE>
                                                                      
                                                                   EXHIBIT 10.19
                                                                   -------------
     
                                    
                               AMENDMENT NO. 3 TO
                       INTERNET ACCESS SERVICES AGREEMENT      

         
     THIS AMENDMENT NO. 3 TO INTERNET ACCESS SERVICES AGREEMENT ("Amendment") is
made and effective as of August 23, 1996 (the "Effective Date"), by and between
Intuit Inc., a Delaware corporation ("Intuit"), and Concentric Network
Corporation, a Florida corporation ("Concentric or "CNC"), with reference to the
following facts:      

                                        
                                    RECITALS      
                                    --------

         
     A.   Intuit and CNC are parties to that certain Internet Access Services
Agreement effective as of August 1, 1995, as amended by that certain Amendment
No. 1 to Internet Access Services Agreement dated August 15, 1996, and that
certain Amendment No. 2 to Internet Access Services Agreement dated October 31,
1996, and as the meaning of certain of its provisions were confirmed pursuant to
that certain Acknowledgment and Limited Waiver dated August 20, 1996
(collectively, the "Access Agreement").      

         
     B.   The Access Agreement includes a license of the CNC Software, as
defined therein.      

         
     C.   CNC has entered into an ISP and Software OEM Agreement (the
"Quarterdeck Agreement") with Quarterdeck Corporation ("Quarterdeck") dated
August 23, 1996, by which CNC has access to Quarterdeck's stack and dialer
software, which is useful for Internet access in conjunction with the CNC
Software.      

         
     D.   The parties desire to add the Quarterdeck stack and dialer program to
the CNC Software sublicensed to Intuit pursuant to the Access Agreement.      

    
NOW, THEREFORE, for valuable consideration, the parties hereto desire to
memorialize their past agreements on the subject matter hereof and agree as
follows:      

         
     1.   Except as otherwise defined herein, capitalized terms shall have
the meaning given them in the Access Agreement.      

         
     2.   CNC hereby represents and warrants that it has all necessary rights
and licenses to grant to Intuit the sublicense for the use, reproduction and
distribution of the Quarterdeck Product as contemplated by this Amendment.      

         
     3.   The Access Agreement is hereby amended as follows:      

              
         a. Section 1.5 is hereby deleted and replaced in its entirety with the
following: ""CNC Code" shall mean the POP, login server, registration server,
Quarterdeck Product, encryption, data security and other software, including
object code and source code, described or referred to in this Agreement, and
developed by CNC or its suppliers to support the Internet Services provided by
Intuit, including any related documentation."      

              
          b. Section 7.3 is hereby amended to add the following provisions at
the end of such section: "CNC represents and warrants that the Quarterdeck
Agreement provides that Quarterdeck will indemnify CNC's sublicensees (such as
Intuit) with respect to losses, costs or expenses incurred by such sublicensee
(the "Quarterdeck Indemnity") as a result of a claim that the Quarterdeck
Product by itself infringes any patent, copyright or other intellectual property
right of      

                                       1
<PAGE>
 
     
any third party (as used herein, a "Quarterdeck Product Claim"). Therefore,
notwithstanding the foregoing indemnity obligation of CNC in favor of Intuit, so
long as Quarterdeck performs its obligations as provided in the Quarterdeck
Indemnity in favor of Intuit, CNC shall not be required to indemnify Intuit for
any Quarterdeck Product Claim."      

              
          c.  Exhibit F is hereby deleted in its entirety and replaced with the
Amended and Restated License Agreement in the form of Exhibit F attached hereto.
References in the Access Agreement to the "License Agreement" from and after the
Effective Date of this Amendment shall be understood to refer to the attached
Exhibit F. Concurrent with the execution and delivery of this Amendment, Intuit
and CNC shall execute and deliver to the other party the Amended and Restated
License Agreement attached hereto.      

         
     4.   Except as otherwise provided in this Amendment, the terms and
conditions of the Access Agreement remain in full force and effect.      

         
     IN WITNESS WHEREOF, the parties have executed and delivered this Amendment
as of the Effective Date and it shall be deemed accepted and made in San Diego,
California.      

    
INTUIT INC.                            CONCENTRIC NETWORK
                                       CORPORATION


By: /s/ WILLIAM HARRIS                 By: /s/ MICHAEL ANTHOFER
   ---------------------------            ---------------------------
   William Harris                         Michael Anthofer
   Executive Vice President               Senior President & Chief Financial
                                          Officer

   6220 Greenwich Drive                   10590 North Tantau Avenue
   San Diego, CA 92122                    Cupertino, CA 95014      

                                       2
<PAGE>
 
                                      
                                  EXHIBIT "F"

                     AMENDED AND RESTATED LICENSE AGREEMENT      

         
     THIS AMENDED AND RESTATED LICENSE AGREEMENT ("Agreement") is effective as
of August 23, 1996 (the "Effective Date"), by and between Intuit Inc., a
Delaware corporation ("Intuit"), and Concentric Network Corporation, a Florida
corporation formerly known as Concentric Research Corporation ("CNC"), with
reference to the following facts:      

                                        
                                    RECITALS      
                                    --------
         
     A.   CNC and Intuit have entered into that certain Internet Access Services
Agreement effective as of August 1, 1995, as amended by that certain Amendment
No. 1 to Internet Access Services Agreement dated August 15, 1996, and that
certain Amendment No. 2 to Internet Access Services Agreement dated October 31,
1996, and as the meaning of certain of its provisions were confirmed pursuant to
that certain Acknowledgment and Limited Waiver dated August 20, 1996
(collectively, the "Access Agreement") pursuant to which CNC agreed to license
the use of the CNC Code to Intuit.      

         
     B.   CNC has entered into an ISP and Software OEM Agreement (the
"Quarterdeck Agreement") with Quarterdeck Corporation ("Quarterdeck") dated
August 23, 1996, by which CNC has access to Quarterdeck's stack and dialer
software, which is useful for Internet access in conjunction with the CNC
Software.      
 
         
     C.   The parties desire to add the Quarterdeck stack and dialer program
to the CNC Software sublicensed to Intuit pursuant to the Agreement.      

         
     NOW, THEREFORE, for valuable consideration, receipt of which is hereby
acknowledged, the parties hereto agree as follows:      

     
1.   Definitions.      
     ----------- 

         
     1.1  "CNC Code" shall mean the POP, login server, registration server,
Quarterdeck Product, encryption, data security and other software described in
or relating to the performance of the Access Agreement, including any related
documentation, and developed by CNC or its suppliers during the Term of the
Access Agreement to support the Internet Services provided by Intuit, including
any related documentation.      
 
         
     1.2  "Quarterdeck Product" is Quarterdeck software, in object code form,
as further described in Attachment 1 attached hereto.      
 
         
     1.3  Any other capitalized terms not defined herein shall have the meaning
given them in the Access Agreement.      

    
2.   Grant of License.      
     ---------------- 

         
     2.1  Subject to Sections 2.4 and 2.5 below, CNC hereby grants to Intuit
(or its designee, e.g., a replacement Internet access service provider) a world-
wide, non-exclusive, fully paid, perpetual right and license (i) to use all or
any portion of the CNC Code in connection with the production, copying, license,
distribution and sale of the Products, including any portion of the CNC      

                                       3
<PAGE>
 
    
Code which may be distributed or made available to the Customers in order for
them to properly access the CNC Network, and (ii) to sublicense the copying and
use of the CNC Code to the Customers in connection with the Customers' use of
the Products, provided that Intuit's right to distribute the CNC Code to its
Customers shall extend only during the Term and Transition Period. However,
nothing in this Agreement (except, with respect to the Quarterdeck Product, as
otherwise set forth in Sections 2.4 or 2.5 herein) or the Access Agreement shall
affect the continuing right (i) of Intuit to distribute Product containing the
CNC Code that may be in the process of manufacture or held in inventory at the
time that the Term of the Access Agreement terminates or expires, or (ii) of the
Customers to use the CNC Code that is contained in any Product that they may
acquire.      

         
     2.2  The grant to Intuit in Section 2.1 includes the right to use, modify,
adapt, copy, display and otherwise exploit the CNC Code in any manner reasonably
necessary or advisable for Intuit (or its designee) to provide Internet services
or access to the Customers during or after the Term of the Access Agreement. 
     

          
      2.3  CNC and Intuit intend that the license granted to Intuit pursuant
to this Agreement shall ensure (A) that Intuit is able (i) to smoothly, quickly,
cost-effectively and efficiently transition the CNC Services from CNC to another
access services provider and (ii) to provide high quality services at the
performance levels specified in the Access Agreement to the Customers on a
continuous basis in the event of such a transition, and (B) that the Customers
are able to use the Internet Services during, from and after such a transition.
However, the definition of the CNC Code and the scope and the duration of the
license and rights granted in this Agreement are not intended to extend beyond
the definition, scope and duration, as applicable, that Intuit reasonably
determines in good faith to be necessary or advisable to accomplish the
intention of the parties as expressed in the foregoing sentence or in the Access
Agreement.      
 
         
     2.4  Notwithstanding anything to the contrary in this Agreement (including
the last sentence of Section 2.1) or in the Access Agreement, Intuit's license
with respect to the Quarterdeck Product shall be governed by the restrictions
set forth in this Section 2.4 and the following Section 2.5. Intuit shall have
no right to modify, adapt or otherwise exploit the Quarterdeck Product except to
incorporate the Quarterdeck Product into or bundle the Quarterdeck Product with
the Products and to reproduce, market and distribute the resulting bundled
product ("Bundled Product") and associated end user documentation, provided that
the following provisions are adhered to:      

              
          a. Bundling Requirements. The software application with which the
             ---------------------                                         
Quarterdeck Product is bundled or incorporated must offer substantial
functionality over and above that of the Quarterdeck Product, and Intuit must
market and promote the Bundled Product in a manner that primarily emphasizes the
functionality and features of the Product rather than those of the Quarterdeck
Product. The Bundled Product must be configured in such a manner that the
Quarterdeck Product can only be used by Intuit's end user customers to permit
them to utilize CNC as an Internet Service Provider to access the Internet or
world wide web generally, or in such other manner of configuration as
Quarterdeck may approve in writing from time to time in accordance with the
Quarterdeck Agreement.      

              
          b. End-User License and Proprietary Rights. Copies of the Quarterdeck
             ---------------------------------------                           
Product distributed by Intuit as part of a Bundled Product must contain such
proprietary rights notices in the name of Quarterdeck as Quarterdeck reasonably
designates, and copies of the Quarterdeck Product distributed by Intuit as part
of a Bundled Product must be accompanied by and licensed pursuant to Attachment
2 hereto such that the terms and conditions of Attachment 2 are displayed      

                                       4
<PAGE>
 
     
to the user and the user must affirmatively manifest its consent and agreement
to such terms by clicking on an "accept" button on the display before the
installation and configuration of the Quarterdeck Product is completed and the
Quarterdeck Product is rendered fully usable.      

              
          c. Royalties for Software OEM Distributed Copies.      
             --------------------------------------------- 

                 
             (1) Intuit shall pay to CNC royalties in an amount of [*] for
each copy of the Quarterdeck Product sublicensed by Intuit to an end User
customer who remains a registered user of CNC as an Internet Service Provider
for a period of greater than thirty (30) days subsequent to the effective date
of such customer subscribing for Full Internet Services.      

                 
             (2) Advance. Intuit will pay to CNC on or before the Effective Date
                 -------
of this Agreement the sum of [*] (the "Advance"), which shall constitute an
advance fully creditable against license fees for the Quarterdeck Product
otherwise payable to CNC by Intuit pursuant to Section 2.4(c)(1). By way of
example, if Intuit issued a total of 15,000 sublicenses during the first three
calendar quarters pursuant to Section 2.4(d) below, then the effective amount
of the Advance against which credits would be applied for future quarters
would be reduced to [*].      

              
          d. Timing And Reports. For each calendar quarter during the period
             ------------------
wherein CNC is permitted to distribute the Quarterdeck Product and subsequent to
January 31, 1997, and commencing with respect to the first such calendar
quarter, Intuit shall submit to CNC, within fifteen (15) days following the end
of each quarter a royalty report which shall specify the number of units of the
Quarterdeck Product sublicensed by Intuit during the previous quarter based on
the number of subscribers for Full Internet Access; provided, that CNC will
cooperate with Intuit and provide any information that Intuit may require in
order to submit such report. CNC shall have the right to charge interest on any
payment which is more than ninety (90) days past due, at a rate equal to the
lesser of (i) one and one half percent (1 1/2%) per month; or (ii) the maximum
rate allowed by law.      

              
          e. Audit Rights. Intuit shall allow Quarterdeck's representatives
             ------------ 
and/or independent auditors to audit and analyze appropriate and relevant
accounting records of Intuit's premises solely to verify accurate and full
accounting for and payment of all moneys due Quarterdeck under this Agreement
and Intuit's other compliance with the terms of this Agreement. Any discrepancy
in the amount of royalties due shall be corrected promptly by Intuit, in the
case of an underpayment, or by Quarterdeck, in the case of an overpayment, and
if any such audit discloses a discrepancy of more than ten percent (10%) of the
amount due from Intuit for the period as to which the discrepancy has arisen,
Intuit shall pay the cost of the audit. Any such audit shall be during Intuit's
normal business hours, upon ten (10) business days written notice by
Quarterdeck. No audit (other than the first audit) may be conducted less than
twelve (12) months after the previous audit.      

              
          f. Termination of Quarterdeck Agreement.      
             ------------------------------------ 

                 
             (1) Intuit's rights under Section 2.1 of this Agreement with
respect to the Quarterdeck Product shall cease upon termination of the
Quarterdeck Agreement except that Intuit may sell any copies of the Quarterdeck
Product in its inventory for a period of ninety (90) days after such
termination; provided, however, that CNC shall notify Intuit if CNC's rights
under the Quarterdeck Agreement's related sell-off provisions are extended or
improved in any way and, in such case, such extended or improved rights shall
automatically be deemed to be granted to Intuit      

     
[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.      


                                       5
<PAGE>
 
     
pursuant to this section (although the parties shall execute an amendment to
this Agreement at either party's request to memorialize such new or revised
terms).      

               
          (2) During the Term of the Access Agreement and so long as Intuit is
using the Quarterdeck Product, CNC hereby covenants that:      

                  
              (a) CNC shall fully perform its obligations under the Quarterdeck
Agreement; provided, however, that if CNC fails to perform any of its material
obligations under the Quarterdeck Agreement or is notified by Quarterdeck to
that effect, then CNC shall give Intuit immediate written notice of such
occurrence and use its best efforts to remedy such failure so that the
Quarterdeck Agreement shall not be terminated;      

                  
              (b) CNC shall not without Intuit's written consent take action to
terminate the Quarterdeck Agreement with or without cause; and      

                  
              (c) CNC shall give Intuit written notice within three days if
Quarterdeck notifies CNC of Quarterdeck's intention to terminate the Quarterdeck
Agreement.      

         
     g. Taxes. Intuit shall be solely responsible for any federal, state,
        -----                                                            
provincial or local sales, use, value added or other tax, tariff, duty or
assessment customarily levied or imposed on a sublicensor arising out of or
related to the payment of royalties by Intuit to CNC under this Section 2.4,
other than any tax based on the revenues or income of Quarterdeck or CNC. Intuit
shall pay directly, or reimburse Quarterdeck or CNC for, the amount of such
sales, use, value added or other tax, tariff, duty or assessment which
Quarterdeck or CNC are at any time obligated to pay or collect.      

         
     h. Reverse Engineering. Intuit may not modify any Quarterdeck Product, any
        -------------------                                                    
copies of any of the Quarterdeck Products or any documentation associated with
any of the Quarterdeck Products, except as expressly and clearly permitted by
this Agreement. Intuit shall not disassemble, decompile or otherwise reverse
engineer all or any part of any of the Quarterdeck Products or assist any third
party to do any of the foregoing.      

         
     i. U.S. Export Control. Intuit understands and acknowledges that the
        -------------------                                              
Quarterdeck Product is subject to regulation by agencies of the U.S. Government,
including, but not limited to, the U.S. Department of Commerce, which prohibit
export or diversion of certain products and technology to certain countries.
Intuit warrants that it will comply with the Export Administration Regulations
and other United States laws and regulations governing exports in effect from
time to time."      

         
     2.5  In addition to its rights granted pursuant to Section 2.4 relating to
the Quarterdeck Product, CNC hereby grants to Intuit a limited non-exclusive
license before the termination of the Quarterdeck Agreement to use the
Quarterdeck Materials (as defined in the Quarterdeck Agreement) and to
manufacture and use internally, solely for purposes of marketing, promotion,
demonstration and technical support to end users, a number of copies of the
Quarterdeck Product equal to one (1) for each Intuit employee and a reasonable
number of copies solely for back-up or archival purposes. Intuit shall reproduce
on all copies of the Quarterdeck Product reproduced by Intuit pursuant to this
Section 2.5 such proprietary rights notices in the name of Quarterdeck as
Quarterdeck reasonably designates. All such copies used by Intuit shall be
governed by and subject to the terms of the standard Quarterdeck License And
Limited Warranty supplied with the Quarterdeck Product, a copy of which is
attached as Attachment 2 to this Agreement.      

                                       6
<PAGE>
 
     
3.   No Infringement. CNC represents and warrants on a continuing basis that
     ---------------                                                        
neither the CNC Code, nor the exercise by Intuit of any of the rights granted
under this Agreement, will infringe any intellectual property right of any third
party and that there is no litigation or claim pending or, to CNC's knowledge,
threatened relating thereto. CNC shall and hereby does indemnify and defend
Intuit and hold it harmless from and against any and all claims, liabilities,
losses, costs and expenses including, but not limited to, reasonable attorneys'
fees and costs of suit, incurred by Intuit as a result of or arising from any
claim or proceeding made or brought against Intuit that the use, reproduction,
marketing, sale, sublicensing or distribution of CNC Code infringes any patent,
copyright or other rights of any third party, or that the CNC Code is defective.
This indemnity shall not apply to the extent such claims result from Intuit's
own modification or alteration of the CNC Code. Intuit shall promptly notify CNC
of any such claim(s) of which it becomes aware and shall, at CNC's request and
expense, cooperate in the investigation and defense of such claim(s).      

    
4.   Miscellaneous.      
     ------------- 

         
     4.1  Entire Agreement. This Agreement shall be governed by and construed in
          ----------------
accordance with the substantive laws of the State of California (not including
its choice of law provisions). This Agreement, as supplemented by the Access
Agreement, constitutes the entire understanding between the parties with respect
to the licensing of the CNC Code contemplated herein. This Agreement shall not
be modified except in a writing signed by and exchanged between both of the
parties and expressly referencing this Agreement. A waiver of any provision of
the Agreement or any right or obligations of either party hereunder shall be
effective only if made pursuant to a writing signed and delivered by the party
waiving compliance. Except as provided therein, any such written waiver shall
not be construed as, or constitute, a continuing waiver of such breach, or of
other breaches of the same or other provisions of this Agreement. Neither party
shall by mere lapse of time without giving notice or taking other action
hereunder be deemed to have waived any breach by the other party of any of the
provisions of this Agreement. This Agreement shall be binding on all successors
and assigns of the parties.      

         
     4.2  No Executory Obligation. CNC acknowledges that this Agreement is not
          ----------------------- 
an "executory contract" within the meaning of the U.S. Bankruptcy Code and shall
not be subject to rejection by any debtor-in-possession, bankruptcy trustee or
the like.      

         
     4.3   Severability. If any provisions of this Agreement shall be held by a
           ------------                                                        
court, arbitrator or other tribunal of competent jurisdiction to be invalid or
unenforceable, such provisions shall be      

                                       7
<PAGE>
 
     
deemed valid and enforced to the maximum extent permissible and the remaining
portions of this Agreement shall remain in full force and effect.      

         
     IN WITNESS WHEREOF, this Agreement shall be effective as of the Effective
Date and it shall be deemed accepted and made in San Diego, California.      

   
<TABLE> 
<S>                                    <C> 
INTUIT INC.                            CONCENTRIC NETWORK
                                       CORPORATION


By:                                    By:
   --------------------------             --------------------------
   William Harris                         Michael Anthofer
   Executive Vice President               Senior President & Chief Financial
                                          Officer

   6220 Greenwich Drive                   10590 N. Tantau Avenue
   San Diego, CA 92122                    Cupertino, CA 95014
</TABLE>      
                                       8
<PAGE>
 
                                 
                            EXHIBIT F - ATTACHMENT 1      
                            ------------------------

                           
                       DESCRIPTION OF QUARTERDECK PRODUCT      

    
The Quarterdeck Product consists of Quarterdeck's current version as of the date
of this Agreement of:      

    
MPKERNEL.EXE -- The Winsock dialer and protocol stack that Quarterdeck uses to
dial out via a modem and standard telephone line to obtain a PPP connection. 
     

    
The following ".dll" files that are required to enable to Winsock dialer to
work: MPLANG.DLL, INIFILES.DLL, MPCOMM.DLL, MPIAP.DLL, MPSCRIPT.DLL, MPSLIP.DLL,
MPTCPIP.DLL, WINSOCK.DLL.      

    
With the following changes:      

             
         (a) Menu selection in mpkernel.exe and icon for 'location manager',
'help', 'ping' to be removed.      
 
             
         (b) The "About Winsock" licensing information and serial number to be
changed."      

                                       9
<PAGE>
 
                                
                            EXHIBIT F - ATTACHMENT 2      
                            ------------------------

                                    
                                END USER LICENSE      

    
This License is your proof of license. Please treat it as valuable property. 
     

                         
                     QUARTERDECK END USER LICENSE AGREEMENT
                                 ("AGREEMENT")      

    
NOTICE TO END USER: CAREFULLY READ THIS AGREEMENT. USE OF THE SOFTWARE
("SOFTWARE") AND FONTS, IF ANY, PROVIDED WITH THIS AGREEMENT CONSTITUTES YOUR
ACCEPTANCE OF THE TERMS OF THIS AGREEMENT. IF YOU DO NOT AGREE TO THE TERMS OF
THIS AGREEMENT, PROMPTLY RETURN THE SOFTWARE AND THE ACCOMPANYING ITEMS
(INCLUDING WRITTEN MATERIALS, BINDERS AND CONTAINERS) TO THE LOCATION WHERE YOU
OBTAINED THEM FOR A FULL REFUND.      

    
1.   License Grant. Quarterdeck Corporation, ("QUARTERDECK"), hereby grants to
     -------------                                                            
you (either as an individual or entity) a nonexclusive sublicense subject to the
provisions of this AGREEMENT, to use the SOFTWARE solely for your own internal
personal or business purposes on a single computer (whether a standard computer
or a workstation component of a multi-user network). You may not copy the
written materials accompanying the SOFTWARE. This AGREEMENT is effective until
the year 2040.      

    
2.   Proprietary Rights. You acknowledge that the SOFTWARE is proprietary to
     ------------------                                                     
QUARTERDECK and its suppliers. You agree to hold the SOFTWARE in confidence,
disclosing the SOFTWARE only to authorized employees having a need to use the
SOFTWARE as permitted by this AGREEMENT and to take all reasonable precautions
to prevent disclosure to other parties.      

    
3.   Other Copies. You will not make, have made or permit to be made any copies
     ------------                                                              
of the SOFTWARE or portions of the SOFTWARE, except as necessary for its use
with a single licensed computer system under the terms and conditions of this
AGREEMENT. You agree that any such copies shall contain the same proprietary
notices which appear on or in the SOFTWARE.      

    
4.   Ownership. Except as stated above, this AGREEMENT does not grant you any
     ---------                                                               
rights to patents, copyrights, trade secrets, trade names, trademarks (whether
registered or unregistered), or any other rights, franchises or licenses in
respect of the SOFTWARE. Title to and ownership of the SOFTWARE, any
reproductions and any documentation of the SOFTWARE, shall remain with
QUARTERDECK and its suppliers. You will not adapt or use any trademark or trade
name which is likely to be similar to or confusing with that of QUARTERDECK or
any of its suppliers or take any other action which impairs or reduces the
trademarks rights of QUARTERDECK or its suppliers.      

    
5.   Other Restrictions. This AGREEMENT is your proof of license to use the
     ------------------                                                    
SOFTWARE in accordance with the terms of this AGREEMENT, and must be retained by
you. You may not rent or lease the SOFTWARE, but you may permanently assign your
rights under this AGREEMENT to an assignee of all of your right, title and
interest in and to the SOFTWARE, provided you transfer this AGREEMENT, all
copies of the SOFTWARE and all accompanying written materials, and such assignee
agrees to be bound by all the terms and conditions of this AGREEMENT. YOU MAY
NOT ALTER, MODIFY, REVERSE, ENGINEER, DECRYPT, DECOMPILE OR DISASSEMBLE THE
SOFTWARE.      

                                      10
<PAGE>
 
     
6.   Content. Title, ownership rights and intellectual property rights in and
     -------                                                                 
to the content accessed through the SOFTWARE is the property of the applicable
content owner and may be protected by applicable copyright or other law. This
License grants you no rights to such content.      

    
7.   Limited Warranty. QUARTERDECK warrants that the SOFTWARE will perform
     ----------------                                                     
substantially in accordance with the accompanying written materials and that the
printed materials and diskettes are free from any physical defects for a period
of ninety (90) days from the date of purchase. Any implied warranties on the
SOFTWARE, printed materials or diskettes are limited to ninety (90) days.      

    
8.   Customer Remedies. QUARTERDECK's entire liability and your sole and
     -----------------                                                  
exclusive remedy shall be, at QUARTERDECK's option, either to: (a) correct the
error; (b) help you work around or avoid the error; or (c) authorize a refund,
so long as the SOFTWARE, printed materials or diskettes are returned to
QUARTERDECK with a copy of your receipt. This Limited Warranty is void if
failure of the SOFTWARE has resulted from accident, abuse or misapplication. Any
replacement SOFTWARE will be warranted for the remainder of the original
warranty period.      

    
9.   No Other Warranties. QUARTERDECK DOES NOT WARRANT THAT THE SOFTWARE IS
     -------------------                                                   
ERROR FREE, AND QUARTERDECK DISCLAIMS ALL OTHER WARRANTIES, EITHER EXPRESS OR
IMPLIED, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS WITH
RESPECT TO THE SOFTWARE, THE ACCOMPANYING WRITTEN MATERIALS OR DISKETTES. SOME
JURISDICTIONS DO NOT ALLOW THE EXCLUSION OF IMPLIED WARRANTIES OR LIMITATIONS ON
HOW LONG AN IMPLIED WARRANTY MAY LAST, OR THE EXCLUSION OR LIMITATION OF
INCIDENTAL OR CONSEQUENTIAL DAMAGES, SO THE ABOVE LIMITATIONS OR EXCLUSIONS MAY
NOT APPLY TO YOU. THIS WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS AND YOU MAY ALSO
HAVE OTHER RIGHTS WHICH VARY FROM JURISDICTION TO JURISDICTION.      

    
10.  Export. You acknowledge that the laws and regulations of the United States
     ------                                                             
restrict the export and re-export of commodities and technical data of United
States origin, including the SOFTWARE. You agree that you will not export or re-
export the SOFTWARE in any form without the appropriate United States and
foreign government licenses. You agree that your obligations pursuant to this
Section of this AGREEMENT shall survive and continue after any termination or
expiration of rights under this AGREEMENT.      

    
11.  Severability. In the event of invalidity of any provision of this 
     ------------                                                     
AGREEMENT, such invalidity shall not affect the validity of the remaining
portions of this AGREEMENT. The United Nations Convention on Contracts for the
International Sale of Goods is specifically disclaimed.      

    
12.  No Liability For Consequential Damages. IN NO EVENT SHALL QUARTERDECK BE
     --------------------------------------                                  
LIABLE TO YOU FOR ANY CONSEQUENTIAL, SPECIAL, INCIDENTAL OR INDIRECT DAMAGES OF
ANY KIND ARISING OUT OF THE USE OF THE SOFTWARE, EVEN IF QUARTERDECK HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, AND IN NO EVENT WILL QUARTERDECK'S
LIABILITY FOR ANY CLAIM, WHETHER IN CONTRACT, TORT OR ANY OTHER THEORY OF
LIABILITY, EXCEED THE LICENSE FEE FOR THE SOFTWARE PAID BY YOU.      

    
13.  U.S. Government Restricted Rights. If this product is acquired under the
     ---------------------------------                                       
terms of a: (a) DoD contract, use, duplication or disclosure by the Government
is subject to restrictions as set forth in subparagraph (c)(1)(ii) of 252.227-
7013; or (b) agency contract, use, reproduction or disclosure is      

                                      11
<PAGE>
 
     
subject to 52.227-19 (a) through (d) and restrictions set forth in the
accompanying end user agreement. Unpublished-rights reserved under the
copyright laws of the United States. Quarterdeck Corporation, 150 Pico
Boulevard, Santa Monica, California 90405-1018.      

    
14.  Governing Law. This AGREEMENT is governed by the laws of the United States
     -------------                                                      
of America and the State of California.      

    
15.  Entire Agreement. This is the entire agreement between you and QUARTERDECK
     ----------------                                              
which supersedes any prior agreement, whether written or oral, relating to the
subject matter of this AGREEMENT.     

    
Should you have any questions concerning this AGREEMENT, or if you desire to
contact QUARTERDECK for any reason, please write: Quarterdeck Corporation, 150
Pico Boulevard, Santa Monica, California 90405-1018."      

                                      12

<PAGE>
 
                                                                   EXHIBIT 10.22

                                 MASTER LEASE

                            AGREEMENT NUMBER CON 01C

     This Agreement ("Agreement") is entered into this 4th day of August, 1994
by and between Racal-Datacom, Inc., a Delaware corporation, (hereinafter
referred to as "Lessor"), having its principal place of business located at 1601
North Harrison Parkway, Sunrise, Florida 33323-2899 and Concentric Research
Corporation, a Florida corporation (hereinafter referred to as "Lessee") having
its principal place of business at 400 Forty-First Street, Bay City, MI 48708.


                                WITNESSETH THAT

     WHEREAS, Lessor is the manufacturer of data communication products which
are composed of hardware (hereinafter referred to as "Equipment") and software
which is defined as a set of processor instructions that can be ported into a
processor and executed to provide a defined functionality (hereinafter referred
to as "Software"); and

     WHEREAS, Lessee is desirous of leasing such Equipment or Software from
Lessor for use with Lessee's communications network; and

     WHEREAS, both parties are desirous of establishing the terms and conditions
which shall govern all orders issued pursuant to this Agreement.

     NOW THEREFORE, in consideration of the covenants, premises and mutual
agreements contained herein, the parties do hereby agree as follows:

                                    PURPOSE
                                    -------

     The purpose of this Agreement is to set forth the terms and conditions
pursuant to which Lessee may submit orders (as defined in Article III) to
Lessor, All Orders must be accepted by Lessor at its headquarters, Sunrise,
Florida.
<PAGE>
 
II.  Term of Agreement
     -----------------

     This Agreement shall commence upon the date first written above and shall
continue for a term of twelve (12) months.  The Agreement shall govern all
Orders placed hereunder provided such orders are received by Lessor within
twelve (12) months and the Equipment and Software ordered is installed within
fourteen (14) months, both of said periods beginning upon the date of
commencement of this Agreement.  Thereafter, this Agreement shall automatically
renew itself in twelve (12) month increments unless either party notifies the
other of its decision to terminate this Agreement by providing the other party
sixty (60) days written notice prior to the expiration of the period then in
effect.

     Notwithstanding that this Agreement may terminate prior to the expiration
of an individual Orders term, it is expressly agreed that any Order issued
pursuant to this Agreement shall continue to be in full force and effect until
the expiration of such Orders stated minimum term, and shall continue to be
governed by the terms of this Agreement.

III. Ordering Procedure
     ------------------

     Lessee shall issue Orders to Lessor on Lessors order form or Lessee's order
form.  At a minimum, such Orders shall include the following information:

     a.  Description of Equipment to be leased and Software to be licensed.
     b.  Quantity of each item of Equipment or Software.
     c.  Monthly lease rate, license fee and lease term for each item.
     d.  Unit installation price for each item (if applicable).
     e.  Unit purchase price for each item.
     f.  Requested delivery date.
     g.  Shipping location and Lessee prime contact at shipping location.
     h.  Billing address and billing contact.
     i.  Required Lessor services such as standard handling, installation,
maintenance, training and engineering costs (if applicable), and their
respective charges.

     Lessor will acknowledge acceptance or rejection of orders within fifteen
(15) days after receipt of the order at Lessor's principal place of business,
Sunrise, Florida.  Once accepted, the order is noncancelable.  If Lessor
proposes a delivery schedule different from the schedule requested by Lessee,
Lessee must notify Lessor of its rejection of such alternate delivery schedule
within fifteen (15) days after mailing of such notification by Lessor, or the
Lessor acknowledged shipping date shall be deemed to be accepted by Lessee.

IV.  Commencement and Term of Order
     ------------------------------

     An Order for an individual unit of Equipment or Software shall be binding
from the date it is accepted by Lessor.  Commencement of term and monthly rental
as to each unit of Equipment and Software shall commence fifteen (15) days after
the deployment of CRC's Wide Area Network, the

                                      -2-
<PAGE>
 
Lessee, an AT&T , whichever first occurs (the "Commencement Date").  Monthly
rental for a diagnostic controller applicable, shall commence thirty (30) days
following the Deployment Date by Lessor.  The lease term shall continue for the
number of full months set forth on the Order, commencing on the first day of the
month following the Commencement Date.

     Network deployment shall mean that Lessors Equipment which is deployed at
the available sites set forth on the deployment schedule agreed to by the
parties and attached hereto as Exhibit 4 is operational.  Operational shall mean
that the Lessor supplied Equipment is functioning in accordance with the
parameters set forth in Exhibit 3 notwithstanding the operational capability or
lack thereof of any other equipment or services provided by any other party
relating thereto or in connection therewith.

     Lessee agrees to complete a Certificate of Acceptance for each unit of
Equipment and Software shipped under this Agreement.  Such Certificate of
Acceptance shall be forwarded to Lessor within seven days of the Commencement
Date set forth above and shall indicate that: (i) Lessee has fully inspected the
Equipment and Software; (ii) Lessee has acknowledged that the Equipment and
Software is in good condition and repair; and, (iii) Lessee agrees that the
Equipment and Software meets their respective Lessor published specifications.
Failure of Lessee to provide a Certificate of Acceptance shall not affect any
Lessee obligations set forth in this Agreement, including but not limited
to payment.

     The Order may be renewed for an extended term in accordance with Lessor's
policies in effect at time of the Order's expiration.  Either party must notify
the other in writing at least sixty (60) days prior to expiration of the lease
term of its decision to either renew the Order or terminate any or all of the
Equipment and Software leased thereunder.  Without such notice, the Order shall
continue at the same rate and under the same conditions until such sixty (60)
day notice is given by either party.

     Notwithstanding that the lease contemplates the lease term set forth on the
face of the Order, it is agreed that if Lessee is a governmental entity and is
fiscally funded, continuance of the Order for said term is dependent upon the
annual legislative approval of funding.  Lessee agrees to utilize its best
efforts to assure funding for the continuance of the Order; however, if fiscal
funding is denied, the Lessee may terminate the lease by providing Lessor with
written notice as outlined in this provision.

V.   Return of Equipment and Software
     --------------------------------

     Upon termination by expiration or otherwise of each Order, Lessee shall, at
Lessee's expense, disconnect the Equipment or de-install the Software and allow
Lessor to enter Lessee's premises to pack and ship the Equipment and Software.
Such Equipment and Software returned to Lessor shall be in the same condition as
delivered by Lessor, reasonable wear and tear excepted and capable of meeting
all recertification requirements.  If Lessor is not allowed to remove the
Equipment and Software as noted within two (2) weeks after the effective date of
Lessee's notice of termination, such termination shall be void, and the lease
shall continue in full force and effect until new notice is given followed by
removal of Equipment and Software in accordance with this paragraph.

                                      -3-
<PAGE>
 
VI.  Payment
     -------

     The Equipment and Software is to be leased for the term set forth on the
Order and is non-cancelable.  Lessee shall pay to Lessor, the monthly rate set
forth on the Order during each month of the term of such Order.  Lessors initial
                                                                 ---------------
payment due hereunder shall be paid on the fifteenth (15th) day following the
- -----------------------------------------------------------------------------
Commencement Date.  The remainder of the rental payments for the lease term
- ---------------------------------------------------------------------------
shall be due and payable on the first day of each calendar month thereafter.
- ---------------------------------------------------------------------------  
The Equipment furnished hereunder may be new, remanufactured or contain used
components at Lessor's option.  If the Commencement Date of each unit of
Equipment leased hereunder is other than the first day of each month, the first
payment due hereunder shall be equal to one thirtieth of the monthly rate set
forth on the Order for each day from and including the Commencement Date through
and including the last day of the month prior to the beginning of the term and
the monthly rate for the full initial month. Lessor reserves the right to impose
a late payment charge of one and one-half percent (1-1/2%) per month, but not in
excess of the lawful maximum, on any past due balance in the event Lessee shall
fail to pay any charges within fifteen (15) days after same are due, and Lessee
agrees to pay same.  If such rate exceeds the amount authorized by law in the
jurisdiction in which the Equipment or Software is located, interest shall be
computed at the maximum legal rate at that location.  Payments shall be made to
the Lessor address stated on each invoice.  Charges for Lessor services (such as
standard handling, installation, engineering costs (if applicable) and training)
shall also be at the prevailing rates at time of order.  Any applicable taxes
will be invoiced.

VII. Assignment
     ----------

     Without Lessor's prior written consent, Lessee shall not (a) assign,
transfer, pledge, hypothecate, or otherwise dispose of all or any part of
Lessee's right, title or interest in and to this Agreement, any Order, the
Equipment or Software, or (b) sublet or lend the Equipment or Software or permit
it to be used by anyone other than Lessee or Lessee's employees.  Lessor may
sell or assign or grant a security interest or participation in all or any part
of Lessor's right, title or interest in and to this Agreement, any Order and the
Equipment or Software without notice to Lessee, and Lessor's assignee or secured
party may then re-assign such interest without notice to Lessee.  Lessee agrees
that any such assignment or re-assignment shall not change Lessee's or Lessors
                                                                    ----------
duties or obligations under this Agreement or any Order and Lessee hereby
consents to any such assignment or re-assignment.  Each such assignee and/or
secured party shall have all the rights but none of the obligations of Lessor
under such Order unless Lessee is otherwise notified by Lessor.  Lessee shall
recognize such assignments and/or security agreements and agrees that upon
notice of such assignment it shall pay directly to assignee (unless otherwise
directed by assignee) without abatement, deduction or setoff all amounts which
become due hereunder and further agrees that it will not assert against assignee
any defense, counterclaim or setoff for any reason whatsoever in any action for
lease payments or possession brought by assignee.  Upon such assignment and
except as may otherwise be provided therein, all references in this Agreement to
Lessor shall include Assignee.

                                      -4-
<PAGE>
 
VIII. Net Lease
      ---------

     Lessee and Lessor acknowledge and agree that each Order constitutes a net
lease with all costs, expenses and liability associated with the Equipment or
Software or its Order to be borne by Lessee unless expressly agreed to the
contrary in writing by Lessor.  Subject to Lessee's right to terminate
hereunder, in the event an assignment of this lease by the Lessor, the Lessee's
obligations to pay all monthly rates and any and all amounts payable by Lessee
under any Order shall be to the assignee, absolute and unconditional and shall
not be subject to any abatement, reduction, set-off, defense, counterclaim,
interruption, deferment or recoupment for any reason whatsoever and that such
payments shall by and continue to be payable in all events.

IX.  Representations and Warranties of Lessee
     ----------------------------------------

     Lessee hereby represents, warrants and covenants that, with respect to this
Agreement and each Order executed hereunder

     a.  The execution, delivery and performance thereof by the Lessee have been
duly authorized by all necessary corporate action.

     b.  The individual executing such was duly authorized to do so.

     c.  This Agreement and each Order constitute legal, valid and binding
agreements of the Lessee enforceable in accordance with their respective terms.

     d.  The Equipment and Software is personal property and when subjected to
use by the Lessee will not be or become fixtures under applicable law.

     e.  Lessee shall furnish, upon request by Lessor, audited financial
statements for the most recent period.

X.   Title and Location
     ------------------

     Nothing contained in any Order shall give or convey to Lessee any right,
title or interest in or to the Equipment or Software, except as a Lessee as set
forth therein and Lessee represents and agrees that Lessee shall hold the
Equipment and Software subject and subordinate to the rights of Lessor, and
Lessee shall furnish Lessor with such documentation as Lessor shall reasonably
require with respect thereto.

     Lessor is hereby authorized by Lessee, at Lessee's expense, to cause this
Agreement, any Order, or any statement or other instrument in respect of any
Order as may be required or permitted by law showing the interest of Lessor, in
the Equipment or Software to be filed and Lessee appoints Lessor as its
attorney-in-fact to execute and file on behalf of Lessee, at Lessee's expense,
any UCC financing statements and amendments Lessor deems advisable to secure the
interests of Lessor. Without limiting the foregoing, Lessee shall execute one or
more financing statements, in form and

                                      -5-
<PAGE>
 
substance satisfactory to Lessor, covering all Equipment or Software leased
to Lessee pursuant to this Agreement.  The parties have agreed that a
photographic copy or other reproduction of this Agreement, either together with
or in lieu of an appropriate form under the UCC, is sufficient as a financing
statement for purposes of filing and perfection under the UCC.  Any filing of
such financing statements or any public recordation of this Agreement is
intended by the parties solely to protect the interest to Lessor and Lessee, and
no such filing or recordation shall in any manner imply or be construed as
implying that the relationship of Lessor to Lessee with respect to this
Agreement or to the Equipment or Software is anything other than that of a
personal property Lessor to a personal property Lessee.

     Lessee shall request Lessors consent, in writing, at least fifteen (15)
days before Lessee intends to move any of the Equipment or Software from its
original "ship to" location.  Lessors response to such request shall be in
writing and shall not be unreasonably withheld.  Lessee agrees to provide Lessor
with fifteen (15) days written notice of its intention to change its name or
corporate identity or structure, by merger, consolidation, reorganization or
otherwise.  In the event Lessee fails to comply with this paragraph or the
preceding paragraph, Lessee agrees to indemnify Lessor for any losses or damages
Lessor incurs thereby.

     Lessee shall, at its expense, protect and defend Lessors title against all
persons claiming against or through Lessee and shall at all times keep the
Equipment or Software free and clear from any legal process, liens or
encumbrances whatsoever (except any placed thereon by Lessor or person or entity
                                                             -------------------
claiming through Lessor) and shall give Lessor immediate written notice thereof
- -----------------------                                                        
and shall indemnify and hold Lessor harmless from and against any loss caused
thereby.

XI.  Lessor's Ownership Rights
     -------------------------

     The Equipment and Software shall at all times remain the property of
Lessor.  Lessee covenants and agrees that, upon the request of Lessor, it shall
cause the Equipment and Software to remain labeled as a Lessor unit of Equipment
or Software.  Lessee shall replace any such stenciling, tag or plate which may
be removed or destroyed or become illegible.  Lessee shall keep all Equipment
and Software free from any marking or labeling which might be interpreted as a
claim of ownership thereof by Lessee or might be interpreted as a claim or
anyone so claiming through Lessor.

XII. Binding Nature
     --------------

     Each Order shall be binding upon and shall inure to the benefit of Lessor,
Lessee and their respective successors, legal representatives and assigns.

XIII. Installation
      ------------

     Lessor is to install Equipment or Software, Lessee shall, in addition to
                                                               --------------
being liable for Lessors installation rates in effect at time of order, have the
- ----------------------------------------------------------------------          
site prepared prior to the beginning of the installation period at Lessee's
                                                                -----------
expense.  Installation will be scheduled Monday through Friday (excluding Lessor
- -------                                                                         
holidays), 8:00 a.m. to 6:00 p.m., local time.  "After Hours" installation is
available

                                      -6-
<PAGE>
 
and if requested by Lessee, Lessor will respond with a quotation for such
installation. Lessee shall provide timely computer programming support, if
required, during installation at no charge to Lessor. Preparation shall be in
accordance with Lessors installation site preparation specifications.  Lessor
shall install the Diagnostic Controller (if applicable).

XIV. Warranty and Remedy
     -------------------

     Lessor warrants all Equipment obtained hereunder to be free from defects in
material and workmanship in normal service and under normal conditions for one
(1) year from date of the initial invoice, and further, that the Equipment
obtained under the initial order hereunder is fit for the purposes described in
the Data Network Description attached hereto as Exhibit 3 and conforms to the
standard specifications at the time of the Order.  THE FOREGOING WARRANTY IS IN
LIEU OF ALL OTHER WARRANTIES EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING
WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.  THIS WARRANTY
IS VOID AS TO EQUIPMENT AND SOFTWARE LOCATED OUTSIDE OF THE UNITED STATES OF
AMERICA.

     Should a unit of Equipment, which is not subject to an effective Lessor
                                 -------------------------------------------
maintenance agreement fail in normal service and under normal conditions through
- ---------------------                                                           
no fault of the Lessee during the warranty period, Lessee shall return the
failed unit at Lessor's expense to Lessor's point of origin facility.  Lessor
shall either repair the unit at the factory or furnish a used, refurbished
replacement unit for the Lessee.  No charges will be made for repair or
replacement.  Lessee shall connect and adjust the unit in accordance with
accompanying instructions.  Each repaired or replacement unit of equipment is
warranted (as set forth above) for sixty (60) days from the date of shipment of
such repaired unit, or the remaining portion of the original Equipment's
warranty, whichever is longer. Lessee agrees to pay Lessor's then standard time
and material charges for repairs made outside of those covered by the Warranty.
For any nonconformance of the Software (if applicable) to its specification
which affects performance and is reported to Lessor by Lessee, in writing,
during the initial ninety (90) days following deployment, Lessor shall provide
an analysis of the problem and workable solution.  For Software nonconformances
                                                   ----------------------------
which are recorded in writing to Lessor by Lessee subsequent to the
- -------------------------------------------------------------------
aforementioned ninety (90) day Software warranty period, Lessee agrees to pay
- -------------------------------------------------------                      
Lessors then current Software charges for analysis and efforts to obtain
workable solutions provided outside of those covered by the Warranty.  Lessee
agrees that it will in no event, alter, modify, repair, disassemble, or adjust
the Equipment or Software obtained hereby, except in accordance with Lessor
instructions. Lessor's obligations hereunder are contingent upon proper storage,
installation, use and maintenance and are limited to:  (1) repair, or at its
option, replacement (as described herein above) of any parts or Equipment when
the parties agree that the Equipment does not conform to the Warranty; (2)
analyzing and providing a workable solution to Software problems when Lessor
determines that the nonconformance significantly affects performance in
accordance with standard specifications and the specifications required pursuant
to Exhibit A; (3) termination of the lease and if the remedy provided for herein
has failed of its essential purpose, recovery of such damages as provided for
herein by the Lessee.  Maintenance of Software, as used herein, is the
implementation by Lessee of Software revisions provided by Lessor.  Revisions
consist of improvements of specified programs.  THE FOREGOING CONSTITUTES
LESSEE'S SOLE

                                      -7-
<PAGE>
 
AND EXCLUSIVE REMEDY AND IS IN LIEU OF ANY AND ALL OTHER REMEDIES WHICH MAY BE
AVAILABLE TO LESSEE.

XV.  Care, Use and Maintenance
     -------------------------

     Lessee shall, at its sole expense, at all times during the term of each
Order, maintain the Equipment and Software in good operating order, repair,
condition and appearance and protect the Equipment and Software from
deterioration, other than normal wear and tear.  Lessee shall not use the
equipment or Software for any purpose other than that for which it was designed.
Lessee shall, at its sole expense, enter into and maintain in force, for the
term of each Order, a maintenance agreement.

XVI. Software License
     ----------------

     a.  Lessor hereby grants to Lessee a revocable, nonexclusive license
to uses copy of the Software in object code form, and only on a singly
designated processing unit for Lessee's own internal use, except that Lessee may
execute the Software on another processing unit on a temporary basis during a
malfunction which prevents execution of the Software on the existing processing
unit. Lessee agrees not to copy Software in whole or in part without the written
consent of Lessor except Lessee may maintain an archival copy of the Software
for back-up purposes.  Lessee agrees to reproduce any copyright and/or
confidentiality notices on any copy of the Software or any portion thereof made
by Lessee.  Additional copies of Software required by Lessee for its use must be
licensed from Lessor.

     b.  Lessee agrees to maintain complete and accurate records which identify
the type and location of the Software.  Within thirty (30) days after receiving
a request from Lessor, Lessee shall provide copies of the applicable records to
Lessor.

     c.  Lessor warrants the Software obtained hereunder shall conform to its
standard specifications and to the specifications required according to Exhibit
3 at the time that it is received by Lessee.

     d.  Title to the Software shall not pass to Lessee.  This license may not
be assigned, sublicensed, or otherwise transferred by Lessee, except that Lessee
may transfer the license to a transferee and such transferee will have the sole
benefit of the Software as transferred from Lessee provided that Lessee gives
Lessor prior written notice of such transfer and transferee agrees in writing to
be bound under this license to the same degree as Lessee.

     e.  The term of an individual units license shall be from the date of
Lessor's acceptance of an individual Order for Software until expiration of the
term set forth on the face of the individual Order or upon any default of Lessee
of any term, covenant or obligation under this Agreement.  This license may be
renewed for additional one (1) or multiple year terms provided both parties
agree to such renewal in writing at least sixty (60) days prior to the
expiration of the initial term or renewal term.  Such renewal shall be in
accordance with Lessor's standard pricing policies in effect at time of

                                      -8-
<PAGE>
 
renewal.  Lessee agrees that upon termination or expiration of term of
individual Orders placed under license, Lessee will discontinue use of the
Software and shall certify in writing within three (3) days of termination of
this license that the Software and all copies thereof have been returned to
Lessor or destroyed.

     f.  If Lessee exercises the purchase conversion (set forth in Article
         -----------------------------------------------------------------
XXXVII below) the Software license granted to Lessee herein shall remain in
- ---------------------------------------------------------------------------
effect pursuant to the terms and conditions set forth herein.
- ------------------------------------------------------------ 

     g.  Lessee acknowledges that the Software supplied by Lessor constitutes
Lessors trade secrets and agrees to treat all Software as confidential and
proprietary.

     h.  Lessee shall not, without prior written permission of Lessor, transfer,
disclose or otherwise provide the programs to any person outside of Lessee's
organization.

     i.  Lessee shall not, without prior written permission of Lessor, modify,
reverse assemble or reverse compile any of the Software.

     j.  Lessee agrees that it shall thoroughly safeguard the confidentiality of
the Software supplied by Lessor, and in no event shall it be to a lesser extent
that Lessee safeguards its own proprietary information. Lessee agrees that
access to such Software will be given only to employees who require access in
the course of Lessee's business and such employees will be informed of the
confidential nature thereof and will be required to observe provisions of
confidence as set forth herein.

XVII. Software
      --------

     Lessor has no responsibility as to the unauthorized or improper, misuse or
     --------------------------------------------------------------------------
misapplication of the Software.  Lessee assumes full responsibility for data
- ------------------------------                                              
entry, data maintenance and the functional adequacy of the Software in meeting
Lessee's requirements except as provided herein, where the Software does not
conform to the specifications required by Exhibit 3.

XVIII. Taxes and Fees
       --------------

     Lessee covenants and agrees to pay when due or reimburse and indemnify and
hold Lessor harmless from and against all taxes, fees or other charges of any
nature whatsoever (together with any related interest or penalties not arising
from negligence on the part of Lessor) now or hereafter imposed or assessed
against Lessor, Lessee or the Equipment or Software by any Federal, state,
county or local governmental authority upon or with respect to the Equipment or
Software or upon the ordering, ownership, delivery, teasing, possession, use,
operation, return or other disposition thereof or upon the rents, receipts or
earnings arising therefrom or upon or with respect to any Order (excepting only
Federal, state and local taxes based on or measured by the net income of
Lessor).  If Lessee warrants that the Order shall be exempt from sales tax, it
is Lessee's responsibility to provide Lessor with valid sales tax exemption
certificates within thirty (30) days of date Order is placed.

                                      -9-
<PAGE>
 
Notwithstanding the foregoing, unless otherwise specified in the Order, Lessor
shall be responsible for the filing of all personal property tax returns in
respect to the Equipment or Software and shall pay all taxes indicated thereon.
Lessee shall reimburse Lessor for all such taxes within thirty (30) days of
receipt of Lessor's invoice therefor.  The final invoice for personal property
taxes with respect to the lease term may be issued subsequent to the expiration
of the term due to the nature and timing of notification by the state or local
governmental authority.

XIX. Purchase Orders
     ---------------

     If a Purchase Order is required for payment, Lessee agrees to provide the
applicable Purchase Order Number(s) to Lessor.  If no Purchase Order is required
for payment, Lessee guarantees that payment will not be delayed.

XX.  Force Majeure
     -------------

     Neither party shall be considered in default in performance of such
obligations is prevented or delayed by acts of God or government, labor
disputes, failure or delay of transportation, or by vendors of subcontractors,
or any other similar cause or causes beyond the reasonable control of the other
party.  Time of performance of either parties obligations hereunder shall be
extended by the time period reasonably necessary to overcome the effects of such
force majeure occurrences.

XXI. Patent Indemnity
     ----------------

     Lessor will defend, at as own expense, any action brought against Lessor's
Lessee to the extent that it is based upon a claim that Lessor provided
Equipment or Software, infringes any patent, trade secret or copyright and
Lessor will pay costs and monetary damages finally awarded against Lessor's
Lessee in any such actions which are attributable to such claim.

     Such defense and liability is conditioned on and limited by:  (a) Lessor
being notified promptly in writing by Lessee of any such action; (b) Lessor
having sole control of the defense and all negotiations for settlement of such
action: Lessee providing all available information, assistance and authority to
enable Lessor to defend, negotiate and settle such action.

     Should such Equipment or Software become, or in Lessors opinion be likely
to become, the subject to a claim of infringement or the use thereof become
restricted by a final non-appealable Court awarded injunction, the Lessee shall
permit Lessor, at Lessor's option and expense, the right to either: (a) procure
for the Lessee the right to continue using such Equipment or Software; (b)
replace or modify such Equipment or Software so it is free from infringement or
injunction provided that the same function is performed by the replacement or
modified Equipment or Software.  In the event that Lessor does not provide the
remedial action described in (a) or (b), then Lessor may recover such Equipment
or Software from the Lessee in which case, the only rights and liabilities
between Lessor and Lessee are that:  (i) the lease shall be void as to the
Equipment or Software on the date of recovery; and (ii) Lessor has the right to
collect lease payments, if any, due from the Lessee for the Lessee's possession
of such Equipment or Software up through the date of Lessors recovery thereof

                                      -10-
<PAGE>
 
or the date on which Lesee's use of such Equipment or Software is enjoined by a
court of competent jurisdiction whichever is earlier.

     Lessor shall have no liability to the Lessee under any provision of this
clause with respect to any claim or infringement which is based upon:

     a.  Equipment or Software based on specifications furnished by the Lessee,
or

     b.  the combination or utilization of Equipment or Software furnished
hereunder with Equipment or Software not provided by Lessor in accordance with
Exhibit 3, or

     c.  an unauthorized modification by the Lessee of Equipment or Software
         ---------------                                                    
furnished hereunder which affects the infringement.

     The foregoing expresses the entire liability of Lessor for patent or
copyright infringement by Lessor Equipment or Software to Lessee.

XXII. Default
      -------

     With the exception of a Default in the initial payment, which shall
constitute an immediate breach, failure of Lessee to make payments or to perform
any other condition of this Agreement or any Exhibit hereto, which shall
                            --------------------------------------------
continue for a period of fifteen (15) business days following written notice
- ----------------------------------------------------------------------------
thereof shall constitute breach of the affected Order(s) placed hereunder.  The
failure by Lessee, within sixty (60) days after the commencement of any
proceeding against Lessee seeking any reorganization, arrangement, composition,
readjustment, liquidation, dissolution, or similar relief under any present or
future statute, law, regulation, to obtain the dismissal of such proceeding or,
within sixty (60) days after the appointment, without the consent or
acquiescence of Lessee, of any trustee, receiver or liquidation of Lessee or of
all or any substantial part of the properties of Lessee to vacate such
appointment shall constitute a breach of all Orders placed hereunder.  In case
of breach, Lessor may cancel the defaulted Order(s) declare the entire amount of
the unpaid commitment and any other charges immediately due and payable and use
all available remedies to take possession and remove Equipment and Software with
all costs, including attorney's fees, to be borne by Lessee. Lessor's right to
recover possession of the Equipment and Software is in addition to all available
remedies at law or in equity.

XXIII. Severability
       ------------

     If any provision or provisions of this Agreement shall be held to be
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions shall not in any way be affected or impaired thereby,
provided such provision still expresses the intent of the parties. If the intent
of the parties cannot be preserved, the Agreement shall either be renegotiated
or rendered null and void.

                                      -11-
<PAGE>
 
XXIV. Limitation of Liability
      -----------------------

     LESSOR SHALL NOT BE LIABLE FOR ANY INDIRECT, INCIDENTAL, SPECIAL OR
CONSEQUENTIAL DAMAGES, INCLUDING BUT NOT LIMITED TO LOSS OF PROFITS OR REVENUE,
LOSS OR USE OF THE EQUIPMENT OR SOFTWARE OR ANY ASSOCIATED EQUIPMENT OF SOFTWARE
OR COST OF SUBSTITUTED FACILITIES, EQUIPMENT, SOFTWARE OR SERVICES WHICH ARISE
OUT OF PERFORMANCE OR FAILURE TO PERFORM ANY OBLIGATION CONTAINED WITHIN THIS
AGREEMENT, OR OUT OF NEGLIGENCE IN THE COURSE OF SUCH PERFORMANCE, WHETHER THE
CLAIM FOR DAMAGES IS BASED IN CONTRACT, TORT (INCLUDING NEGLIGENCE), STRICT
LIABILITY OR OTHERWISE.

     Except for claims for personal injury or for damage to real or tangible
personal property to the extent caused by Lessors fault or negligence, Lessors
maximum liability to Lessee for any claim for damages relating to Lessors
performance or nonperformance under this Agreement shall be limited to the
lesser of the amount of payments for Equipment and Software received by Lessor
at the time the cause of action accrued or $500,000.

XXV. Governing Law; Forum
     --------------------

     This Agreement shall be governed and construed in accordance with the laws
of the State of Florida.  The parties hereby consent and submit to the exclusive
jurisdiction of the appropriate state or federal court serving Broward County,
Florida, as to any dispute or controversy arising either directly or indirectly,
under or in connection with this Agreement.

XXVI. Waiver
      ------

     No waiver by either party of any default shall operate as a waiver of any
other default or of the same default on a future occasion.  No delay, course of
dealing or omission on the part of either party in exercising any right or
remedy shall operate as a waiver thereof, and no single or partial exercise by
either party of any right or remedy shall preclude any other or further exercise
thereof or the exercise of any other right or remedy.

XXVII. Insurance
       ---------

     Lessee shall, at its own expense, and at all times during the term of an
individual Order keep the Equipment and Software insured against all risks of
loss or damage from every cause whatsoever for not less than the then current
purchase price of the Equipment or Software, provided that the amount of such
insurance shall be sufficient so that neither Lessor nor Lessee shall be
considered a co-insurer.  Lessee shall also carry public liability insurance
covering both personal injury and property damage caused by the Equipment or
Software.  All such policies of insurance shall name Lessor as loss payee or
additional insured as the case may be.  Lessee shall deliver to Lessor a copy of
such Certificates of Insurance.  Each insurer shall agree by endorsement upon
each policy issued by it or by independent instrument furnished with such policy
to Lessor, that it shall give Lessor no less

                                      -12-
<PAGE>
 
than thirty (30) days written notice before any such policy shall be materially
altered or canceled Lessee hereby appoints Lessor as Lessee's attorney-in-fact
to make claim for, receive payment of, and execute and endorse all documents,
checks or drafts for loss or damage under any such policies of insurance

XXVIII. Risk of Loss
        ------------

     Lessee shall bear the entire risk of loss, theft, damage or destruction of
the Equipment and Software from any cause whatsoever (except Lessors negligence)
from the time shipment is received by Lessee until return shipment is received
in Sunrise, Florida by Lessor.

XXIX. Government Obligations
      ----------------------

     Lessee warrants that it is, and will remain, in compliance with all export
requirements, including, but not limited to, the requirements of the Export
Administration Act and regulations, the Arms Export Control Act and regulations,
and any orders and licenses issued thereunder.  Such requirements include, but
are not limited to, obtaining all proper authorizations or licenses from the
Department of Commerce or the Department of State for the export or re-export of
any item, product, article, commodity or technical data.  Lessee additionally
warrants that it has not been, and is not currently, debarred or suspended from
or otherwise prohibited or impaired from exporting, re-exporting, receiving,
purchasing, procuring, or otherwise obtaining any item, product, article,
commodity, or technical data regulated by any agency of the government of the
United States. Lessee agrees to indemnify Lessor and hold Lessor harmless from
any costs, penalties, or other losses caused by, or related to, any violation of
the warranties contained in this contract.

XXX. Intention of Parties
     --------------------

     It is the intention of Lessor and the Lessee that any lease Orders placed
under this Agreement will be characterized as "true leases" and not "financing
leases" or "leases intended for security".

XXXI. Custom Systems
      --------------

     Supplements to this Agreement, which include any specially-configured
systems are non-cancelable.  Once acknowledged, any changes in supplements which
include specially-configured systems will result in a minimum reconfiguration
charge by Lessor to Lessee of at least Five Hundred Dollars ($500).

XXXII. Compliance with Laws
       --------------------

     Lessee shall comply with all applicable laws, ordinances, rules and
regulations and Lessee shall obtain any and all permits, licenses,
authorizations and/or certificates that may be required in any jurisdiction or
by any regulatory or administrative agency in connection with the use and/or
operation of the Equipment or Software.

                                      -13-
<PAGE>
 
XXXIII. Quiet Enjoyment
        ---------------

     Lessor hereby agrees and covenants, so long as no default has occurred and
is continuing, that Lessee shall have, hold and quietly enjoy, subject to this
Agreement, the Equipment and every unit and part thereof during the term of this
Agreement.

XXXIV. Certificate of Deposit
       ----------------------

     As a condition precedent to Lessors obligations, including but not limited
to the acceptance of an Order hereunder, and as partial security for Lessee's
payment obligations hereunder, Lessee agrees to provide Lessor with a
Certificate of Deposit which shall be held in an escrow account pursuant to an
escrow agreement between the parties hereto.  Certain of the agreed upon
material terms of the proposed escrow agreement are set forth on Exhibit One,
attached hereto.

XXXV. Warrants in Stock
      -----------------

     As a further condition precedent to shipment of any product hereunder
Lessee and Lessor shall enter into an agreement pursuant to which Lessor shall
receive Warrants in Lessee's company stock.  Certain of the agreed upon material
terms of such agreement are set forth on Exhibit Two, attached hereto.

XXXVI. Leased Equipment Upgrade
       ------------------------

     Throughout the lease term of items of Equipment leased under this
Agreement, Lessee shall have the right to terminate the lease of individual
units of Equipment leased hereunder for the sole purpose of replacing such
Equipment with other Lessor Equipment.  Such terminations can be made only if
ALL of the following conditions are met:

     A.  The units of Equipment being terminated must have been on lease for at
least fifty percent (50%) of their original lease term; and,

     B.  The units of Equipment being terminated must have an original lease
term of twenty-four (24) months or longer; and,

     C.  Lessee shall provide at least sixty (60) days prior written notice to
Lessor to exercise this option; and,

     D.  The replacement Equipment must be leased for the same initial term as
the Equipment which is being replaced; and,

     E.  Replacement Equipment must be of equal or greater functionality and of
equivalent or greater Capital Value; and,

                                      -14-
<PAGE>
 
     F.  The total monthly lease and maintenance payments for the replacement
Equipment must be at least seventy percent (70%) of the total monthly lease and
                           ----------------------------                        
maintenance payments for the Equipment being terminated; and,

     G.  For all Equipment being terminated, all Amounts due and payable under
the lease, including monthly lease payments to the date of termination, and any
taxes, charges and fees which arise on or before the date of termination must be
paid in full; and,

     H.  If maintenance was taken on Equipment being terminated, maintenance
must be taken on replacement Equipment; and,

     I.  De-installation and installation by Lessor will be at standard Hourly
Labor rates, unless specified otherwise by contract; and,

     J.  The order must indicate it is an upgrade and must include all serial
numbers of Equipment to be terminated.

XXXVII.  Purchase Conversion
         -------------------

     Lessee shall at all times during the term of a lease order issued pursuant
to this Agreement have an option to purchase the Equipment leased hereunder by
paying Lessor the purchase conversion price.  The purchase conversion price
shall be an amount equal to the unit purchase price set forth on the face of the
Lessor's Order Form or Lessee's Order form, reduced by fifty percent (50%) of
all lease payments paid applicable to the unit which is being converted to
purchase. However, in no event shall the purchase conversion price be less than
twenty percent (20%) of the unit purchase price set forth on the face of the
Lessors Order Form or Lessee's Order Form or the remaining lease obligation.
Exercise of this option shall in no way relieve Lessee for lease payments due up
to the date of conversion, but not yet paid, on the unit which is being
converted to purchase.

     In addition, Lessee shall have an option, upon expiration of the initial
     ------------------------------------------------------------------------
lease term, to Purchase the Equipment leased hereunder by paying Lessor the
- ---------------------------------------------------------------------------
purchase conversion price.  The Purchase conversion price shall be twenty
- -------------------------------------------------------------------------
percent (20%) of the unit purchase price set forth on the face of the Lessors
- -----------------------------------------------------------------------------
Order Form or Lessee's Order form.  Exercise of this option shall in no way
- ---------------------------------------------------------------------------
relieve Lessee for lease payments due up to the date of conversion, but not yet
- -------------------------------------------------------------------------------
paid on the unit which is being converted to purchase.
- ----------------------------------------------------- 

XXXVIII. Board of Directors
         ------------------

     As a condition precedent to Lessor's obligation to accept an order and/or
ship equipment or software hereunder, the parties have agreed that they shall
have executed a side letter pursuant to which Lessor shall have the option of a
seat on the Lessee's board of directors.

                                      -15-
<PAGE>
 
XXXIX. Further Assurances
       ------------------

     As a condition to Lessor's performance hereunder or any Order placed
pursuant hereto, Lessee agrees that it shall furnish such financial reporting
documents to Lessor on a quarterly basis, such financial reports shall include
but not limited to audited financial statements and certificates of acceptance.

XL.  Notices
     -------

     Any notices or communications given or required under this Agreement shall
     --------------------------------------------------------------------------
be sufficiently given if delivered personally in writing, or sent by telex or
- -----------------------------------------------------------------------------
facsimile, federal express, registered or certified mail, postage prepaid, to
- -----------------------------------------------------------------------------
the other party at the following address:
- ---------------------------------------- 

     TO:  Racal-Datacom, Inc.
          P.O. Box 407044
          Ft. Lauderdale, Florida 33340
          Attn:  Sr. Vice President and General Counsel


     TO:  Concentric Research Corporation
          400 Forty-First Street
          Bay City, Michigan 48708
          Attn:  President

     With a copy to:
          Susan Cook, Esq.
          Lambert, Leser, Cook, Schmidt & Giunta, P.C.
          309 Davidson Building, P.O. Box 835
          Bay City, Michigan 48707

     Such notice or other communications shall be deemed received (a) on the
     -----------------------------------------------------------------------
date delivered, if delivered personally; or (b) upon receipt, if sent by telex
- ------------------------------------------------------------------------------
or facsimile federal express or (c) three (3) business days after being sent, if
- --------------------------------------------------------------------------------
sent registered or certified mail.
- --------------------------------- 

XLI.  Maintenance Agreement
      ---------------------

     As a condition precedent to Lessor's and Lessee's obligation to accept an
order and/or ship product hereunder, the parties shall have executed and
delivered a maintenance agreement which provides for the first year of its term,
free maintenance between them respecting equipment and software purchased
hereunder.

                                      -16-
<PAGE>
 
XLII.  Entire Agreement
       ----------------

     The terms and conditions contained in this Agreement and the referenced
                                                                  ----------
Exhibits which are hereby incorporated herein shall be applicable to all Orders
- ---------------------------------------------                                  
placed on Lessor by Lessee during the effectiveness of this Agreement whether
referenced or not on such Orders.  Additional or different terms contained in
Lessee's purchase orders shall not be applicable to such Orders unless expressly
agreed to in writing by Lessors authorized representative.  This Agreement,
including all Orders accepted hereunder, expresses the entire understanding and
agreement of the parties with reference to the subject matter hereof, and is a
complete and exclusive statement of the terms of this Agreement, and no
representations or agreements modifying or supplementing the terms of this
Agreement shall be valid unless in writing, signed by persons authorized to sign
agreements on behalf of both parties.


     IN WITNESS WHEREOF, this Agreement was entered into as of the day and year
first written above.


ACCEPTED:  CONCENTRIC RESEARCH CORP.     ACCEPTED:  RACAL-DATACOM. INC.
           -------------------------                --------------------------

LESSEE:  /s/ Mark Collins-Rector         LESSOR  /s/ Scott A. Thomas
         ---------------------------             -----------------------------

BY:  Mark Collins-Rector                 BY:  Scott A. Thomas
     -------------------------------          --------------------------------

TITLE:  CEO                              TITLE:  District Sales Manager
        ----------------------------             -----------------------------

DATE:  8/4/94                            DATE:  8/4/94
       -----------------------------            ------------------------------

                                      -17-
<PAGE>
 
                                  EXHIBIT ONE

                    CERTIFICATE OF DEPOSIT/LETTER OF CREDIT


     A Certificate of Deposit shall be:  (i) provided by a mutually agreed upon
third party at least ten (10) days order to the initial shipment hereunder, (ii)
               -----------------------------------------------------------      
in an amount of $500,000 or 12.5% of the initial Order placed hereunder,
whichever is less (iii) placed in escrow pursuant to an escrow agreement to be
negotiated between the parties.  Lessee may replace the security at any time
with a Certificate of Deposit or Letter of Credit issued by Lessee in a form
                                                                   ---------
acceptable to Lessor.  The Certificate of Deposit may be released or replaced by
- --------------------                              ------------------------------
Lessee when all of the following conditions am obtained by Lessee and
- ---------------------------------------------------------------------
satisfactorily demonstrated to Lessor:
- ------------------------------------- 

     a.  Lessee's net worth exceeds $3,155,000; and
         ------------------------------------------

     b.  current ratio exceeding 2:1' and
         --------------------------------

     c.  no defaults or violations of loan covenants exist on outstanding debts
         ----------------------------------------------------------------------
of Lessee; and
- --------------

     d.   Lessor has been paid on all balances owed to Lessor.
          --------------------------------------------------- 

                                      -18-
<PAGE>
 
                                  EXHIBIT TWO

                               WARRANTS IN STOCK


     Warrants issued to Lessor for the initial order hereunder shall equal ten
                                                                     -----    
percent (10%) of the Equipment Gross Lease Value.  The option price of the
                                                   -----------------------
Warrants issued shall be $1.00 per share. Lessor agrees to exercise said
- ------------------------                                                
warrants at any time, or from time to time as it may in its sole discretion
- ---------------------------------------------------------------------------
decide, within forty-eight (48) months from date of issue; after said forty-
- -------------------------------                                       -----
eight (48) months, said warrants shall expire.
- ----------                                    

     The parties agree to enter into a mutually agreeable Warrants Agreement
         -------------------------------------------------------------------
prior to shipment of any Equipment hereunder.
- -------------------------------------------- 

                                      -19-
<PAGE>
 
                                   EXHIBIT 3

                            DATA NETWORK DESCRIPTION

     The communication system engineered by R-D is designed to provide Customer
consumers with asynchronous dial-in connectivity to Customer supported
applications and access gateways.

     The communication system as designed, provides consumer access to Customer
remote data services through the interconnection of telco circuits provisioned
by or through either a Wide Area Network provider (e.g. AT&T and/ or Racal,
whichever provides such service) or a local exchange carrier (i.e., Ameritech)
hereinafter referred to as the WAN provider.

     The WAN provider will aggregate the inbound calls and provide a total of 24
calls per T-1 connection.  The R-D ASET-1 product has been designed to support
incoming calls from asynchronous dial-up users at speeds ranging from 300 to
14,400 bps on an aggregate T-1 circuit supplied by the WAN provider.  While the
ASET-1 product was designed primarily to support aggregate incoming point of
sale transactions, outbound calls can also be initiated through the terminal
server connected to the ASET-1 chassis at the current supported speeds.

     The Customer consumer (herein dial-in user) will initiate a call through
their modem to the R-D ASET-1 product (or functionally equivalent) which will
establish a call path to an interconnected terminal server.  The Terminal Server
will establish a session via IR.  The IP traffic will be muted through the AT&T
Interspan (Frame Relay Network) by a router to Customers data center.

     The WAN providers network infrastructure will transport the user traffic to
the R-D T1 CSU and central site routers (located in the Customer data center)
where it will route the IP traffic onto the Customer local area network (LAN)
for communication to the Customer host(s).

     The R-D Equipment will provide outbound IP connectivity from the Customer
host(s) to the other data centers (hosts such as SBSs information providers,
corporate data centers, etc.) connected to the WAN providers network using R-D
provided Equipment.

                                      -20-
<PAGE>
 
                                  Performance

     The level of service provided by the WAN providers network (i.e., Frame
Relay network) will vary and is contingent upon such things to include (but not
limited to) actual system use/load, level of usage, and the bandwidth or
committed information rate (CIR) purchased by Customer. Network response times
may by adversely affected if insufficient bandwidth is purchased or network
usage exceeds application operational thresholds.

     R-D, working in concert and in cooperation with the WAN Provider and
Customer, will jointly determine the cause of problems which adversely affect
the network, utilization levels must be monitored on a regular basis by Customer
staff and the WAN Provider.  R-D will monitor the network performance throughout
the course of the installation process and will suggest and advise Customer as
to the need for remedial action necessary to maintain peak performance.

     The level of service (performance) as perceived by the network users will
depend upon many factors, some of those factors are listed below:

     1.   The bit rate of the network user's dial-up connection will directly
affect the data transfer rate.  A faster connection will naturally allow a
greater amount of data to be transported in a shorter period of time.  R-D will
make every effort to ensure that its' Equipment is able to connect to the
network users at the fastest rate possible based upon equipment readily
available to network users in the commercial marketplace and that such equipment
will meet generally agree upon standards of speed/operation (such as CCITT
specifications).

     2.   The use of error correcting modems such as MNP, V.42 bis, V-fast
protocols and speed will improve the level of service provided to the network
user by detecting telephone line induced errors and retransmitting the network
users' data.  Error correction functionality may introduce some delay when
errors are detected which result in the retransmission of data.  R-D's Equipment
will conform to generally accepted levels of service as demonstrated by
competitive modems accomplishing the same task.

     3.   High network utilization of a particular network access point or point
of presence POP) may affect the level of service perceived by the network users.
The speed of the link in to the WAN provider's network must offer sufficient
capacity to provide consistent and adequate response times.

     4.   Network users connecting via SLIP or PPP may put a greater load on the
network and R-D Equipment.

                                      -21-
<PAGE>
 
                                   EXHIBIT 4 

                                      -22-
<PAGE>
 
CRC - Dial in POP, 10 Modem Site (50 sites)
<TABLE> 
<CAPTION> 
                                                                                                                       Ship
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    Date
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A     1   Excalibur Card Carrier  excs2plus-2ac       D    2,850       2,850       2,423         19             0    9/30/94*
  B     1   System Controller       asetsyscon1a        A    2,400       2,400       2,040         19             0    9/30/94*
  C     1   T-1 CSU                 exaset1csu1         A    2,650       2,650       2,253         20           100    9/30/94*
  D     1   Aset Personality Mod.   Asetpermod          B      700         700         595          6             0    9/30/94*
  E     1   Aset Mster Control Pnl. Aset1mcp            B      800         800         680          0             0    9/30/94*
  F     5   Dual Modec              dfmodec232          A    2,250      11,250       8,563         90           500    9/30/94*
  G     1   Terminal Server         ILNTS-16c-110       A    2,995       2,995       2,546         30           180    9/30/94*
  H     1   TCP Featurepak          DKNTSTCPFC          A      495         495         421          0             0    9/30/94*
  I     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  J     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  K     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  L     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695       2,695       2,291         18           160    9/30/94*
  M     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*
  N     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  O     1   Rack Configured         C35-01BXXXX         D    2,258       2,258       1,919                             9/30/94*
  P     1   Outlet Power Strip      AC16AMP24           D      112         112          95                             9/30/94*
  Q     1   Fan Assembly            RKFAN               D      162         162         138                             9/30/94*
  R     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  S     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  T     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  U     1   IL Rackmount            IL Rack MB          D       35          35          64                             9/30/94*

                                                         Subtotal       35,388      30,117        266         1,420
Cables
  A    12   NTS to DCE              5956-176B-XX                50         600         600                             9/30/94*
  D     1   DCE Cable               5956-178C-XX                50          50          50                             9/30/94*
  B     1   T-1 CSU to Demarc       5956-840R-XX                50          50          50                             9/30/94*
  C     1   Personality to Edm      5956-743B-XX        D       50          50          50                             9/30/94*
  D     1   T-1 CSU to Edm          5956-158V-XX        D       20          20          20                             9/30/94*
  E     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  F     0   CS Daisy Chain          5956-743A-02        D       50           0           0                             9/30/94*
  G     1   Thin Net Segment        NA2020-20           D       30          30          30                             9/30/94*
  H     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  I     2   Thin T Connectors       NA2033              D       10          20          20                             9/30/94*
  J     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  K     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
  M     1   EDM to NTS              5956-178A-XX                50          50          50                             9/30/94*
  N     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*

                                                         Subtotal        1,420       1,420

                                                         Site Total     36,606      31,537
                                                                                            Mo. Maint  Install Total
                                                         Total       1,540,400   1,576,850     13,300        71,000
</TABLE> 

<PAGE>
 
CRC - Dial in POP, 16 Modem Site (18 sites)
<TABLE> 
<CAPTION> 
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             
  A     1   Excalibur Card Carrier  excs2plus-2ac       D    2,850       2,850       2,423         19             0    9/30/94*
  B     1   System Controller       asetsyscon1a        A    2,400       2,400       2,040         19             0    9/30/94*
  C     1   T-1 CSU                 exaset1csu1         A    2,650       2,650       2,253         20           100    9/30/94*
  D     1   Aset Personality Mod.   Asetpermod          B      700         700         595          6             0    9/30/94*
  E     1   Aset Mster Control Pnl. Aset1mcp            B      800         800         680          0             0    9/30/94*
  F     8   Dual Modec              dfmodec232          A    2,250      18,000      15,300        144           800    9/30/94*
  G     2   Terminal Server         ILNTS-16c-110       A    2,995       5,990       5,092         60           180    9/30/94*
  H     1   TCP Featurepak          DKNTSTCPFC          A      495         495         421          0             0    9/30/94*
  I     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  J     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  K     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  L     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695       2,695       2,291         18           160    9/30/94*
  M     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*
  N     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  O     1   Rack Configured         C35-01BXXXX         D    2,258       2,258       1,919                             9/30/94*
  P     1   Outlet Power Strip      AC16AMP24           D      112         112          95                             9/30/94*
  Q     1   Fan Assembly            RKFAN               D      162         162         138                             9/30/94*
  R     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  S     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  T     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  U     2   IL Rackmount            IL Rack MB          D       35          70          60                             9/30/94*

                                                         Subtotal       45,168      38,393        350         1,720
Cables
  A    17   NTS to DCE              5956-176B-XX                50         850         850                             9/30/94*
  D     1   DCE Cable               5956-178C-XX                50          50          50                             9/30/94*
  B     1   T-1 CSU to Demarc       5956-840R-XX                50          50          50                             9/30/94*
  C     1   Personality to Edm      5956-743B-XX        D       50          50          50                             9/30/94*
  D     1   T-1 CSU to Edm          5956-158V-XX        D       20          20          20                             9/30/94*
  E     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  F     0   CS Daisy Chain          5956-743A-02        D       50           0           0                             9/30/94*
  G     2   Thin Net Segment        NA2020-20           D       25          50          50                             9/30/94*
  H     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  I     3   Thin T Connectors       NA2033              D       10          30          30                             9/30/94*
  J     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  K     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
  M     2   EDM to NTS              5956-178A-XX                50         100         100                             9/30/94*
  N     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*

                                                         Subtotal        1,750       1,750

                                                         Site Total     46,918      40,143
                                                                                            Mo. Maint  Install Total
                                                         Total         844,524     722,574      6,300        30,960
</TABLE> 
<PAGE>
 
CRC - Dial in POP, 24 Modem Site (11 sites)
<TABLE> 
<CAPTION> 
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             
  A     1   Excalibur Card Carrier  excs2plus-2ac       D    2,850       2,850       2,423         19             0    9/30/94*
  B     1   System Controller       asetsyscon1a        A    2,400       2,400       2,040         19             0    9/30/94*
  C     1   T-1 CSU                 exaset1csu1         A    2,650       2,650       2,253         20           100    9/30/94*
  D     1   Aset Personality Mod.   Asetpermod          B      700         700         595          6             0    9/30/94*
  E     1   Aset Mster Control Pnl. Aset1mcp            B      800         800         680          0             0    9/30/94*
  F    12   Dual Modec              dfmodec232          A    2,250      27,000      22,950        216         1,200    9/30/94*
  G     2   Terminal Server         ILNTS-16c-110       A    2,995       5,990       5,092         60           180    9/30/94*
  H     1   TCP Featurepak          DKNTSTCPFC          A      495         495         421          0             0    9/30/94*
  I     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  J     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  K     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  L     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695       2,695       2,291         18           160    9/30/94*
  M     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*
  N     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  O     1   Rack Configured         C35-01BXXXX         D    2,258       2,258       1,919                             9/30/94*
  P     1   Outlet Power Strip      AC16AMP24           D      112         112          95                             9/30/94*
  Q     1   Fan Assembly            RKFAN               D      162         162         138                             9/30/94*
  R     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  S     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  T     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  U     2   IL Rackmount            IL Rack MB          D       35          70          60                             9/30/94*

                                                         Subtotal       54,168      46,043        389         1,860
Cables
  A    25   NTS to DCE              5956-176B-XX                50       1,250       1,250                             9/30/94*
  D     1   DCE Cable               5956-178C-XX                50          50          50                             9/30/94*
  B     1   T-1 CSU to Demarc       5956-840R-XX                50          50          50                             9/30/94*
  C     1   Personality to Edm      5956-743B-XX        D       50          50          50                             9/30/94*
  D     1   T-1 CSU to Edm          5956-158V-XX        D       20          20          20                             9/30/94*
  E     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  F     0   CS Daisy Chain          5956-743A-02        D       50           0           0                             9/30/94*
  G     2   Thin Net Segment        NA2020-20           D       25          50          50                             9/30/94*
  H     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  I     2   Thin T Connectors       NA2033              D       10          20          20                             9/30/94*
  J     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  K     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
  M     1   EDM to NTS              5956-178A-XX                50          50          50                             9/30/94*
  N     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*

                                                         Subtotal        2,090       2,090

                                                         Site Total     56,258      48,133
                                                                                            Mo. Maint  Install Total
                                                         Total         618,838     529,463      4,279        20,460
</TABLE> 


<PAGE>
 
CRC - Dial in POP, 32 Modem Site (6 sites)
<TABLE> 
<CAPTION> 
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>  <C>   <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A     2   Excalibur Card Carrier  excs2plus-2ac       D    2,850       5,700       4,845         38             0    9/30/94*
  B     2   System Controller       asetsyscon1a        A    2,400       4,800       4,080         38             0    9/30/94*
  C     2   T-1 CSU                 exaset1csu1         A    2,650       5,300       4,505         40           100    9/30/94*
  D     2   Aset Personality Mod.   Asetpermod          B      700       1,400       1,190         12             0    9/30/94*
  E     1   Aset Mster Control Pnl. Aset1mcp            B      800         800         680          0             0    9/30/94*
  F    16   Dual Modec              dfmodec232          A    2,250      36,000      30,600        288         1,600    9/30/94*
  G     1   3Slot Chassis           INX5000TR3C110      A    2,550       2,550       2,168         26           153    9/30/94*
  H     3   NTS Telco               NTSTELCOEK          A    2,485       7,485       6,362         75           450    9/30/94*
  I     1   TCP Featurepak          NTS-TCP-FC                 295         295         251          0             0    9/30/94*
  J     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220
  K     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  L     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  M     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695       2,695       1,785         18           160    9/30/94*
  N     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*
  O     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  P     1   Rack Configured         C35-01BXXXX         D    2,258       2,258       1,919                             9/30/94*
  Q     1   Outlet Power Strip      AC16AMP24           D      112         112          85                             9/30/94*
  R     1   Fan Assembly            RKFAN               D      162         162         138                             9/30/94*
  S     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  T     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  U     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  V     1   INX Rackmount Shelf     INX Rack MS         D      125         125          60                             9/30/94*

                                                         Subtotal       75,668      64,318        566         2,683
Cables
  A     5   NTS to DCE              5956-139T-XX               160         800         800                             9/30/94*
  B     1   NTS to DTE              5956-139R-XX               160         160         160                             9/30/94*
  C     2   T-1 CSU to Demarc       5956-840R-XX                50         100         100                             9/30/94*
  D     2   Personality to Edm      5956-743B-XX        D       50         100         100                             9/30/94*
  E     2   T-1 CSU to Edm          5956-158V-XX        D       20          40          40                             9/30/94*
  F     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  G     1   CS Daisy Chain          5956-743A-02        D       50          50          50                             9/30/94*
  H     1   Thin Net Segment        NA2020-20           D       25          25          25                             9/30/94*
  I     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  J     2   Thin T Connectors       NA2033              D       10          20          20                             9/30/94*
  K     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  L     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
  N     1   EDM to NTS              5956-146U-XX                50          50          50                             9/30/94*
  B     1   PC to EDM/DDM/SDM       5956-146W           D       50          50         100                             9/30/94*
  O     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*

                                                         Subtotal        1,945       1,995

                                                         Site Total     77,613      66,313
                                                                                            Mo. Maint  Install Total
                                                         Total         388,065     331,565      2,830        13,415
</TABLE> 


<PAGE>
 
CRC - Dial in POP, 40 Modem Site (3 sites)
<TABLE> 
<CAPTION> 
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             
  A     2   Excalibur Card Carrier  excs2plus-2ac       D    2,850       5,700       4,845         38             0    9/30/94*
  B     2   System Controller       asetsyscon1a        A    2,400       4,800       4,080         38             0    9/30/94*
  C     2   T-1 CSU                 exaset1csu1         A    2,650       5,300       4,505         40           100    9/30/94*
  D     2   Aset Personality Mod.   Asetpermod          B      700       1,400       1,190         12             0    9/30/94*
  E     1   Aset Mster Control Pnl. Aset1mcp            B      800         800         680          0             0    9/30/94*
  F    20   Dual Modec              dfmodec232          A    2,250      45,000      38,250        360         2,000    9/30/94*
  G     1   3Slot Chassis           INX5000TR3C110      A    2,250       2,550       2,168         26           153    9/30/94*
  H     3   NTS Telco               NTSTELCOEK          A    2,495       7,485       6,362         75           450    9/30/94*
  I     1   TCP Featurepak          NTS-TCP-FC          A      295         295         251          0             0    9/30/94*
  J     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  K     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  L     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  M     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695       2,695       2,291         18           160    9/30/94*
  N     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*
  O     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  P     1   Rack Configured         C35-01BXXXX         D    2,258       2,258       1,919                             9/30/94*
  Q     1   Outlet Power Strip      AC16AMP24           D      112         112          95                             9/30/94*
  R     1   Fan Assembly            RKFAN               D      162         162         138                             9/30/94*
  S     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  T     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  U     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  V     1   INX Rackmount Shelf     INX Rack MS         D      125         125         106                             9/30/94*

                                                         Subtotal       84,668      71,968        638         3,083    
Cables
  A     5   NTS to DCE              5956-139T-XX               160         800         800                             9/30/94*
  B     1   NTS to DTE              5956-139R-XX               160         160         160                             9/30/94*
  C     2   T-1 CSU to Demarc       5956-840R-XX                50         100         100                             9/30/94*
  D     2   Personality to Edm      5956-743B-XX        D       50         100         100                             9/30/94*
  E     2   T-1 CSU to Edm          5956-158V-XX        D       20          40          40                             9/30/94*
  F     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  G     1   CS Daisy Chain          5956-743A-02        D       50          50          50                             9/30/94*
  H     1   Thin Net Segment        NA2020-20           D       25          25          25                             9/30/94*
  I     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  J     2   Thin T Connectors       NA2033              D       10          20          60                             9/30/94*
  K     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  L     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
  N     1   EDM to NTS              5956-146U-XX                50          50          50                             9/30/94*
  B     1   PC to EDM/DDM/SDM       5956-146W           D       50          50         100                             9/30/94*
  O     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*

                                                         Subtotal        1,945       2,035

                                                         Site Total     86,613      74,003
                                                                                            Mo. Maint  Install Total
                                                         Total         259,839     222,009      1,914         9,249
</TABLE> 


<PAGE>
 
CRC - Dial in POP.48 Modem Site (4 sites)
<TABLE> 
<CAPTION> 
                                           
Item  Qty  Description               Part Number       Cat      List     Ext. Price   CRC Price  Ext. Maint  Ext. Install
<S>   <C>  <C>                       <C>               <C>      <C>      <C>          <C>        <C>         <C>            <C>
A      2   Excalibur Card Carrier    exes2plus-2sc      D       2,850     5,700         4,845         38            0       9/30/94*
B      2   System Controller         asetsyscon1s       A       2,400     4,800         4,080         38            0       9/30/94*
C      2   T-1 CSU                   exaset1csu1        A       2,650     5,300         4,505         40          100       9/30/94*
D      2   Aset Personality Mod.     Asetpermod         B         700     1,400         1,190         12            0       9/30/94*
E      1   Aset Mster Control Pnl.   Aset1mcp           B         800       800           680          0            0       9/30/94*
F     24   Dual Modec                afmodec232         A       2,250    54,000        45,900        432        2,400       9/30/94*
G      1   13Slot Chassis            INX5000TR13C110    A       4,250     4,250         3,613         43          255       9/30/94*
H      4   NTS Telco                 NTSTELCOEK         A       2,495     9,980         8,483        100          600       9/30/94*
I      1   TCP Featurepak            NTS-TCP-FC         A         295       295           251          0            0       9/30/94*
J      1   WAN Router                WF20002                    2,745     2,745         2,333         31          220       9/30/94*
K      1   AN Software               WF42021                        0         0             0          0            0       9/30/94*
L      1   Ethernet Trans Thin       U3-NT1000                    169       169           144                               9/30/94*
M      1   ISX 5300 Single DS1       ISX500SA-CMS-CS01  B       2,695     2,695         2,291         18          160       9/30/94*
N      1   EDM                       EDM115                     2,100     2,100         1,785         21          150       9/30/94*
O      1   3223 Class A              ALM3223                      749       749           637         12          110       9/30/94*
P      1   Rack Configured           C35-01BXXXX        D       2,258     2,258         1,919                               9/30/94*
Q      1   Outlet Power Strip        AC16AMP24          D         112       112            95                               9/30/94*
R      1   Fan Assembly              RKFAN              D         162       162           138                               9/30/94*
S      1   Fixed Shelf               SELFFIX19          D          73        73            62                               9/30/94*
T      1   Excal Rackmount           RKMT900            D          75        75            64                               9/30/94*
U      1   ALM3223 Rackmount         slimline-1         D          75        75            64                               9/30/94*
V      1   INX Rackmount Shelf       INX Rack MS        D         125       125           106                               9/30/94*
                                                                                                                            
                                                         Subtotal        97,863        83,184        752        3,735       
Cables
A      6   NTS to DCE                5956-139T-XX                 160       960           960                               9/30/94*
B      1   NTS TO DTE                5956-139R-XX                 160       160           160                               9/30/94*
C      2   T-1 CSU to Demarc         5956-840R-XX                  50       100           100                               9/30/94*
D      2   Personality to Edm        5956-743V-XX       D          50       100           100                               9/30/94*
E      2   T-1 CSU to Edm            5956-158V-XX       D          20        40            40                               9/30/94*
F      1   AUI Cable                 5956-840Z-XX       D          70        70            70                               9/30/94*
G      1   CS Daisy Chain            5956-743A-02       D          50        50            50                               9/30/94*
H      1   Thin Net Segment          NA2020-20          D          25        25            25                               9/30/94*
I      2   Thin Terminators          NA2034             D          30        60            60                               9/30/94*
J      2   Thin T Connectors         NA2033             D          10        20            20                               9/30/94*
K      1   ISX5300 v.35 stub cabl    5956-879 7                    80        80            80                               9/30/94*
L      1   CSU to EDM                5956-858V-XX                  20        20            20                               9/30/94*
N      1   EDM to NTS                5956-146U-XX                  50        50            50                               9/30/94*
B      1   PC to EDM/DDM/SDM         5956-146W          D          50        50           100                               9/30/94*
O      1   Rtr to DCE (v.35)         WF7220                       215       215           215                               9/30/94*
G      1   Rtr Consl to Term Svr     WF7526                       105       105           105                               9/30/94*

                                                         Subtotal         2,105         2,155 

                                                         Site Total      99,968        85,338
                                                                                               Mo. Maint  Install Total
                                                         Total          399,872       341,358      3,008         14,940
</TABLE> 
<PAGE>
 
CRC - Dial in POP, 52 Modem Site (1 site)
<TABLE> 
<CAPTION> 

Item   Qty  Description              Part Number        Cat List   Ext. Price  CRC Price  Ext. Maint.   Ext. Install
<S>    <C>  <C>                      <C>                <C> <C>    <C>         <C>        <C>           <C>           <C> 
 A      3   Excalibur Card Carrier   excs2plus-2sc       D  2,850    8,550      7,268      57              0         9/30/94*
 B      3   System Controller        asetsyscon1a        A  2,400    7,200      6,120      57              0         9/30/94*
 C      3   T-1 CSU                  exaset 1 csu1       A  2,650    7,950      6,758      60            100         9/30/94*
 D      3   Aset Personality Mod.    Asetpermod          B    700    2,100      1,785      18              0         9/30/94*
 E      1   Aset Mster Control Pnl.  Aset1mcp            B    800      800        680       0              0         9/30/94*
 F     26   Dual Modec               dfmodec232          A  2,250   58,500     49,725     468           2600         9/30/94*
 G      1   13Slot Chassis           INX5000TR13C110     A  4,250    4,250      3,613      43            255         9/30/94*
 H      4   NTS Telco                NTSTELCOEK          A  2,495    9,960      8,483     100            600         9/30/94*
 I      1   TCP Featurepak           NTS-TCP-FC          A    295      295        251       0              0         9/30/94*
 J      1   WAN Router               WF20002                2,745    2,745      2,333      31            220         9/30/94*
 K      1   AN Software              WF42021                    0        0          0       0              0         9/30/94*
 L      1   Ethernet Trans Thin      U3-NT1000                169      169        144                                9/30/94*
 M      1   ISX 5300 Single DS1      ISX500SA-CMS-CS01   B  2,695    2,695      2,291      18            160         9/30/94*
 N      1   EDM                      EDM115                 2,100    2,100      1,785      21            150         9/30/94*
 O      1   3223 Class A             ALM3223                  749      749        637      12            110         9/30/94*
 P      1   Rack Configured          C35-01BXXXX         D  2,258    2,258      1,919                                9/30/94*
 Q      1   Outlet Power Strip       AC16AMP24           D    112      112         95                                9/30/94*
 R      1   Fan Assembly             RKFAN               D    162      162        138                                9/30/94*
 S      1   Fixed Shelf              SELFFIX19           D     73       73         62                                9/30/94*
 T      1   Excal Rackmount          RKMT900             D     75       75         64                                9/30/94*
 U      1   ALM3223 Rackmount        slimline-1          D     75       75         64                                9/30/94*
 V      1   INX Rackmount Shelf      INX Rack MS         D    125      125        108                                9/30/94*

                                                        Subtotal   110,963     94,319     852          3,935  
Cables
 A      7   NTS to DCE               5956-139T-XX             160    1,120      1,120                                9/30/94*
 B      1   NTS to DTE               5956-139R-XX             160      160        160                                9/30/94*
 C      3   T-1 CSU to Demarc        5956-840R-XX              50      150        150                                9/30/94*
 D      3   Personality to Edm       5956-743B-XX        D     50      150        150                                9/30/94*
 E      3   T-1 CSU to Edm           5956-158V-XX        D     20       60         60                                9/30/94*
 F      1   AUI Cable                5956-840Z-XX        D     70       70         70                                9/30/94*
 G      1   CS Daisy Chain           5956-743A-02        D     50       50         50                                9/30/94*
 H      1   Thin Net Segment         NA2020-20           D     25       25         25                                9/30/94*
 I      2   Thin Terminators         SA2034              D     30       60         60                                9/30/94*
 J      2   Thin T Connectors        NA2033              D     10       20         20                                9/30/94*
 K      1   ISX5300v.35 stub cabl    5956-879 ?                80       80         80                                9/30/94*
 L      1   CSU to EDM               5956-858V-XX              20       20         20                                9/30/94*
 N      1   EDM to NTS               5956-146U-XX              50       50         50                                9/30/94*
 B      1   PC to EDM/DDM/SDM        5956-146W           D     50       50        100                                9/30/94*
 O      1   Rtr to DCE (v.35)        WF7220                   215      215        215                                9/30/94*
 G      1   Rtr Consl to Term Svr    WF7526                   105      105        105                                9/30/94*

                                                       Subtotal      2,385      2,435

                                                       Site Total  113,348     96,754
                                                                                        Mo. Maint Install Total
                                                       Total       113,348     96,754     852          3,935
</TABLE> 
<PAGE>
 
CRC - Dial in POP, 76 Modem Site (2 sites)
<TABLE> 
<CAPTION> 
                                                                                                                       Ship
 Item Qty  Description              Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    Date
 <S>  <C>   <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A     4   Excalibur Card Carrier  excs2plus-2ac       D    2,850      11,400       9,690         76             0    9/30/94*
  B     4   System Controller       asetsyscon1a        A    2,400       9,600       8,160         76             0    9/30/94*
  C     4   T-1 CSU                 exaset1csu1         A    2,650      10,600       9,010         80           100    9/30/94*
  D     4   Aset Personality Mod.   Asetpermod          B      700       2,800       2,380         24             0    9/30/94*
  E     1   Aset Mster Control Pnl. Aset1mcp            B      800         800         680          0             0    9/30/94*
  F    38   Dual Modec              dfmodec232          A    2,250      85,500      72,675        684          3800    9/30/94*
  G     1   13Slot Chassis          INX5000TR13C110     A    4,250       4,250       3,613         43           255    9/30/94*
  H     6   NTS Telco               NTSTELCOEK          A    2,485      14,970       2,291        150           900    9/30/94*
  I     1   TCP Featurepak          NTS-TCP-FC          A      295         295       1,785          0             0    9/30/94*
  J     1   Wan Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  K     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  L     1   Ethernet Trans Thin     U3-NT1000                  169         169          95                             9/30/94*
  M     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695       2,695       2,291         18           160    9/30/94*
  N     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*
  O     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  P     2   Rack Configured         C35-01BXXXX         D    2,258       4,516       3,839                             9/30/94*
  Q     2   Outlet Power Strip      AC16AMP24           D      112         224         190                             9/30/94*
  R     2   Fan Assembly            RKFAN               D      162         324         275                             9/30/94*
  S     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  T     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  U     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  V     1   INX Rackmount Shelf     INX Rack MS         D      125         125         106

                                                         Subtotal      154,085     130,972      1,182         5,435
Cables
  A    10   NTS to DCE              5956-139T-XX               160       1,800       1,600                             9/30/94*
  B     1   NTS to DTE              5956-139R-XX               160         160         160                             9/30/94*
  C     4   T-1 CSU to Demarc       5956-840R-XX                50         200         200                             9/30/94*
  D     4   Personality to Edm      5956-743B-XX        D       50         200         200                             9/30/94*
  E     4   T-1 CSU to Edm          5956-158V-XX        D       20          80          80                             9/30/94*
  F     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  G     3   CS Daisy Chain          5956-743A-02        D       50         150         150                             9/30/94*
  H     1   Thin Net Segment        NA2020-20           D       25          25          25                             9/30/94*
  I     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  J     2   Thin T Connectors       NA2033              D       10          20          20                             9/30/94*
  K     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  L     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
  N     1   EDM to NTS              5956-146U-XX                50          50          50                             9/30/94*
  B     1   PC to EDM/DDM/SDM       5956-146W           D       50          50         100                             9/30/94*
  O     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*

                                                         Subtotal        3,085       3,135

                                                         Site Total    157,170     134,107
                                                                                            Mo. Maint  Install Total
                                                         Total         314,340     268,214      2,364        10,870
</TABLE> 
<PAGE>
 
CRC - Dial in POP, 10 Modem Site (1 site)
<TABLE> 
<CAPTION> 
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A     5   Excalibur Card Carrier  excs2plus-2ac       D    2,850      14,250      12,113         95             0    9/30/94*
  B     5   System Controller       asetsyscon1a        A    2,400      12,000      10,200         95             0    9/30/94*
  C     5   T-1 CSU                 exaset1csu1         A    2,650      13,250      11,263        100           100    9/30/94*
  D     5   Aset Personality Mod.   Asetpermod          B      700       3,500       2,975         30             0    9/30/94*
  E     1   Aset Mster Control Pnl. Aset1mcp            B      800         800         680          0             0    9/30/94*
  F    51   Dual Modec              dfmodec232          A    2,250     114,750      97,538        918         5,100    9/30/94*
  G     1   13Slot Chassis          INX5000TR13C110     A    4,250       4,250       3,613         43           255    9/30/94*
  H     7   NTS Telco               NTSTELCOEK          A    2,495      17,465      14,845        175         1,050    9/30/94*
  I     1   TCP Featurepak          NTS-TCP-FC          A      295         295         251          0             0    9/30/94*
  J     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  K     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  L     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  M     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695       2,695       2,291         18           160    9/30/94*
  N     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*
  O     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  P     2   Rack Configured         C35-01BXXXX         D    2,258       4,516       3,839                             9/30/94*
  Q     2   Outlet Power Strip      AC16AMP24           D      112         224         190                             9/30/94*
  R     2   Fan Assembly            RKFAN               D      162         324         275                             9/30/94*
  S     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  T     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  U     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  V     1   INX Rackmount Shelf     INX Rack MS         D      125         125         106                             9/30/94*

                                                         Subtotal      194,430     165,266      1,505        6,885
Cables
  A    13   NTS to DCE              5956-139T-XX               160       2,060       2,080                             9/30/94*
  B     1   NTS to DTE              5956-139R-XX               160         160         160                             9/30/94*
  C     5   T-1 CSU to Demarc       5956-840R-XX                50         250         250                             9/30/94*
  D     5   Personality to Edm      5956-743B-XX        D       50         250         250                             9/30/94*
  E     5   T-1 CSU to Edm          5956-158V-XX        D       20         100         100                             9/30/94*
  F     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  G     4   CS Daisy Chain          5956-743A-02        D       50         200         200                             9/30/94*
  H     1   Thin Net Segment        NA2020-20           D       25          25          25                             9/30/94*
  I     2   Thin Terminators        NA2034              D       30          60          80                             9/30/94*
  J     2   Thin T Connectors       NA2033              D       10          20          20                             9/30/94*
  K     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  L     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
  N     1   EDM to NTS              5956-146U-XX                50          50          50                             9/30/94*
  B     1   PC to EDM/DDM/SDM       5956-146W           D       50          50         100                             9/30/94*
  O     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*

                                                         Subtotal        3,735       3,785

                                                         Site Total    198,165     169,051
                                                                                            Mo. Maint  Install Total
                                                         Total         198,165     169,051      1,505          6,885
</TABLE> 


<PAGE>
 
CRC - Dial in POP, 172 Modem Site (1 site)
<TABLE> 
<CAPTION> 
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             
  A     8   Excalibur Card Carrier  excs2plus-2ac       D    2,850      22,800      19,380        152             0     9/30/94*
  B     8   System Controller       asetsyscon1a        A    2,400      19,200      16,320        152             0     9/30/94*
  C     8   T-1 CSU                 exaset1csu1         A    2,650      21,200      18,020        160           100     9/30/94*
  D     8   Aset Personality Mod.   Asetpermod          B      700       5,600       4,760         48             0     9/30/94*
  E     2   Aset Mster Control Pnl. Aset1mcp            B      800       1,600       1,360          0             0     9/30/94*
  F     86  Dual Modec              dfmodec232          A    2,250     193,500     164,475      1,548         8,600     9/30/94*
  G     1   13Slot Chassis          INX5000TR13C110     A    4,250       4,250       3,613         43           255     9/30/94*
  H     12  NTS Telco               NTSTELCOEK          A    2,495      29,940      25,449        300         1,800     9/30/94*
  I     1   TCP Featurepak          NTS-TCP-FC          A      295         295         251          0             0     9/30/94*
  J     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220     9/30/94*
  K     1   AN Software             WF42021                      0           0           0          0             0     9/30/94*
  L     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                              9/30/94*
  M     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695       2,695       2,291         18           160     9/30/94*
  N     2   EDM                     EDM115                   2,100       4,200       3,570         42           150     9/30/94*
  O     1   3223 Class A            ALM3223                    749         749         637         12           110     9/30/94*
  P     3   Rack Configured         C35-01BXXXX         D    2,258       6,774       5,758                              9/30/94*
  Q     3   Outlet Power Strip      AC16AMP24           D      112         336         286                              9/30/94*
  R     3   Fan Assembly            RKFAN               D      162         486         413                              9/30/94*
  S     1   Fixed Shelf             SELFFIX19           D       73          73          62                              9/30/94*
  T     1   Excal Rackmount         RKMT900             D       75          75          64                              9/30/94*
  U     2   ALM3223 Rackmount       slimline-1          D       75         150         128                              9/30/94*
  V     1   INX Rackmount Shelf     INX Rack MS         D      125         125         106                              9/30/94*
  
                                                         Subtotal      316,962     269,418      2,452        11,135        
Cables
  A    22   NTS to DCE              5956-139T-XX               160       3,520       3,520                              9/30/94*
  B     1   NTS to DTE              5956-139R-XX               160         160         160                              9/30/94*
  C     8   T-1 CSU to Demarc       5956-840R-XX                50         400         400                              9/30/94*
  D     8   Personality to Edm      5956-743B-XX        D       50         400         400                              9/30/94*
  E     8   T-1 CSU to Edm          5956-158V-XX        D       20         160         160                              9/30/94*
  F     1   AUI Cable               5956-840Z-XX        D       70          70          70                              9/30/94*
  G     6   CS Daisy Chain          5956-743A-02        D       50         300         300                              9/30/94*
  H     1   Thin Net Segment        NA2020-20           D       25          25          25                              9/30/94*
  I     2   Thin Terminators        NA2034              D       30          60          60                              9/30/94*
  J     2   Thin T Connectors       NA2033              D       10          20          20                              9/30/94*
  K     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                              9/30/94*
  L     1   CSU to EDM              5956-858V-XX                20          20          20                              9/30/94*
  N     1   EDM to NTS              5956-146U-XX                50          50          50                              9/30/94*
  B     2   PC to EDM/DDM/SDM       5956-146W           D       50         100         100                              9/30/94*
  O     1   Rtr to DCE (v.35)       WF7220                     215         215         215                              9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                              9/30/94*

                                                         Subtotal        5,685       5,685

                                                         Site Total    322,647     275,103
                                                                                            Mo. Maint  Install Total
                                                         Total         322,647     275,103      2,452         11,135
</TABLE> 


<PAGE>
 
CRC - Dial in POP, 226 Modem Site (9 sites)
<TABLE> 
<CAPTION> 
                                                                                                                       
 Item Qty   Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>  <C>   <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A    10   Excalibur Card Carrier  excs2plus-2ac       D    2,850      28,500      24,225        190             0    9/30/94*
  B    10   System Controller       asetsyscon1a        A    2,400      24,000      20,400        190             0    9/30/94*
  C    10   T-1 CSU                 exaset1csu1         A    2,650      26,500      22,525        200           100    9/30/94*
  D    10   Aset Personality Mod.   Asetpermod          B      700       7,000       5,950         60             0    9/30/94*
  E     2   Aset Mster Control Pnl. Aset1mcp            B      800       1,600       1,360          0             0    9/30/94*
  F   113   Dual Modec              dfmodec232          A    2,250     254,250     216,113      2,034        11,300    9/30/94*
  G     1   13Slot Chassis          INX5000TR13C110     A    4,250       4,250       3,613         43           255    9/30/94*
  H     1   3Slot Chassis           INX5000TR3C110      A    2,550       2,550       2,168         26           153    9/30/94*
  I    15   NTS-Telco               NTSTELCOEK          A    2,495      37,425      31,811        375         2,250    9/30/94*
  J     1   TCP Featurepak          NTS-TCP-FC          A      295         295         251          0             0    9/30/94*
  K     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  L     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  M     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  N     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695       2,695       2,291         18           160    9/30/94*
  O     2   EDM                     EDM115                   2,100       4,200       3,570         42           150    9/30/94*
  P     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  Q     3   Rack Configured         C35-01BXXXX         D    2,258       6,774       5,758                             9/30/94*
  R     3   Outlet Power Strip      AC16AMP24           D      112         336         286                             9/30/94*
  S     3   Fan Assembly            RKFAN               D      162         486         413                             9/30/94*
  T     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  U     2   Excal Rackmount         RKMT900             D       75         150         128                             9/30/94*
  V     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  W     2   INX Rackmount Shelf     INX Rack MS         D      125         250         213                             9/30/94*

                                                         Subtotal      405,072     344,311      3,167        14,438
Cables
  A    29   NTS to DCE              5956-139T-XX               160       4,640       4,640                             9/30/94*
  B     1   DCE to DTE              5956-139R-XX               160         160         160                             9/30/94*
  C    10   T-1 CSU to Demarc       5956-840R-XX                50         500         500                             9/30/94*
  D    10   Personality to Edm      5956-743B-XX        D       50         500         500                             9/30/94*
  E    10   T-1 CSU to Edm          5956-158V-XX        D       20         200         200                             9/30/94*
  F     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  G     8   CS Daisy Chain          5956-743A-02        D       50         400         400                             9/30/94*
  H     2   Thin Net Segment        NA2020-20           D       25          50          50                             9/30/94*
  I     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  J     2   Thin T Connectors       NA2033              D       10          20          20                             9/30/94*
  K     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  L     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
  N     1   EDM to NTS              5956-146U-XX                50          50          50                             9/30/94*
  B     2   PC to EDM/DDM/SDM       5956-146W           D       50         100         100                             9/30/94* 
  O     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*

                                                         Subtotal        7,170       7,170

                                                         Site Total    412,242     351,481
                                                                                            Mo. Maint  Install Total
                                                         Total         412,242     351,481      3,167        14,438
</TABLE> 


<PAGE>
 
CRC - BBS POP, 12 Port Site (16 sites)
<TABLE> 
<CAPTION> 
                                                                                                                       
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  B     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  C     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   A    2,695       2,695       2,291         18           160    9/30/94*
  D     1   Terminal Server         ILNTS-16c-110       A    2,995       2,995       2,548         30           180    9/30/94*
  E     1   TCP Featurepak          DKNTSTCPFP          A      495         495         421          0             0    9/30/94*
  F     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  G     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  H     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*

                                                           Subtotal     11,948      10,156         91           570    9/30/94*
                                           
Cables
  A    12   DTE Cable               5956-178N-XX                50         600          50                             9/30/94*
  B     1   DTE Cable               5956-178A-XX                50          50          50                             9/30/94*
  C     1   DCE Cable               5956-178B-XX                50          50          50                             9/30/94*
  D     1   DCE Cable               5956-17BC-XX                50          50          50                             9/30/94*
  D     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  E     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*
  F     1   Thin Net Segment        NA2020-20           D       25          25          25                             9/30/94*
  G     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  H     2   Thin T Connectors       NA2033              D       10          20          20                             9/30/94*
  I     1   Rack Configured         C35-01BXXXX         D    2,258       2,258       1,919                             9/30/94*
  J     1   Outlet Power Strip      AC16AMP24           D      112         112          95                             9/30/94*
  K     1   Fan Assembly            RKFAN               D      162         162         138                             9/30/94*
  L     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  M     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  N     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  O     1   IL Rackmount            IL Rack MB          D       35          35          30                             9/30/94*
  P     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  Q     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
   
                                                       Subtotal          4,135       3,117

                                                       Site Total       16,083      13,273
                                                                                            Mo. Maint  Install Total
                                                       Total           241,245     185,822      1,274          9,360
</TABLE> 
<PAGE>
 
CRC - BBS POP, 32 Port Site (14 sites)
<TABLE> 
<CAPTION> 
                                                                                                                       
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  B     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  C     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   A    2,695       2,695       2,291         18           160    9/30/94*
  D     2   Terminal Server         ILNTS-16c-110       A    2,995       5,990       5,092         60           360    9/30/94*
  E     1   TCP Featurepak          DKNTSTCPFP          A      495         495         421          0             0    9/30/94*
  F     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  G     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  H     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*
                                                           Subtotal     14,943      12,702        121           850    9/30/94*
                                           
Cables
  A    32   DTE Cable               5956-178N-XX                50       1,600       1,600                             9/30/94*
  B     1   DTE Cable               5956-178A-XX                50          50          50                             9/30/94*
  C     1   DCE Cable               5956-178B-XX                50          50          50                             9/30/94*
  D     1   DCE Cable               5956-17BC-XX                50          50          50                             9/30/94*
  E     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  F     1   Rtr to DCE (v.35)       WF7220                     215         215         215                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*
  F     3   Thin Net Segment        NA2020-20           D       25          50          50                             9/30/94*
  G     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  H     2   Thin T Connectors       NA2033              D       10          30          30                             9/30/94*
  I     1   Rack Configured         C35-01BXXXX         D    2,258       2,258       1,919                             9/30/94*
  J     1   Outlet Power Strip      AC16AMP24           D      112         112          95                             9/30/94*
  K     1   Fan Assembly            RKFAN               D      162         162         138                             9/30/94*
  L     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  M     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  N     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  O     1   IL Rackmount            IL Rack MB          D       35          35          30                             9/30/94*
  P     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  Q     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
                                                       Subtotal          5,170       4,752

                                                       Site Total       20,113      17,454
                                                                                            Mo. Maint  Install Total
                                                       Total           281,582     191,994    191,994          9,350
</TABLE> 

<PAGE>
CRC - BBS POP, 48 Port Site (1 sites)
<TABLE> 
<CAPTION> 
                                                                                                                       
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A     1   WAN Router              WF20002                  2,745       2,745       2,333         31           220    9/30/94*
  B     1   AN Software             WF42021                      0           0           0          0             0    9/30/94*
  C     1   ISX 5300 Single DS1     ISX500SA-CMS-CS01   A    2,695       2,695       2,291         18           160    9/30/94*
  D     3   Terminal Server         ILNTS-16c-110       A    2,995       8,985       7,637         90           540    9/30/94*
  E     1   TCP Featurepak          DKNTSTCPFP          A      495         495         421          0             0    9/30/94*
  F     1   Ethernet Trans Thin     U3-NT1000                  169         169         144                             9/30/94*
  G     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  H     1   EDM                     EDM115                   2,100       2,100       1,785         21           150    9/30/94*

                                                         Subtotal       17,938      15,247        151         1,030    9/30/94*
Cables
  A    48   DTE Cable               5956-178N-XX                50       2,400       2,400                             9/30/94*
  B     1   DTE Cable               5956-178A-XX                50          50          50                             9/30/94*
  C     1   DCE Cable               5956-178B-XX                50          50          50                             9/30/94*
  D     1   DCE Cable               5956-178C-XX                50          50          50                             9/30/94*
  E     1   AUI Cable               5956-840Z-XX        D       70          70          70                             9/30/94*
  F     1   Rtr to DCE (v.35)       WF7220                     215         215         105                             9/30/94*
  G     1   Rtr Consl to Term Svr   WF7526                     105         105         105                             9/30/94*
  F     3   Thin Net Segment        NA2020-20           D       25          75          75                             9/30/94*
  G     2   Thin Terminators        NA2034              D       30          60          60                             9/30/94*
  H     4   Thin T Connectors       NA2033              D       10          40          40                             9/30/94*
  I     1   Rack Configured         C35-01BXXXX         D    2,258       2,258       1,919                             9/30/94*     
  J     1   Outlet Power Strip      AC16AMP24           D      112         112          95                             9/30/94*
  K     1   Fan Assembly            RKFAN               D      162         162         138                             9/30/94*
  L     1   Fixed Shelf             SELFFIX19           D       73          73          62                             9/30/94*
  M     1   Excal Rackmount         RKMT900             D       75          75          64                             9/30/94*
  N     1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  O     1   IL Rackmount            IL Rack MB          D       35          35          30                             9/30/94*
  P     1   ISX5300 v.35 stub cabl  5956-879 ?                  80          80          80                             9/30/94*
  Q     1   CSU to EDM              5956-858V-XX                20          20          20                             9/30/94*
  
                                                         Subtotal        6,005       5,477

                                                         Site Total     23,943      20,724
                                                                                            Mo. Maint  Install Total
                                                         Total          23,843      62,172        453         3,090
</TABLE> 


<PAGE>

CRC - Data Center
<TABLE> 
<CAPTION> 
                                                                                                                       Ship
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    Date
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A     7   RM1690                  RM1690M2AA          D    2,195      15,365      13,060         70         1,750    9/30/94*
  B   100   RM3268                  RMD3268CS2          A    1,695     169,500     144,875      1,200        12,000    9/30/94*
  C     9   7000-I Channel Bank      T000P10             C    4,588      41,292      35,098        306         2,448    9/30/94*
  D     9   Power Conv. AC to 48    T66900              D      303       2,727       2,318         18           162    9/30/94*
  E    27   Ring Generator          T669100             D      303       8,181       6,954         54           486    9/30/94*
  F     9   PS/Ring Gen Shelf       T310010             D      330       2,970       2,525         18           162    9/30/94*
  G   200   2W FXS/FXSON            T244340             C      440      68,000      74,800        600         5,200    9/30/94*
  H    16   Blank Card              T249900             D       28         448         381                       32    9/30/94*
  I     1   ICSU                    D347400             C    4,095       4,095       3,481         31           246    9/30/94*
  J     9   LC02B CSU Card          D439900             C    2,462      22,158      18,834        162         1,332    9/30/94*
  K     0   Excalibur Card Carrier  excs2plus-2ac       D    2,850           0           0          0             0    9/30/94*
  L     0   System Controller       asetsyscon1a        A    2,400           0           0          0             0    9/30/94*
  M     0   T-1 CSU                 exaset1csu1         A    2,650           0           0          0           100    9/30/94*
  N     0   Aset Personality Mod.   Asetpermod          B      700           0           0          0             0    9/30/94*
  O     0   Aset Mster Control Pnl. Aset1mcp            B      800           0           0          0             0    9/30/94*
  P     0   Dual Modec              dfmodec232          A    2,250           0           0          0             0    9/30/94*
  Q     2   13 Slot Chassis         INX5000TR13C110     A    2,550       5,100       4,335         86           510    9/30/94*
  R    13   NTS Telco               NTSTELCOEK          A    2,495      32,435      27,570        325         1,950    9/30/94*
  S     2   TCP Featurepak          NTS-TCP-FC          A      295         590         502          0             0    9/30/94*
  T     2   Ethernet trans Thin     U3-NT1000                  169         338         287                             9/30/94*
  U     5   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695      13,475      11,454         90           160    9/30/94*
  V     5   EDM                     EDM115                   2,100      10,500       8,925        105           150    9/30/94*
  W     1   3223 Class A            ALM3223                    749         749         637         12           110    9/30/94*
  X     3   Rack Configured         C25-01BXXXX         D    2,258       6,774       5,758                             9/30/94*
  Y     3   Outlet Power Strip      AC16AMP24           D      112         336         286                             9/30/94*
  Z     3   Fan Assembly            RKFAN               D      162         486         413                             9/30/94*
  A1    3   Fixed Shelf             SELFFIX19           D       73         219         186                             9/30/94*
  B1    4   Excal Rackmount         RKMT900             D       75         300         255                             9/30/94*
  C1    1   ALM3223 Rackmount       slimline-1          D       75          75          64                             9/30/94*
  D1    2   INX Rackmount Shelf     INX Rack MS         D      125         250         213                             9/30/94*
  E1    2   Backbone Link Node      WF71000             A   18,150      36,300      30,855        410         2,904    9/30/94*
  F1    2   BN Flash Media 7.70     WF75050             -      550       1,100         935         12            86    9/30/94*
  G1    2   Frame Relay Software    WF42014             -        0           0           0                             9/30/94*
  H1    2   FRE2 Dual Enet/Sync.    WF74009-16              15,400      30,800      26,180        398         2,816    9/30/94*
  I1    2   FRE2 Quad Sync          WF74000-16              15,400      30,800      26,180        348         2,464    9/30/94*
  J1    2   Multi mode FDDI ILI     WF74012-16              21,450      42,900      36,465        484         3,432    9/30/94*
  K1    1   Site Manager DOS        WF40034                    110         110          94          1             9    9/30/94*
  L1    2   BLN SRM-F               WF75010                  1,650       3,300       2,805         38           264    9/30/94*

                                                         Subtotal      571,673     485,922
Cables
  A    25   NTS to DCE              5956-139T-XX               160       4,000       4,000                             9/30/94*
  B     9   T-1 CSU to Demarc       5956-840R-XX                50         450         450                             9/30/94*
  C     9   Personality to Edm Ca   5956-743B-XX        D       50         450         450                             9/30/94*
  D     9   T-1 CSU to Edm Cable    5956-158V-XX        D       20         180         180                             9/30/94*
  E     2   AUI Cable               PN8060              D       70         140         140                             9/30/94*
  F     0   Daisy Chain Cable for m 5956-743A-02        D       50           0           0                             9/30/94*
  G     4   Thin Net Segment        NA2020-20           D       25         100         100                             9/30/94*
  H     4   Thin Terminators        NA2034              D       30         120         120                             9/30/94*
  I     4   Thin T Connectors       NA2033              D       10          40          40                             9/30/94*
  J     5   Rtr to DCE (v.35)       WF7255              B       94         470         470                             9/30/94*
  K     4   CSU to EDM              5956-858V-XX        B       20          80          80                             9/30/94*
  L     2   Rtr Console to NTS      5956-178N-XX        B       50         100         100                             9/30/94*
  M     5   ISX5300 v.35 stub cabl  5956-879 ?                  80         400         400                             9/30/94*
  N     2   FDDI Sngl Attach FSD    WF7135                     495         990         990                             9/30/94*
  W    28   1690 to Dial            5956-139F                  160       4,480       4,480                             9/30/94*
  X     9   Super Mod 24            TRW24                       81         729         729                             9/30/94*
  Y     9   7000 to ICSU            5956-840P                   50         450         450                             9/30/94*
  Z     9   7000 CSU to CTRL        5956-864M                   50         450         450                             9/30/94*
  A1    9   7000 CTRL to DCE        PD20338                     50         450         450                             9/30/94*
  B1    9   ICSU to Demarc          5956-840R                   50         450         450                             9/30/94*
  C1    9   Dual Line Cable         5956-130F                  100         900         900                             9/30/94*

                                                         Subtotal        7,520      15,429
                                                                                            Mo. Maint  Install Total
                                                         Site Total    579,193     501,351      4,768        38,775
</TABLE> 


<PAGE>
 
CRC - Network Management System

<TABLE> 
<CAPTION> 
                                                                                                                       
 Item  Qty  Description             Part Number        Cat  List     Ext. Price  CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C>        <C>        <C>             <C> 
  A     3   Ext. Drag Mix           EDM115              A    2,100       6,300       5,355         63           450    9/30/94*
  C     1   CMS 400 Basic Kernel    CMSBASIC            A    2,000       2,000       1,700         20           150    9/30/94*
  D     1   ENAR Acess Manager      CMS400ENAR-24       A    5,000       5,000       4,250         30           150    9/30/94*
  E     1   LAN Internet Mgr 2000   CMSLIM2             A    5,000       5,000       4,250         50           300    9/30/94*
  F     1   Station Dist. Mux       SDM220              A    2,500       2,500       2,125         21           150    9/30/94*
  G     1   Hub PC                  DPC-CMS400               4,600       4,600       3,910         18           150    9/30/94*
  H     1   Monitor                 DELL-14CM                  560         560         476                             9/30/94*
  I     1   Ethernet Card for CMS   LPAETH                     490         490         417                             9/30/94*
  J     1   Printer                 PRT-KXP2124                485         485       1,573                             9/30/94*  
  K     1   Artic Kit for DPC-CMS   Artic-ISA                1,850       1,850       1,573                             9/30/94*
  L     1   CMS 6000 SW HPOPE       Quickstart1         D   28,875      28,875      24,544        200                  9/30/94*
  M     1   CMS Op. License 2-4     SWTK2               C    6,000       6,000       5,100         75                  9/30/94*
  N     1   CMS 6000 Trouble Tkt    SWTV1B              C    2,000       2,000       1,700         25                  9/30/94*
  O     1   CMS 6000 Perform An.    SWTV4               C    3,500       3,500       2,975         44                  9/30/94*
  P     1   CMS6000 Animated Gl.    SWTV3               C      750         750         638          8                  9/30/94*
  Q     1   CMS400 Agent Mgmt       SWTC1               C    4,000       4,000       3,400         50                  9/30/94*
  R     1   LAN SNMP AMM            SWTC7               C    5,000       5,000       4,250         63                  9/30/94*
  S     1   ICSU Manager AM         ICSUAMM             C    5,900       5,900       5,015         74                  9/30/94*
  T     1   CMS400 Sun/Motif TE     400/MOTIF           C    1,200       1,200       1,020         15                  9/30/94*
  U     1   Ethernet Trans Thin     U3-NT1000                  169         169         287                             9/30/94*

                                                          Subtotal      86,179      73,252

Cables
  A     8   EDM to DDM              5956-146Y           D       50         400         400                             9/30/94*   
  B     2   PC to EDM/DDM/SDM       5956-146W           D       50         100         100                             9/30/94*
  C     1   Network Mgmt Cables                         D      927         927         927                             9/30/94*
  D     2   CMS6000/Sun to SDM      5956-165J           D      150         300         300                             9/30/94*
  E     1   AUI Cable               PN8060              D       70          70         140                             9/30/94*
      
                                                     Total               1,797       1,797

                                                              Total     87,976      75,049       757          1,350
</TABLE> 
                                                         
<PAGE>
 
<TABLE> 
<CAPTION> 

                                                   List               CRC Price         Mo. Maint       Install
<S>                                               <C>                 <C>               <C>             <C>
Summary of Racal Datacomm Proposal
     
     Dial-In Points of Presence (97)              5,712,280                               41,971        196,152

     BBS Points of Presence (30)                    546,770                                3,058         21,820

     Data Center (Dial-in Access and Routers)       579,193                                4,768         38,775

     Network Management                              87,976                                  757          1,350

                                                                                        Mo. Maint Total
                                                                                          50,554
                                                                                       Ann. Main        Install Total
                                  Project Total   6,926,219                          0   606,648        258,097
</TABLE> 
<PAGE>
 
CRC - Equipment Summary
<TABLE> 
<CAPTION> 
 Item Qty   Description             Part Number        Cat  List     Ext. Price      CRC Price  Ext Maint  Ext. Install    
 <S>   <C>  <C>                     <C>                <C>  <C>      <C>         <C> <C>        <C>        <C>             <C> 
  A   137   Excalibur Card Carrier  excs2plus-2ac       D    2,850     390,450   10%   351,405      2,603             0    9/30/94*
  B   137   System Controller       asetsyscon1a        A    2,400     328,800   20%   263,640      2,603             0    9/30/94*
  C   137   T-1 CSU                 exaset1csu1         A    2,650     363,050   20%   290,440      2,740           100    9/30/94*
  D   137   Aset Personality Mod.   Asetpermod          B      700      95,900   15%    81,515        822             0    9/30/94*
  E    99   Aset Mster Control Pnl. Aset1mcp            B      800      79,200   15%    67,320          0             0    9/30/94*
  F  1114   Dual Modec              dfmodec232          A    2,250   2,506,500   20% 2,005,200     20,052       111,400    9/30/94*
  G   154   Terminal Server         ILNTS-16c-110       A    2,995     461,230   20%   368,984      4,620        27,720    9/30/94*
  G    19   3Slot Chassis           INX5000TR3C110      A    2,550      48,450   20%    38,760        494         2,907    9/30/94*
  G     8   13Slot Chassis          INX5000TR13C110     A    4,250      34,000   20%    27,200         43         2,040    9/30/94*
  H   103   NTS Telco               NTSTELCOEK          A    2,495     256,985   20%   205,588      2,575        15,450    9/30/94*
  H   109   TCP Featurepak          DKNTSTCPFC          A      295      32,155   20%    25,724          0             0    9/30/94*
  H    20   TCP Featurepak          NTS-TCP-FC          A      295       5,900   20%     4,720          0             0    9/30/94*
  I   127   WAN Router              WF20002             B    2,745     348,615   15%   296,323      3,937        27,940    9/30/94*
  J   127   AN Software             WF42021             B        0           0   15%         0          0             0    9/30/94*
  K   129   Ethernet Trans Thin     U3-NT1000           C      169      21,801   20%    17,441                             9/30/94*
  L   132   ISX 5300 Single DS1     ISX500SA-CMS-CS01   B    2,695     355,740   15%   302,379      2,376        21,120    9/30/94*
  M   135   EDM                     EDM115              A    2,100     283,500   30%   198,450      2,835        20,250    9/30/94*
  N   128   3223 Class A            ALM3223             A      749      95,872   30%    67,110      1,536        14,080    9/30/94*
  O   137   Rack Configured         C35-01BXXXX         D    2,258     309,346   10%   278,411                             9/30/94*
  P   137   Outlet Power Strip      AC16AMP24           D      112      15,344   10%    13,810                             9/30/94*
  Q   137   Fan Assembly            RKFAN               D      162      22,194   10%    19,975                             9/30/94*
  R   130   Fixed Shelf             SELFFIX19           D       73       9,490   10%     8,541                             9/30/94*
  S   132   Excal Rackmount         RKMT900             D       75       9,900    0%     9,900                             9/30/94*
  T   129   ALM3223 Rackmount       slimline-1          D       75       9,675    0%     9,675                             9/30/94*
  U   138   IL Rackmount            IL Rack MB          D       35       4,830    0%     4,830                             9/30/94*
  V    21   INX Rackmount Shelf     INX Rack MS         D      125       2,625    0%     2,625                             9/30/94*
  W     2   Backbone Link Node      WF71000             B   18,150      36,300   15%    30,855        410         2,904    9/30/94*
  X     2   BN Flash Media 7.70     WF75050             B      550       1,100   15%       935         12            88    9/30/94*
  Y     2   Frame Relay Software    WF42014             B        0           0               0                             9/30/94*
  Z     2   FRE2 Dual Enet/Sync.    WF74009-16          B   15,400      30,800   15%    26,180        398         2,816    9/30/94*
  A1    2   FRE2 Quad Sync          WF74000-16          B   15,400      30,800   15%    26,180        348         2,464    9/30/94*
  B1    2   Multi mode FDDI ILI     WF74012-16          B   21,450      42,900   15%    36,465        484         3,432    9/30/94*
  C1    1   Site Manager DOS        WF40034             B      110         110   15%        94          1             9    9/30/94*
  D1    2   BLN SRM-F               WF75010             B    1,650       3,300   15%     2,805         38           264    9/30/94*
  E1    1   CMS 400 Basic Kennel    CMSBASIC            C    2,000       2,000    5%     1,900         20           150    9/30/94*
  F1    1   Enar Access Manager     CMS400ENAR-24       C    5,000       5,000    5%     4,750         30           150    9/30/94*
  G1    1   LAN Internet Mgr 2000   CMSLIM2             C    5,000       5,000    5%     4,750         50           300    9/30/94*
  H1    1   Station Dist. Mux       SDM220              A    2,500       2,500   20%     2,000         21           150    9/30/94*
  I1    1   Hub PC                  DPC-CMS400          A    4,600       4,600   10%     4,140         18           150    9/30/94*
  J1    1   Monitor                 DELL-14CM           A      560         560   10%       504                             9/30/94*
  K1    1   Ethernet Card for CMS   LPAETH              A      490         490   10%       411                             9/30/94*
  L1    7   RM1690                  RM1690M2AA          D    2,195      15,365    0%    15,365         70         1,750    9/30/94*
  M1  100   RM3268                  RMD3268CS2          C    1,695     169,500    5%   161,025      1,200        12,000    9/30/94*
  N1    9   7000-I Channel Bank     T000P10             C    4,588      41,292    5%    39,227        306         2,448    9/30/94*
  O1    9   Power conv. AC to 48    T66900              D      303       2,727    0%     2,727         18           162    9/30/94*
  P1   27   Ring Generator          T669100             D      303       8,181    0%     8,181         54           486    9/30/94*
  Q1    9   PS/Ring Gen Shelf       T310010             D      330       2,970    0%     2,970         18           162    9/30/94*
  R1  200   2W FXS/FXSDN            T244340             C      440      88,000    5%    83,600        600         5,200    9/30/94*
  S1   16   Blank Card              T249900             D       28         448    0%       448                       32    9/30/94*
  T1    1   ICSU                    D347400             C    4,095       4,095    5%     3,890         31           246    9/30/94*
  U1    9   LC02B CSU Card          D439900             C    2,462      22,158    5%    21,050        162         1,332    9/30/94*
  V1    1   CMS 6000 SW HPOPE       Quickstart1         D   26,675      28,875    0%    28,875        200                  9/30/94*
  W1    1   CMS Op. License 2-4     SWTK2               C    6,000       6,000    5%     5,700         75                  9/30/94*
  X1    1   CMS 6000 Trouble Tkt    SWTV1B              C    2,000       2,000    5%     1,900         25                  9/30/94*
  Y1    1   CMS 6000 Perform An.    SWTV4               C    3,500       3,500    5%     3,325         44                  9/30/94*
  Z1    1   CMS6000 Animated Gl.    SWTV3               C      750         750    5%       713          9                  9/30/94*
  A2    1   CMS400 Agent Mgmt       SWTC1               C    4,000       4,000    5%     3,800         50                  9/30/94*
  B2    1   LAN SNMP AMM            SWTC7               C    5,000       5,000    5%     4,750         63                  9/30/94*
  C2    1   ICSU Manager AM         ICSUAMM             C    5,900       5,900    5%     5,605         74                  9/30/94*
  D2    1   CMS400 Sun/Motif TE     400/MOTIF           C    1,200       1,200    5%     1,140         15                  9/30/94*
 
                                                         Subtotal    6,668,973       5,495,655     52,080       255,884
                                                     Old Subtotal    6,520,673       5,582,579     42,185       166,325
</TABLE> 
<PAGE>
 
<TABLE> 
<CAPTION> 

Cables
<S>   <C>   <C>                         <C>               <C>     <C>   <C>       <C>      <C>                 <C> 
A      18    NTS to DTE                  5956-139R-XX      D      160    2,880    30%       2,016              9/30/94* 
B     180    NTS to DCE                  5956-13ST-XX      D      160   28,800    30%      20,160              9/30/94*
C      18    EDM to DDM                  5956-146U-XX      D       50      900    30%         630              9/30/94*
D       8    EDM to DDM                  5956-146Y         D       50      400    30%         280              9/30/94*
E      22    PC to EDM/DDM/SDM           5956-146W         D       50    1,100    30%         770              9/30/94*
F     146    T-1 CSU to Edm              5956-158V-XX      D       20    2,920    30%       2,044              9/30/94*
G     127    EDM to NTS                  5956-178A-XX      D       50    6,350    30%       4,445              9/30/94* 
H    1211    NTS to DCE                  5956-178B-XX      D       50   60,550    30%      42,385              9/30/94*    
H     109    NTS to DTE                  5956-178C-XX      D       50    5,450    30%       3,815              9/30/94*
I     513    Rtr Console to NTS          5956-178N-XX      D       50   25,650    30%      17,955              9/30/94*
J      37    CS Daisy Chain              5956-743A-02      D       50    1,850    30%       1,295              9/30/94*
K     698    Personality to Edm          5956-743B-XX      D       50   34,900    30%      24,430              9/30/94*
L     146    T-1 CSU to Demarc           5956-840R-XX      D       50    7,300    30%       5,110              9/30/94*
M     127    AUI Cable                   5956-840Z-XX      D       70    8,890    30%       6,223              9/30/94*
N     131    CSU to EDM                  5956-858V-XX      D       20    2,620    30%       1,834              9/30/94*
O     132    ISX5300 v.35 stub cabl      5956-879 ?        D       80   10,560    30%       7,392              9/30/94*  
P     177    Thin Net Segment            NA202020          D       25    4,425    30%       3,098              9/30/94*
Q     258    Thin Terminators            NA2034            D       30    7,740    30%       5,416              9/30/94*
R     290    Thin T Connectors           NA2033            D       10    2,900    30%       2,030              9/30/94*
S     127    Rtr to DCE (v.35)           WF7220            D      215   27,305    30%      19,114              9/30/94*
S     129    Rtr Consl to Term Svr       WF7526            D      105   13,545    30%       9,482              9/30/94*
T       4    Rtr to DCE (v.35)           WF7255            D       94      376    30%         263              9/30/94* 
U       3    AUI Cable                   PN8060            D       70      210    30%         147              9/30/94*
V       2    FDDI Sngl Attach FSD        WF7135            D      495      990    30%         693              9/30/94*
W      28    1690 to Dial                5956-139F                160    4,480    30%       3,136              9/30/94*
X       9    Super Mod 24                TRW24                     81      729    30%         510              9/30/94* 
Y       9    7000 to ICSU                5956-840P                 50      450    30%         315              9/30/94*
Z       9    7000 CSU to CTRL            5956-864M                 50      450    30%         315              9/30/94*
A1      9    7000 CTRL to DCE            PD20338                   50      450    30%         315              9/30/94*
B1      9    ICSU to Demarc              5956-840R                 50      450    30%         315              9/30/94*
C1      9    Dual Line Cable             5956-130F                100      900    30%         630              9/30/94*
D1      2    CMS6000/Sun to SDM          5956-165J         D      150      300    30%         300              9/30/94* 
                                                              Total                       186,864
                                                  
                                              Professional Services    100,000            100,000 mo maint install

             0.285714286                                Grand Total  6,855,837          5,782,519    42,185  166,325
                                                48 Month Lease Rate    0.02805            162,200              4,665
</TABLE> 

* A mutually agreed upon shipping schedule shall be determined in the two weeks
following the contract signing to make adjustments to this ship date. All
equipment shall ship by 8/3/95.
<PAGE>
 
The Racal Corporation
Law Department
1801 N. Harrison Parkway
Sunrise, Florida 33323-2899
Telephone
Telecopier
                                           Please reply to:
                                           PO Box 407044
                                           Ft. Lauderdale, FL 33340-7044
                                           Direct Dial:

March 30, 1995


Mr. Don Schutt, Chief Operating Officer
Concentric Research Corporation
400 Forty First Street
Bay City, MI 48708

Dear Don:

I am writing to confirm the agreements that we reached at our meeting today
respecting certain matters involving the business relationships between Racal-
Datacom, Inc. ("RDI") and Concentric Research Corporation ("CRC") as set forth
below.

1.  With respect to the Master Lease Agreement No. CON01C, dated August 4, 1994,
    between RDI and CRC (the "Agreement"), we agreed that (a) the Commencement
    Date as defined in section iv. of the Agreement shall be March 31, 1995. The
    Equipment (as that term is defined in the Agreement) has been Deployed at
    the sites set forth in Exhibit A which is attached to this letter.

2.  With respect to initial monthly billing and payments, we have agreed as
    follows:

     (a) The monthly billing as of this date based upon Equipment which has been
         ordered pursuant to an RDI sales order in not less than $205,842.50 per
         month and may equal $210,714.69 per month for the term stated on each
         order. RDI believes that the monthly billing amount equals $210,714.69.
         RDI shall provide CRC with documentation to support its contention of
         the current monthly billing amount.


<PAGE>
 
     (b) Payments for the items set forth in 2(a) for the months of April, May
         and June, 1995 shall be deferred until and shall commence on July 15,
         1995. The payments due for April, May and June, 1995 shall be amortized
         over the six month period commencing July 15, 1995 through December 15,
         1995 (the "Deferred Payment period"). The resulting monthly payment
         will be:

             $205,842.50 (or, $210,714.69 based upon RDI's substantiation) 
      plus     70,238.23 (1/6 of the April, May and June obligation)
             -----------
     Total   $276,080.73

     The total does not include any other RDI charges for additional equipment
     or services ordered after this date or charges provided for in any of the
     agreements existing between CRC and RDI on the date hereof.

3.   Certain outstanding nor invoices to CRC are set forth below. They will be
     paid as follows:

     (a) RDI invoice number 796676 for professional services in the amount of 
         $150,000.00. This invoice shall be paid prior to April 15, 1995.

     (b) RDI Invoice number 796677 in the amount of $94,776.72. RDI shall
         provide CRC with the documentation in its possession and cooperate with
         CRC in efforts to secure the credit from AT&T to CRC which was
         previously negotiated among CRC, RDI and AT&T for the invoiced amount.
         CRC shall pay RD: the invoiced amount immediately upon CRC's receipt of
         the credit in this amount from AT&T.

     (c) RDI Invoice number INV5435 in the amount of $40,599.81 for actual
         freight charges for Equipment shipped pursuant to the Agreement. RD:
         shall provide CRC with such backup material for the freight charges
         incurred as reasonably requested by CRC. This invoice shall be paid
         prior to April 15, 1995.

     We have agreed that the invoices set forth in items 3(a) and 3(c) shall
     accrue interest at a rate of 10% commencing on March 31, 1995 and
     continuing until the invoices have been paid, provided, however, if CRC has
     paid the aforementioned invoices on or prior to April 15, 1995, RDI shall
     waive the accrued interest.

4.   The Sun Bank loan will be repaid by CRC in accordance with the terms set
     forth in the Reimbursement Agreement between nor and CRC dated as of
     February 15, 1995 or prior to April 15, 1995, whichever occurs earlier.

<PAGE>
 
5.   CRC and RDI are parties to a Remote Network Operations Agreement number
     CON03C between CRC and RDI, dated October 14, 1994 (the "Net Ops
     Agreement") which provides for monthly payments from CRC to RDI in the
     amount of [*] for a period of forty-eight (48) months (extended
     value [*]), CRC has expressed a desire to secure services in lieu of
     those provided for in the Net Ops Agreement. RDI has proposed a Network
     services Transition Program. CRC and RDI agree to negotiate in good faith
     to attempt to reach an agreement respecting the provision of a Network
     Services program by RDI which would supersede the Net Ops Agreement.

6.   RDI shall prepare and present to CRC and Critical Technologies Inc.
     ("Critical") proposed leases for space in connection with the eight RDI
     locations which are currently P.O.P. sites for the deployed Equipment. RDI,
     CRC and Critical shall negotiate in good faith towards a lease for the
     P.O.P. site.

7.   Prior to assuming its seat on CRC'S Board of Directors, RDI will exercise
     its warrants on 100,000 shares of CRC'S common stock at one dollar per
     share. We have further agreed that the exercise price can, at RDI's option,
     be payable by the forgiveness of debt, in the form of the issuance of a
     credit to CRC.

Other than item 2, respecting the deferral of CRC's payment obligations for the
months of April, May and June, 1995, nothing contained in this letter is
intended to or shall amend, alter, cancel, or extinguish any rights or
obligations of CRC or RDI under any existing agreements between us.

If the foregoing is acceptable to CRC, please signify by signing in the space
provided below.


Joseph E. Carpenter, Jr.
General Counsel and
Senior Vice President, Administration


Accepted on behalf of Concentric Research Corporation this 30th day of 
March, 1995.
Concentric Research Corporation

By: Don Schutt
as its Chief Operating Officer

- -----------------------

     [*]Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.
<PAGE>
 
                                                                     Exhibit A

[*]

- ---------------------
     [*]Certain information in this exhibit has been omitted and filed
separately with the Securities and Exchange Commission.  A total of 4 pages
containing such information has been omitted from this exhibit.  Confidential
treatment has been requested with respect to the omitted portions.

<PAGE>
 
                                                                 EXHIBIT 10.23

                        LEASE AGREEMENT NUMBER CONO4C


     This lease agreement ("Agreement") is entered into this 26th day of June,
1996 by and between Concentric Network Corporation, a Florida corporation
(hereinafter referred to as "Lessee") having its principal place of business at
10590 North Tantau Avenue, Cupertino, California 95014 and Racal-Datacom, Inc.,
a Delaware corporation, (hereinafter referred to as "Lessor" or "R-D"), having
its principal place of business located at 1601 North Harrison Parkway, Sunrise,
Florida 33323-2899, organizations duly authorized by law.

                                WITNESSETH THAT

     WHEREAS, Lessor is the manufacturer of data communication products which
are composed of hardware (hereinafter referred to as "Equipment"), and software
which is defined as a set of processor instructions that can be ported into a
processor and executed to provide a defined functionality (hereinafter referred
to as "Software"); and,

     WHEREAS, Lessee is desirous of leasing such Equipment or Software from
Lessor for use with Lessee's communications network; and,

     WHEREAS, both parties are desirous of establishing the terms and conditions
which shall govern all orders issued pursuant to this Agreement.

     NOW THEREFORE, in consideration of the covenants, premises and mutual
agreements contained herein, the parties do hereby agree as follows:

I.   PURPOSE
     -------

     The purpose of this Agreement is to set forth the terms and conditions
pursuant to which Lessee may submit orders (as defined in Article III) to
Lessor.  All Orders must be accepted by Lessor at its headquarters, Sunrise,
Florida.

II.  TERM OF AGREEMENT
     -----------------

     This Agreement shall commence upon the date first written above and shall
continue for a term of twelve (12) months thereafter.  This Agreement shall
govern all Orders placed hereunder provided such Orders are received by Lessor
within twelve (12) months and the Equipment and Software ordered is installed
within fourteen (14) months, both of said periods beginning upon the date of
commencement of this Agreement.  Thereafter, this Agreement shall automatically
renew itself in twelve (12) month increments unless either party notifies the
other of its decision to terminate this Agreement by providing the other party
sixty (60) days written notice prior to the expiration of the period then in
effect.
<PAGE>
 
     Notwithstanding that this Agreement may terminate prior to the expiration
of an individual Order's term, it is expressly agreed that any Order issued
pursuant to this Agreement shall continue to be in full force and effect and
continue to be governed by the terms hereof until the expiration of such Order's
stated minimum term.

III. ORDERING PROCEDURE
     ------------------

     Lessee shall issue Orders (hereinafter defined as "Orders") to Lessor on
Lessor's order form or Lessee's order form.  At a minimum, such Orders shall
include the following information:

     1.  Description of Equipment to be leased and Software to be licensed.

     2.  Quantity of each item of Equipment or Software.

     3.  Monthly lease rate, lease term and license fee for each item.

     4.  Unit installation price for each item (if applicable).

     5.  Unit purchase price for each item.

     6.  Requested delivery date.

     7.  Shipping location and Lessee prime contact at shipping location.

     8.  Billing address and billing contact.

     9.  Required Lessor services such as standard handling, installation,
         maintenance, training and engineering costs (if applicable), and their
         respective charges.

     Lessor will acknowledge acceptance or rejection of Orders within fifteen
(15) days after receipt of the Order at Lessor's principal place of business,
Sunrise, Florida.  Once accepted, the Order is noncancelable.  If Lessor
proposes a delivery schedule different from the schedule requested by Lessee,
Lessee must notify Lessor of its rejection of such alternate delivery schedule
within fifteen (15) days after mailing of such notification by Lessor, or the
Lessor proposed shipping date shall be deemed to be accepted by Lessee.

IV.  COMMENCEMENT AND TERM OF ORDER
     ------------------------------

     An Order for an individual unit of Equipment or Software shall be binding
from the date it is accepted by Lessor.  Monthly rental as to each unit of
Equipment and Software shall commence fourteen (14) days after shipment
(hereinafter referred to as the "Commencement Date") and shall be set forth on
the initial lease invoice.  Monthly rental for a Custom System Order (as defined
in Article XXVI), if applicable, shall commence thirty (30) days after shipment
(hereinafter referred to as the

                                      -2-
<PAGE>
 
"Commencement Date").  The lease term shall continue for the number of full
months set forth on the Order, commencing on the first day of the month
following the Commencement Date.

     The Order may be renewed for an extended term in accordance with Lessor's
policies in effect at time of the Order's expiration.  Either party must notify
the other in writing at least sixty (60) days prior to expiration of the lease
term of its decision to either renew the Order or terminate any or all of the
Equipment and Software leased thereunder.  Without such notice, the Order shall
continue at the same rate and under the same conditions until such sixty (60)
day notice is given by either party.

     Notwithstanding that the Order contemplates the lease term set forth on the
face of the Order, it is agreed that if Lessee is a governmental entity and is
fiscally funded, continuance of the Order for said term is dependent upon the
annual legislative approval of funding.  Lessee agrees to utilize its best
efforts to assure funding for the continuance of the Order; however, if fiscal
funding is denied, Lessee may terminate the Order by providing Lessor with
written notice as outlined in this provision.

     Upon termination by expiration or otherwise of each Order, Lessee shall, at
Lessee's expense, disconnect the Equipment or de-install the Software and allow
Lessor to enter Lessee's premises to pack and ship the Equipment and Software.
Such Equipment and Software returned to Lessor shall be in the same condition as
delivered by Lessor, reasonable wear and tear excepted and capable of meeting
all recertification requirements.  If Lessor is not allowed to remove the
Equipment and Software as noted within two (2) weeks after the effective date of
Lessee's notice of termination, such termination shall be void, and the lease
shall continue in full force and effect until new notice is given followed by
removal of Equipment and Software in accordance with this paragraph on the
original terms thereof or the terms of any renewal previously agreed upon by the
Lessor, as applicable.

V.   CHARGES AND PAYMENT
     -------------------

     Lessee shall pay to Lessor, the monthly rate set forth on an Order during
each month of the term of such Order.  The monthly lease rate shall be Lessor's
published rates which are in effect at the time that the Equipment or Software
is ordered.  Payments are due monthly, in advance on the first day of each
calendar month.  The Equipment furnished hereunder may be new, remanufactured or
contain used components at Lessor's option.  If the Commencement Date of each
unit of Equipment leased hereunder is other than the first day of a month, the
first payment due hereunder shall be equal to one thirtieth of the monthly rate
set forth on the Order for each day from and including the Commencement Date
through and including the last day of the month prior to the beginning of the
term and the monthly rate for the full initial month.  Lessor reserves the right
to impose a late payment charge of one and one-half percent (1 1/2%) per month,
but not in excess of the lawful maximum, on any past due balance in the event
Lessee shall fail to pay any charges within fifteen (15) days after same are
due, and Lessee agrees to pay same.  If such rate exceeds the amount authorized
by law in the jurisdiction in which the Equipment or Software is located,
interest shall be computed at the maximum legal rate at that location. Payments
shall be made to the Lessor address stated on each invoice.  Charges for Lessor
services (such as standard handling, installation, engineering costs (if
applicable) and training) shall also be at the

                                      -3-
<PAGE>
 
prevailing rates at time of Order.  Any applicable taxes will be invoiced.  The
Equipment and Software is to be leased for the term selected and is non-
cancelable.

     If a purchase order is required for payment, Lessee agrees to provide the
applicable purchase order number(s) to Lessor.  If no purchase order is required
for payment, Lessee guarantees that payment will not be delayed.

VI.  ASSIGNMENT
     ----------

     Without Lessor's prior written consent, Lessee shall not:  (a) assign,
transfer, pledge, hypothecate, or otherwise dispose of all or any part of
Lessee's right, title or interest in and to this Agreement, any Order, the
Equipment or Software; or (b) sublet or lend the Equipment or Software or permit
it to be used by anyone other than Lessee or Lessee's employees.  Lessor may
sell, assign, grant a security interest or participation in all or any part of
Lessor's right, title or interest in and to this Agreement, any Order and the
Equipment or Software without notice to Lessee, and Lessor's assignee or secured
party may then re-assign such interest without notice to Lessee.  Lessee agrees
that any purchase of all or substantially all of Lessee's assets, any merger or
consolidation into or with Lessee (regardless of whether Lessee is the surviving
entity) or any entity acquiring twenty percent (20%) of Lessee's voting
securities shall be deemed to be a transfer under this Agreement.  Lessee agrees
that any such assignment or re-assignment shall not change Lessee's duties or
obligations under this Agreement or any Order and Lessee hereby consents to any
such assignment or re-assignment.  Each such assignee and/or secured party shall
have all the rights but none of the obligations of Lessor under such Order
unless Lessee is otherwise notified by Lessor.  Lessee shall recognize such
assignments and/or security agreements and agrees that upon notice of such
assignment it shall pay directly to assignee (unless otherwise directed by
assignee) without abatement, deduction or set off all amounts which become due
hereunder and further agrees that it will not assert against assignee any
defense, counterclaim or setoff off any reason whatsoever in any action for
lease payments or possession brought by assignee.  Upon such assignment and
except as may otherwise be provided therein, all references in this Agreement to
Lessor shall include assignee.

VII. NETLEASE
     --------

     Lessee and Lessor acknowledge and agree that each Order constitutes a net
lease with all costs, expenses and liability associated with the Equipment or
Software or its Order to be borne by Lessee unless expressly agreed to the
contrary in writing by Lessor.  Lessee's obligations to pay all monthly rates
and any and all amounts payable by Lessee under any Order shall be absolute and
unconditional and shall not be subject to any abatement, reduction, set-off,
defense, counterclaim, interruption, deferment or recoupment for any reason
whatsoever and that such payments shall be and continue to be payable in all
events.  Without limiting the foregoing, no defect or unfitness of any item of
Equipment or Software shall relieve Lessee of its obligations to make rental
payments, pay any other sum when due or otherwise perform any other obligation
due to Lessor and its successors and assigns under this Agreement.  Nothing
contained herein shall affect Lessee's rights to bring an action against Lessor
of any breach of Lessor's obligation hereunder.

                                      -4-
<PAGE>
 
VIII. TITLE AND LOCATION
      ------------------

      The Equipment and Software is and shall remain Lessor's personal property
irrespective of its manner of attachment to realty or its use.  Nothing
contained in any Order shall give or convey to Lessee any right, title or
interest in or to the Equipment or Software, except as a Lessee as set forth
therein and Lessee represents and agrees that Lessee shall hold the Equipment
and Software subject and subordinate to the rights of Lessor.

      Lessor is hereby authorized by Lessee, at Lessee's expense, to cause this
Agreement, any Order, or any statement or other instrument in respect of any
Order as may be required or permitted by law showing the interest of Lessor, in
the Equipment or Software to be filed and Lessee appoints Lessor as its
attorney-in-fact to execute and file on behalf of Lessee any UCC financing
statements and amendments Lessor deems advisable to secure the interests of
Lessor.  Without limiting the foregoing, Lessee shall execute one or more
financing statements, in form and substance satisfactory to Lessor, covering all
Equipment or Software leased to Lessee pursuant to this Agreement.  The parties
have agreed that a photographic copy or other reproduction of this Agreement,
either together with or in lieu of an appropriate form under the UCC, is
sufficient as a financing statement for purposes of filing and perfection under
the UCC.  Any filing of such financing statements or any public recordation of
this Agreement is intended by the parties solely to protect the interest to
Lessor and Lessee, and no such filing or recordation shall in any manner imply
or be construed as implying that the relationship of Lessor to Lessee with
respect to this Agreement or to the Equipment or Software is anything other than
that of a personal property lessor to a personal property lessee.

      Lessee shall request Lessor's consent, in writing, at least fifteen (15)
days before Lessee intends to move any of the Equipment or Software from its
original "ship to" location.  Lessor's response to such request shall be in
writing and its consent shall not be unreasonably withheld.  Lessee shall pay
all costs and expenses for filing additional UCC financing statements in
connection with moving the Equipment or Software.  Lessee agrees to provide
Lessor with fifteen (15) days written notice of its intention to change its name
or corporate identity or structure, by merger, consolidation, reorganization or
otherwise and to pay all costs and expenses for filing additional UCC financing
statements in connection therewith. In the event Lessee fails to comply with
this paragraph or the preceding paragraph, Lessee agrees to indemnify Lessor for
any losses or damages Lessor incurs thereby.

      Upon Lessor's request Lessee will provide landlord's waivers permitting
Lessor to have access to the Equipment and Software in the event of a default by
Lessee hereunder and such other provisions as Lessor may reasonably request.

      Lessee shall, at its expense, protect and defend Lessor's title against
all persons claiming against or through Lessee and shall at all times keep the
Equipment or Software free and clear from any legal process, liens or
encumbrances whatsoever (except any placed thereon by Lessor) and shall give
Lessor immediate written notice thereof and shall indemnify and hold Lessor
harmless from and against any loss caused thereby.

                                      -5-
<PAGE>
 
IX.  INSTALLATION
     ------------

     If R-D is to install Equipment and Software, Lessee shall, at its expense:
provide proper site environment according to site preparation guidelines;
provide voice telephone line and number for installer; ensure that Telco circuit
installation is complete; provide immediate access to site and Equipment and
Software to be installed; provide R-D on-site personnel with application
assistance during installation; provide AC power requirements within ten (10)
feet of equipment location; connect and verify operation of equipment not
provided by R-D; and provide central site configuration support for remote only
installations.

     R-D's Equipment and Software installation service will consist of field
activities required to accomplish the set-up and connection of R-D supplied
Equipment and Software at a Customer location. The principal period of
installation is 9:00 a.m. to 5:00 p.m., Monday through Friday, local time,
excluding R-D holidays.

     Equipment and Software installation service includes:  unpacking and
inspection of the Equipment; placement of Equipment; inter-rack and device
cabling; testing AC power and power application to Equipment; configuring the
Equipment and Software for connectivity; connecting Telco dial, dedicated and/or
dial back-up lines to Equipment; conducting test with distant end if central
site is supported; notifying Customer of any Telco problem or problem with
Equipment or Software not provided by R-D; and providing reasonable cutover
support to ensure passage of live data, if contiguous with installation.

     R-D installation service does not include: site surveys; relocating or
installation of equipment, software or cables not provided by R-D; configuring
or reconfiguring customer DTE or Software, running cables under floors, above
ceilings or through walls; problem diagnosis of Telco circuits; network taps;
central site configuration support for a remote-only installation; nonproductive
time on-site through no fault of R-D; and additional trips to site required
through no fault of R-D.

     Services not included under Equipment or Software installation service may
be performed with prior agreement between the parties at the Time and Material
rates for such services in effect at the time of request.

X.   WARRANTY AND REMEDY
     -------------------

     1.  Warranty
         --------

         Lessor warrants all Equipment obtained hereunder to be free from
         defects in material and workmanship in normal service and under normal
         conditions for one (1) year from date of the initial invoice, and to
         conform to its standard specifications at the time of Order. Lessor
         warrants the Software (if applicable) obtained hereunder will conform
         to its specification at the time it is received by Lessee. THE
         FOREGOING WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES EXPRESSED,
         IMPLIED, OR

                                      -6-
<PAGE>
 
         STATUTORY, INCLUDING WARRANTY OF MERCHANTABILITY OR FITNESS FOR A
         PARTICULAR PURPOSE. THIS WARRANTY IS VOID AS TO EQUIPMENT AND SOFTWARE
         LOCATED OUTSIDE OF THE UNITED STATES OF AMERICA.

     2.  Remedy
         ------

         Should a unit of Equipment fail in normal service and under normal
         conditions through no fault of Lessee during the warranty period,
         Lessee shall return the failed unit at Lessee's expense to Lessor's
         point of origin facility. Lessor shall either repair the unit at the
         factory or furnish a used, refurbished replacement unit for Lessee. No
         charges will be made for repair or replacement of the unit. Lessee
         shall connect and adjust the unit in accordance with accompanying
         instructions. Each repaired or replacement unit of Equipment is
         warranted (as set forth above) for sixty (60) days from the date of
         shipment of such repaired unit, or the remaining portion of the
         original Equipment's warranty, whichever is longer. Lessee agrees to
         pay Lessor's then standard time and material charges for repairs made
         outside of those covered by the Warranty. For any nonconformance of the
         Software (if applicable) to its specification which significantly
         affects performance and is reported to Lessor by Lessee, in writing,
         during the initial ninety (90) days following receipt by Lessee of the
         Software, Lessor shall provide an analysis of the problem and provide a
         workable solution. Lessee agrees to pay Lessor's then current Software
         charges for analysis and efforts to obtain workable solutions provided
         outside of those covered by the Warranty. Lessee agrees that it will in
         no event, alter, modify, repair, disassemble, or adjust the Equipment
         or Software obtained hereby, except in accordance with Lessor
         instructions. Lessor's obligations hereunder are contingent upon proper
         storage, installation, use and maintenance and are limited to: (1)
         repair, or at its option, replacement (as described herein above) of
         any parts or Equipment when Lessor determines that the Equipment does
         not conform to the Warranty; (2) analyzing and providing a workable
         solution to Software problems when Lessor determines that the
         nonconformance significantly affects performance in accordance with its
         specifications. Maintenance of Software, as used herein, is the
         implementation by Lessee of Software revisions provided by Lessor.
         Revisions consist of improvements of specified programs. THE FOREGOING
         CONSTITUTES LESSEE'S SOLE AND EXCLUSIVE REMEDY AND IS IN LIEU OF ANY
         AND ALL OTHER REMEDIES WHICH MAY BE AVAILABLE TO LESSEE AND IS SUBJECT
         IN ADDITION TO THE LIMITATIONS SET FORTH IN SECTION XIX.

XI.  CARE, USE AND MAINTENANCE
     -------------------------

     Lessee shall, at its sole expense and at all times during the term of each
Order, maintain the Equipment and Software in good operating order, repair,
condition and appearance and protect the Equipment and Software from
deterioration, other than normal wear and tear.  Lessee shall not use the
Equipment or Software for any purpose other than that for which it was designed.
Lessee shall, at its

                                      -7-
<PAGE>
 
sole expense, enter into and maintain in force, for the term of each Order, a
maintenance agreement on the Equipment and Software.

XII. SOFTWARE LICENSE
     ----------------

     1.  Lessor hereby grants to Lessee a revocable, nonexclusive license to use
         a copy of the Software only in object code form, and only on a single
         designated processing unit for Lessee's own internal use, except that
         Lessee may execute the Software on another processing unit on a
         temporary basis during a malfunction which prevents execution of the
         Software on the existing processing unit. Lessee agrees not to copy
         Software in whole or in part without the written consent of Lessor
         except Lessee may maintain an archival copy of the Software for back-up
         purposes. Lessee agrees to reproduce any copyright and/or
         confidentiality notices on any copy of the Software or any portion
         thereof made by Lessee. Additional copies of Software required by
         Lessee for its use must be licensed from Lessor.

     2.  Lessee agrees to maintain complete and accurate records which identify
         the type and location of the Software. Within thirty (30) days after
         receiving a request from Lessor, Lessee shall provide copies of the
         applicable records to Lessor.

     3.  Title to the Software shall not pass to Lessee. This license may not
         assigned, sublicensed, or otherwise transferred by Lessee, except that
         Lessee may transfer the license to a transferee and such transferee
         will have the sole benefit of the Software as transferred from Lessee
         provided that Lessee gives Lessor prior written notice of such transfer
         and transferee agrees in writing to be bound under this license to the
         same degree as Lessee.

     4.  The term of an individual units license shall be from the date of
         Lessor's acceptance of an individual Order for Software until
         expiration of the term set forth on the individual Order or upon any
         default of Lessee of any term, covenant or obligation under this
         Agreement. This license may be renewed for additional one (1) or
         multiple year terms provided both parties agree to such renewal in
         writing at least sixty (60) days prior to the expiration of the initial
         term or renewal term. Such renewal shall be in accordance with Lessor's
         standard pricing policies in effect at time of renewal. Lessee agrees
         that upon termination or expiration of term of individual Orders placed
         under license, Lessee will discontinue use of the Software and shall
         certify in writing within three (3) days of termination of this license
         that the Software and all copies thereof have been returned to Lessor
         or destroyed.

     5.  Lessee acknowledges that the Software supplied by Lessor constitutes
         Lessor's and/or it's suppliers trade secrets and agrees to treat all
         Software as confidential and proprietary.

                                      -8-
<PAGE>
 
      6. Lessee shall not, without prior written permission of Lessor, transfer,
         disclose or otherwise provide the programs to any person outside of
         Lessee's organization.

      7. Lessee shall not, without prior written permission of Lessor, modify,
         reverse assemble or reverse compile any of the Software.

      8. Lessee agrees that it shall thoroughly safeguard the confidentiality of
         the Software supplied by Lessor, and in no event shall it be to a
         lesser extent that Lessee safeguards its own proprietary information.
         Lessee agrees that access to such Software will be given only to
         employees who require access in the course of Lessee's business and
         such employees will be informed of the confidential nature thereof and
         will be required to observe provisions of confidence as set forth
         herein.

      9. If Lessee exercises the purchase conversion (set forth in Article XXX,
         below) the Software license granted to Lessee herein shall remain in
         effect pursuant to the terms and conditions set forth herein.

XIII. SYSTEM RESPONSIBILITY
      ---------------------

      Lessor has no responsibility as to the use or application of the Equipment
and/or Software. Lessee assumes full responsibility for data entry, data
maintenance and the functional adequacy of the Equipment and/or Software
configurations as applied in the installation and for all system analysis and
system engineering work.

XIV.  TAXES
      -----

      Lessee and Lessor acknowledge and agree that the liability for all taxes
associated with the Equipment or Software or its Order will be borne by Lessee
unless expressly agreed to the contrary in writing by Lessor.  Lessee's
obligations to pay all taxes shall be absolute and unconditional and shall not
be subject to any abatement, reduction, defense or counterclaim except and only
to the extent that Lessee claims lawful tax exemptions and provides Lessor with
valid exemption certificates on or before the execution of such Order.

      Notwithstanding the foregoing, Lessee and Lessor further acknowledge and
agree that Lessor shall be responsible for filing personal property tax returns
in respect of the Equipment or Software under the lease hereunder, unless
expressly agreed to the contrary in writing by Lessor, and shall bill Lessee for
such taxes incurred.

XV.   FORCE MAJEURE
      -------------

      Lessor shall not be considered in default in performance of its
obligations hereunder if performance of such obligations to provide, repair or
install the Equipment and Software is prevented or delayed by acts of God or
government, labor disputes, failure or delay of transportation, or by vendors

                                      -9-
<PAGE>
 
or subcontractors, or any other similar cause or causes beyond its reasonable
control.  No such occurrence shall excuse the Lessee's performance of its
obligations hereunder.  Time of performance of either party's obligations
hereunder shall be extended by the time period reasonably necessary to overcome
the effects of such force majeure occurrences.

XVI. PATENT INDEMNITY
     ----------------

     Lessor will defend, at its own expense, any action brought against Lessee
to the extent that it is based upon a claim that Lessor provided Equipment or
Software infringes any patent, trade secret or copyright and Lessor will pay
costs and monetary damages finally awarded against Lessee in any such actions
which are attributable to such claim.

     Such defense and liability is conditioned on and limited by: (a) Lessor
being notified promptly in writing by Lessee of any such action; (b) Lessor
having sole control of the defense and all negotiations for settlement of such
action; (c) the damage award liability of Lessor not exceeding the purchase
price for such infringing Lessor provided Equipment or Software; and (d) Lessee
providing all available information, assistance and authority to enable Lessor
to defend, negotiate and settle such action.

     Should such Equipment or Software become, or in Lessor's opinion be likely
to become, the subject to a claim of infringement or the use thereof become
restricted by a final non-appealable Court awarded injunction, Lessee shall
permit Lessor, at Lessor's option and expense, the right to either: (a) procure
for Lessee the right to continue using such Equipment or Software; (b) replace
or modify such Equipment or Software so it is free from infringement or
injunction provided that the same function is performed by the replacement or
modified Equipment or Software; or (c) recover such Equipment or Software from
Lessee, in which latter case, the only rights and liabilities between Lessor and
Lessee are that:  (i) the lease shall be void as to the Equipment or Software on
the date of recovery; and (ii) Lessor has the right to collect lease payments,
if any, due from Lessee for Lessee's possession of such Equipment or Software up
through the date of Lessor's recovery thereof.

     Lessor shall have no liability to Lessee under any provision of this clause
with respect to any claim of infringement which is based upon the:

     (1) Equipment or Software based on specifications furnished by Lessee; or

     (2) combination or utilization of Equipment or Software furnished hereunder
         with equipment or software not provided by Lessor; or

     (3) modification by Lessee of Equipment or Software furnished hereunder.

     The foregoing expresses the entire liability of Lessor for patent, trade
secret or copyright infringement by Lessor Equipment or Software delivered to
Lessee.

                                     -10-
<PAGE>
 
XVII.  DEFAULT
       -------

       Failure of Lessee to make payments or to perform any other condition of
this Agreement shall constitute breach of the affected Order(s) placed
hereunder.

       In addition, the occurrence of any of the following events shall
constitute a breach of all Orders placed hereunder: (1) a receiver, trustee or
liquidator of Customer is appointed for any of its properties or assets; (2)
Customer becomes insolvent or admits in writing its inability to pay its debts
as they mature; (3) Customer makes a general assignment for the benefit of
creditors; (4) a petition for the reorganization of Customer or an arrangement
with its creditors, or readjustment of its debt or its dissolution or
liquidation or similar relief is filed by or against Customer under any law or
statute; (5) Customer ceases doing business or commences dissolution or
liquidation.

       In case of breach, Lessor may cancel the defaulted Order(s), declare the
entire amount of the unpaid commitment and any other charges immediately due and
payable and use all available remedies to take possession and remove Equipment
and Software with all costs, including attorneys' fees, to be borne by Lessee.
Lessor's right to recover possession of the Equipment and Software is in
addition to all other available remedies at law or in equity.

       Each Order by Lessee placed under this Agreement shall be treated as a
separate contract and default by either party arising out of a particular Order
shall not constitute or be deemed to constitute a default of any other Order
under this Agreement.

XVIII. SEVERABILITY
       ------------

       If any provision or provisions of this Agreement shall be held to be
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions shall not in any way be affected or impaired thereby,
provided such provisions still express the intent of the parties.  If the intent
of the parties cannot be preserved, the Agreement shall either be renegotiated
or rendered null and void.

XIX.   LIMITATION OF LIABILITY
       -----------------------

       LESSOR SHALL NOT BE LIABLE FOR ANY INDIRECT, INCIDENTAL, SPECIAL OR
CONSEQUENTIAL DAMAGES, INCLUDING BUT NOT LIMITED TO LOSS OF PROFITS OR REVENUE,
LOSS OR USE OF THE EQUIPMENT OR SOFTWARE OR ANY ASSOCIATED EQUIPMENT OF SOFTWARE
OR COST OF SUBSTITUTED FACILITIES, EQUIPMENT, SOFTWARE OR SERVICES WHICH ARISE
OUT OF PERFORMANCE OR FAILURE TO PERFORM ANY OBLIGATION CONTAINED WITHIN THIS
AGREEMENT, OR OUT OF NEGLIGENCE IN THE COURSE OF SUCH PERFORMANCE, WHETHER THE
CLAIM FOR DAMAGES IS BASED IN CONTRACT, TORT (INCLUDING NEGLIGENCE), STRICT
LIABILITY OR OTHERWISE.

                                     -11-
<PAGE>
 
      EXCEPT FOR CLAIMS FOR PERSONAL INJURY OR FOR DAMAGE TO REAL OR TANGIBLE
PERSONAL PROPERTY TO THE EXTENT CAUSED BY LESSOR'S FAULT OR NEGLIGENCE, LESSOR'S
MAXIMUM LIABILITY TO LESSEE FOR ANY CLAIM FOR DAMAGES RELATING TO LESSOR'S
PERFORMANCE OR NONPERFORMANCE UNDER THIS AGREEMENT SHALL BE LIMITED TO $100,000.

XX.   GOVERNING LAW: FORUM
      --------------------

      This Agreement shall be governed and construed in accordance with the laws
of the State of Florida.  The parties hereby consent and submit to the exclusive
jurisdiction of the appropriate state or federal court serving Broward County,
Florida, as to any dispute or controversy arising either directly or indirectly,
under or in connection with this Agreement.

XXI.  WAIVER
      ------

      1.  No waiver by either party of any default shall operate as a waiver of
any other default or of the same default on a future occasion.  No delay, course
of dealing or omission on the part of either party in exercising any right or
remedy shall operate as a waiver thereof, and no single or partial exercise by
either party of any right or remedy shall preclude any other or further exercise
thereof or the exercise of any other right or remedy.

      2.  Lessee hereby specifically waives any and all its rights and remedies
conferred upon Lessee by UCC Sections 2A - 208 through UCC 2A - 222, including
(without limitation) Lessee's rights to (i) cancel or repudiate this Agreement,
(ii) reject or revoke acceptance of any Equipment or Software, (iii) recover
damages from Lessor for breach of warranty or for any other reason, (iv) claim a
security interest in any rejected property in Lessee's possession or control,
(v) deduct from rental payments all or any part of any claimed damages resulting
from Lessor's default under this Agreement, (vi) accept partial delivery of the
Equipment or Software, (vii) "cover" by making any purchase or lease of other
property in substitution for property due from Lessor, (viii) recover from the
Lessor any general, special, incidental or consequential damages, for any reason
whatsoever, and (ix) seek specific performance, replevin or the like for any of
the Equipment or Software.  To the extent permitted by applicable law, Lessee
also hereby waives any rights now or hereafter conferred by statute or otherwise
which may require Lessor to sell, lease or otherwise use any Equipment or
Software in mitigation of Lessor's damages or which may otherwise limit or
modify any of Lessor's rights or remedies hereunder including any other rights
set forth in Article 2A of the Uniform Commercial Code.  Nothing in this lease
shall be construed as a waiver of Lessee's right to seek damages or other
remedies on account of Lessor's failure to perform its obligations under this
Agreement.

XXII. INSURANCE
      ---------

      Lessee shall, at its own expense, and at all times during the term of an
individual Order keep the Equipment and Software insured against all risks of
loss or damage from every cause whatsoever for not less than the then current
purchase price of the Equipment or Software, provided that the amount

                                     -12-
<PAGE>
 
of such insurance shall be sufficient so that neither Lessor or Lessee shall be
considered a co-insurer. Lessee shall also carry public liability insurance
covering both personal injury and property damage caused by the Equipment or
Software.  All such policies of insurance shall name Lessor as loss payee or
additional insured as the case may be.  Lessee shall deliver to Lessor a copy of
such certificates of insurance.  Each insurer shall agree by endorsement upon
each policy issued by it or by independent instrument furnished with such policy
to Lessor, that it shall give Lessor no less than thirty (30) days written
notice before any such policy shall be materially altered or canceled.  Lessee
hereby appoints Lessor as Lessee's attorney-in-fact to make claim for, receive
payment of, and execute and endorse all documents, checks or drafts for loss or
damage under any such policies of insurance.

XXIII. RISK OF LOSS
       ------------

       Lessee shall bear the entire risk of loss, theft, damage or destruction
of the Equipment and Software from any cause whatsoever (except Lessor's
negligence) from the time shipment is received by Lessee until return shipment
is received in Sunrise, Florida by Lessor. For purposes of this provision the
value of the Equipment and Software shall be the purchase price set forth on the
Order.

XXIV.  GOVERNMENT OBLIGATIONS
       ----------------------

       Lessee warrants that it is, and will remain, in compliance with all
export requirements, including, but not limited to, the requirements of the
Export Administration Act and regulations, the Arms Export Control Act and
regulations, and any orders and licenses issued thereunder. Such requirements
include, but are not limited to, obtaining all proper authorizations or licenses
from the Department of Commerce or the Department of State for the export or re-
export of any item, product, article, commodity or technical data. Lessee
additionally warrants that it has not been, and is not currently, debarred or
suspended from or otherwise prohibited or impaired from exporting, re-exporting,
receiving, purchasing, procuring, or otherwise obtaining any item, product,
article, commodity, or technical data regulated by any agency of the government
of the United States. Lessee agrees to indemnify Lessor and hold Lessor harmless
from any costs, penalties, or other losses caused by, or related to, any
violation of the warranties contained in this Agreement.

XXV.   INTENTION OF PARTIES
       --------------------

       It is the intention of Lessor and Lessee that any lease Orders placed
under this Agreement will be characterized as "true leases" and not "financing
leases" or "leases intended for security".

XXVI.  CUSTOM SYSTEMS
       --------------

       Any changes in orders which include specially-configured Equipment
("Custom Systems") will result in a minimum reconfiguration charge by Lessor to
Lessee of at least five hundred dollars ($500).

                                     -13-
<PAGE>
 
XXVII.  BINDING NATURE
        --------------

        Each order shall be binding upon and shall inure to the benefit of
Lessor, Lessee and their respective successors, legal representatives and
assigns.

XXVIII. FURTHER ASSURANCES
        ------------------

        Lessee shall comply with all applicable laws, ordinances, rules and
regulations and Lessee shall obtain any and all permits, licenses,
authorizations and/or certificates that may be required in any jurisdiction or
by any regulatory or administrative agency in connection with the use and/or
operation of the Equipment or Software.

        Lessee agrees that, upon the request by Lessor and in connection with
the execution and delivery of this Agreement or in connection with each Order,
Lessee shall furnish documents as Lessor may reasonably require, including but
not limited to audited financial statements and certificates of acceptance.

XXIX.   QUIET ENJOYMENT
        ---------------

        Lessor hereby agrees and covenants, so long as no default has occurred
and is continuing, that Lessee shall have, hold and quietly enjoy, subject to
this Agreement, the Equipment and every unit and part thereof during the term of
this Agreement.

XXX.    PURCHASE OPTION FOR LEASED EQUIPMENT
        ------------------------------------

        Lessee shall at all times during the term of a lease order issued
pursuant to this Agreement have an option to purchase the Equipment then leased
thereunder by paying Lessor the purchase conversion price. The purchase
conversion price shall be calculated in accordance with the following table:

<TABLE>
<CAPTION>
 
                    TERM        PURCHASE CONVERSION
                                   FACTOR (PCF)
                    <S>         <C>
                      12               62%
                      24               48%   
                      36               31%   
                      48               27%   
                      60               20%   
</TABLE>

     At the end of a lease term, the above percentages can be applied against
the "if sold" value, which was in effect at the time the Equipment was acquired.
In addition to the above, in the event

- ---------------------

   

                                      14
<PAGE>
 
Lessee requires a purchase conversion during the lease term Lessee would also be
responsible for all lease payments until the end of the original lease term.

       Exercise of this option shall in no way relieve Lessee for lease payments
due up to the date of conversion, but not yet paid, on the unit which is being
converted to purchase.  Maintenance terms existing on Equipment converted to
purchase shall remain in effect for the duration of said term.

XXXI.  SUBSTITUTION
       ------------

       Lessor shall have the right, at Lessor's sole option, to replace any or
all BayNetworks equipment provided or to be provided by Lessor pursuant to this
Agreement with comparable equipment manufactured or supplied by Lessor as such
comparable equipment becomes available. After such comparable equipment
manufactured or supplied by Lessor becomes available, Lessor may, at Lessor's
sole option, substitute such comparable equipment for BayNetworks equipment for
any future Order placed by Lessee pursuant to this Agreement.

XXXII. ENTIRE AGREEMENT
       ----------------

       The terms and conditions contained in this Agreement shall be applicable
to all Orders placed on Lessor by Lessee during the effectiveness of this
Agreement whether this Agreement is referenced or not on such Orders. Additional
or different terms contained in Lessee's purchase orders shall not be applicable
to such Orders unless expressly agreed to in writing by Lessor's authorized
representative. This Agreement, including all Orders accepted hereunder,
expresses the entire understanding and agreement of the parties with reference
to the subject matter hereof, and is a complete and exclusive statement of the
terms of this Agreement, and no representations or agreements modifying or
supplementing the terms of this Agreement, including but not limited to Lessee's
purchase order, shall be valid unless in writing and signed by persons
authorized to sign agreements on behalf of both parties.

       IN WITNESS WHEREOF, this Agreement was entered into as of the day and
year first written above.

ACCEPTED:                           ACCEPTED:

Concentric Network Corporation      Racal-Datacom, Inc.
- ---------------------------------   ----------------------------------------   
(Lessee)                            (Lessor)


By:/s/ Michael F. Anthofer          By:/s/ Kathleen Walsh
   ------------------------------      -------------------------------------   

Name: Michael F. Anthofer           Name: Kathleen Walsh
      ---------------------------        -----------------------------------

Title: V.P. & CFO                   Title: Director of Contracts & Proposals
       --------------------------          ---------------------------------

Date: 6-26-96                       Date: 6-26-96
      ---------------------------         ----------------------------------   

                                     -15-

<PAGE>
 
                                                                   EXHIBIT 10.24

                        MASTER ON-SITE MAINTENANCE PLAN
                            AGREEMENT NUMBER CON02C


     This Master On-Site Maintenance Plan agreement (hereinafter referred to as
"Agreement") is entered into this _________24th____________ day of August, 1994,
by and between Concentric Research Corporation, a Florida corporation,
(hereinafter referred to as "Customer"), having its principal place of business
located at 400 Forty-First Street, Bay City, Ml 48708 and Racal-Datacom, Inc., a
Delaware corporation, (hereinafter referred to as "R-D"), having its principal
place of business located at 1601 N. Harrison Parkway, Sunrise, Florida 33323-
2899, organizations duly authorized by law.


                                WITNESSETH THAT

     WHEREAS, R-D is the manufacturer of data communications equipment
(hereinafter referred to as "Equipment") and software (hereinafter referred to
as "Software") which is purchased by or leased to the general public; and,

     WHEREAS, Customer is desirous of establishing a plan (hereinafter referred
to as the "On-Site Maintenance Plan agreement") for on-site maintenance on
Equipment and Software:

and,

     WHEREAS, 100th parties are desirous of establishing the terms and
conditions which shall govern all On-Site Maintenance Plan agreement orders
issued pursuant to this Agreement.

     NOW THEREFORE, in consideration of the covenants, premises and mutual
agreements contained herein, the parties do hereby agree as follows:

I.   TERM OF AGREEMENT
     -----------------

     This Agreement shall commence upon the date first written above and shall
continue for a term of twelve (12) months.  This Agreement shall govern all
Orders (as defined in Article III) placed hereunder provided such Orders are
received by R-D within twelve (12) months beginning upon the date of
commencement of this Agreement.  Thereafter this Agreement shall automatically
renew itself in twelve (12) month increments unless either party notifies the
other of its decision to terminate this Agreement by providing the other party
sixty (60) days written notice prior to the expiration of the period then in
effect.
<PAGE>
 
II.  EQUIPMENT AND SOFTWARE ELIGIBILITY
     ----------------------------------

     Equipment and Software set forth in the published R-D price book as being
supported by the On-Site Maintenance Plan agreement and installed within the 48
contiguous United States and the District of Columbia are eligible for coverage
under the On-Site Maintenance Plan agreement provided herein and will be covered
hereunder if such services are ordered.

III. TERM OF INDIVIDUAL ORDER

     (a)  Leased Equipment and/or Software.  Customer has ordered Basic Coverage
          --------------------------------   -----------------------------------
maintenance coverage for a four (4) year term on R-D Order Number 132450. R-D
- -----------------------------------------------------------------------------
agrees to provide Basic Coverage maintenance coverage at no charge to Customer
- ------------------------------------------------------------------------------
for the initial one (1) year of said four (4) year term for all Equipment set
- -----------------------------------------------------------------------------
forth on said Order. The terms and conditions set forth herein shall govern such
- --------------------------------------------------------------------------------
Order. Such one (1) year free maintenance coverage shall apply only to Equipment
- --------------------------------------------------------------------------------
which is set forth on R-D Order Number 132450 and any applicable replacement
- ----------------------------------------------------------------------------
Equipment for such Order.
- ------------------------ 

     For Equipment ordered subsequent to Order Number 132450, within one (1)
year of the execution of this Agreement or such time as Customer's financing
conditions meet the requirements of Exhibit One to Master Agreement Number
CONO1C, whichever first occurs, (the "Introductory Period"). Customer may elect
to order Basic Coverage maintenance coverage for a four (4) year term and obtain
free coverage for the first year of said term. The payment schedule and order
amount shall be determined at the time of each order is placed during the
Introductory Period.

     For Equipment orders placed after the Introductory Period, Customer and R-D
shall determine the term of the Basic Coverage, if any, and the price and
payment schedule for each respective Order.

     For Equipment not set forth on R-D Order Number 132450, and for ANY
     -------------------------------------------------------------------
Equipment coverage subsequent to the expiration of the one (1) year "no-charge"
- -------------------------------------------------------------------------------
coverage, monthly maintenance payments for Equipment shall be made in accordance
- --------------------------------------------------------------------------------
with Master Agreement Number CON01C.  Upon expiration of the initial lease term
- -----------------------------------   -----------------------------------------
Customer may renew Basic Coverage for each subsequent committed lease term
- --------------------------------------------------------------------------
extension of one (1) year or more by paying R-D's monthly maintenance charges
- -----------------------------------------------------------------------------
for the committed lease term and coverage required in effect at the time of each
- --------------------------------------------------------------------------------
such lease extension.  If Customer does not extend for a committed term.  Basic
- --------------------   --------------------------------------------------------
Coverage services shall be provided on a month-to-month basis. Maintenance
- -------------------------------------------------------------  -----------
payments shall be made for the duration of the initial lease term or renewal
- ----------------------------------------------------------------------------
term, if renewed.  In addition. Customer shall be entitled to Extra Coverage
- ----------------   ---------------------------------------------------------
under the conditions set forth below. and at the charges stated therein.
- ----------------------------------------------------------------------- 

     (b)  Purchased Equipment.  Customer may obtain coverage under this 
          -------------------
Agreement pursuant to the conditions set forth below in one (1) or multiple year
increments immediately following the purchase of a unit of Equipment.  If
Customer converts to purchase a leased unit of Equipment with On-Site
Maintenance Plan agreement coverage, the duration of such On-Site Maintenance
Plan agreement coverage shall be for the remaining term of the original
commitment.  On-Site Maintenance Plan agreement payments for such units shall be
made in accordance with the applicable R-D Order under

                                      -2-
<PAGE>
 
which the Equipment is purchased. Upon expiration of the initial term, Customer
may renew coverage for additional one (1) or multiple year increments by paying
R-D's On-Site Maintenance Plan agreement charges in effect at the time of each
such renewal. For Customers on an annual payment basis, if R-D does not receive
payments within thirty (30) days after notification to Customer of such renewal,
the On-Site Maintenance Plan agreement coverage shall expire. If Customer has
elected to pay the On-Site Maintenance Plan agreement charges on a monthly
basis, the On-Site Maintenance Plan agreement services shall be provided on a
month-to-month basis, until either party notifies the other, with at least
thirty (30) days prior written notification, of its decision to either renew the
order or terminate any or all of the Equipment covered thereunder. R-D reserves
the right to increase the maintenance rates for those units of Equipment and
Software which are on a month-to-month term upon thirty (30) days written
notice.

     (c)  Equipment and Software Eligibility.  At R-D's sole option, R-D may add
          ----------------------------------                                    
or delete Equipment and Software types eligible under the On-Site Maintenance
Plan agreement as provided for hereunder at any time. Deletion of any or all
Equipment and Software types will have no effect on such types of installed
Equipment or Software already covered hereunder, but will rescind Customers
option to extend coverage for such types of installed Equipment and Software
under the terms of "a" and "b" above and will make coverage unavailable for
newly installed Equipment and Software of such types.


IV.  ORDERING PROCEDURE

     Customer shall issue Orders to R-D on R-D's order form or Customer's order
form.  As a minimum, such Orders shall include the following information:

     1.   Description of Equipment or Software to be maintained.

     2.   Quantity of each item of Equipment or Software to be maintained.

     3.   Extent of maintenance required and charges.

     4.   Customer contact for maintenance.

     5.   Billing address and billing contact.

     6.   Location and serial numbers of Equipment.  R-D will acknowledge
          ----------------------------------------                       
acceptance or rejection of orders within fifteen (15) days after receipt of the
order at R-ID, Sunrise, Florida Once accepted. the Order is noncancelable.

V.   COVERAGES PROVIDED
     ------------------

     The On-Site Maintenance Plan agreement provided by R-D to Customer consists
of the following coverages:

                                      -3-
<PAGE>
 
     1.   Basic Coverage

          (A)  Equipment.  For the initial ninety (90) days from Commencement 
               ---------
Date as defined in Section IV of Master Lease Agreement Number CON01("IMP") R-
D's Maintenance shall be twenty-four (24) hours per day, seven (7) days per
week, with no 4 additional charge to Customer. R-D's normal response time for
Customer requests for on-site maintenance received by R-D during the IMP shall
be within H' four (4) hours for Zone A locations and within eight (8) hours for
all other locations.

          Thereafter, the Principal Period of Maintenance ("PPM") shall be 8:00
a.m. to 6:00 p.m., local time, Monday through Friday, excluding R-D holidays. R-
D's normal response time for Customer requests for on-site maintenance received
by R-D during PPM shall be within four (4) PPM hours for Zone A locations and
within eight (8) PPM hours for all other locations. Zone A locations shall be as
listed in R-D's published price book in effect at the time the On-Site
Maintenance Plan agreement services are ordered.

          The Equipment On-Site Maintenance Plan agreement coverage includes
such services as will be provided by R-D, or its authorized representative, to
Customer. For Support Category A Equipment, as set forth in R-ID's published
price book, such services consist of : telephone technical consultation and
troubleshooting available 24 hours a day, 7 days a week; dial-up test facilities
available for all Equipment possessing dial-up capability; on-call remedial
maintenance during PPM which is required due to the failure of Equipment;
preventive maintenance at R-IDs discretion; and delivery of replacement
Equipment. For Support Category B Equipment, as set forth in R-D's published
price list, such services consist of: telephone technical consultation and
troubleshooting available 8 hours a day, 5 days a week, excluding R-D holidays;
dial-up test facilities available for all Equipment possessing dial-up
capability; on all remedial maintenance during PPM which is required due to
failure of Equipment; preventive maintenance at R-D's discretion; and delivery
of replacement Equipment.

          Engineering or firmware changes deemed mandatory by R-D will be
installed by R-D on replacement units. Customer elected engineering or firmware
changes that are not deemed mandatory by R-D, will be made available to Customer
at the rates set forth in R-D's price book in effect at the time of the request
and are not included in this Agreement.

          (B) Software.  The Software On-Site Maintenance Plan agreement 
              --------
coverage provided by R-D to the Customer will consist of: For Support Category A
Software as set forth in R-D's published price book, Customer access to
available R-D Bulletin Board; telephone technical consultation and
troubleshooting 24 hours a day, 7 days a week; and on-site installation of
Software maintenance releases recommended by R-D during PPM hours. For Support
Category B Software, as set forth in R-D's published price list, Customer access
to available R-D Bulletin Board: telephone technical consultation and
troubleshooting S hours a day, 5 days a week; and copies of Software maintenance
releases. A Software maintenance release shall mean a Software program fix or
improvement that solves a problem or enhances the performance of the Software
but does not necessarily expand the functionality of the Software. The Software
maintenance releases will be provided to Customer by R-D at the time of their
production release. Certain maintenance releases will be made available on R-D's
Electronic Bulletin

                                      -4-
<PAGE>
 
Board service for downtime loading to the Customers Equipment.  Other Software
maintenance releases will be made available to Customer on diskettes. One copy
of each maintenance release will be made available to Customer for each Software
product under maintenance. Each maintenance release is licensed to run only on
the unit under maintenance. For Support Category B Software, Customer shall use
                                                                            ---
its best efforts to implement each revision within sixty (60) days from receipt
- --------------------                               ---------                   
of notice in order to continue Software maintenance coverage.

          R-D shall use its best efforts to provide a workable solution to
Software problems in a timely manner when R-D determines the Software does not
conform to its specification.

          (C) Exclusions.  The following services are outside the scope of Basic
              ----------                                                        
Coverage under this On-Site Maintenance Plan: electrical work external to the
Equipment; repair or replacement work or increase in service time due to fire,
flood, water, wind, lightning, power surges, neglect, misuse; inadequate
electrical power, air conditioning or humidity control; unauthorized persons
modifying, repairing or servicing the unit; and "no trouble found" calls.

     In addition to the above, the following items are considered consumables
and not included as covered parts under this Agreement: cathode ray tubes whose
only problem is burnt phosphor, platens, exterior finishes, fuses, bulbs,
supplies, disk packs and cartridges; and, diskettes.

     2.  Extra Coverage.  Extra Coverage is such services as will be provided by
         --------------                                                         
R-D, or its authorized representative, and for which Customer shall be
separately billed at the hourly rate of [*] per hour, with a two (2) hour
minimum, for services performed. Extra Coverage consists of: those services
described above as "Basic Coverage" which are requested by the Customer to be
performed by R-D outside PPM hours; any maintenance service which the Customer
requests and R-D agrees to perform which is not included in "Basic Coverage",
e.g., relocation of Equipment or Software, utilization of R-D personnel to
supervise or perform the packaging and crating of Equipment or Software, etc.;
any service call resulting from or required by the "Exclusions" set forth above;
and any service performed when R-D determines that the cause of Equipment or
Software failure was not the result of failure in Equipment, Software or
communication facilities provided by R-D.

     Subsequent to the IMP set forth above, Customer may request R-D to perform
Basic Coverage services outside the PPM set forth above. Customer agrees to pay
an hourly rate equal to [*] per hour, with a two (2) hour minimum, any Basic
Coverage services performed outside the PPM provided R-D 4, responded to such
request within four (4) hours for any Zone A locations or within eight (8) hours
for any other locations. In the event R-D does not respond to such Basic
Coverage service request within the time frames set forth herein, Customer shall
have no obligation to pay R-D the hourly rate. Zone A locations shall be as
listed in R-D's published price book in effect at the time of request.


- --------------------
     [*]Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.

                                      -5-
<PAGE>
 
Any other Extra Coverage services performed hereunder shall be invoiced, and
paid, at the hourly rate of [*] per hour, regardless of the time such service
was performed.

     The monthly On-Site Maintenance Plan agreement prices for the Initial Order
placed hereunder is set forth on Order Number 132450. Such prices are for Basic
Coverage as set forth in Article III.a, Term of Individual Order, Leased
Equipment and/or Software. Thereafter, Customer may elect to order maintenance
coverage at rates, and for specific term lengths, to be mutually determined at
time of Order.

VI.  CUSTOMER ASSISTANCE
     -------------------

     Customer shall, in all cases where Customer personnel is available, and at
no charge to R-D, perform such non-skilled checks and tests as reasonably
required by R-D's written instructions provided in Installation and Operation
Manuals and by telephone from R-D Field Support Centers. These tests shall not
require Customer to furnish specialized test equipment.

VII. FREEDOM OF ACCESS
     -----------------

     Customer agrees that R-D or its authorized representative, shall have
reasonable and free access to the Equipment and Software. My unreasonable delays
or return service calls required because of denial of reasonable and free access
to the Equipment or Software will be separately billed to the Customer as "Extra
Coverage".

VIII. CUSTOMER RESPONSIBILITIES
      -------------------------

     In regard to each unit of Equipment and Software covered by this Agreement,
Customer agrees to prevent unauthorized adjustment, repairs or modifications,
and to ensure that the Equipment and Software is utilized in accordance with the
applicable R-D published specifications or the specifications set forth in
Exhibit 3 of Master Agreement Number CON01C. In the event that either one of
these responsibilities is not fulfilled, R-D shall have the right to immediately
withdraw the affected Equipment and Software from coverage under this Agreement.

IX.  SYSTEM RESPONSIBILITY
     ---------------------

     R-D agrees the Equipment will meet its published specifications in the
     ----------------------------------------------------------------------
application proposed by R-D as set forth in Exhibit 3 of Master Agreement Number
- --------------------------------------------------------------------------------
CON01C.  The Customer assumes full responsibility for data entry, data
- ------                                                                
maintenance, the functional adequacy of the Equipment and Software configuration
as applied in the installation and for all system analysis and system
engineering work except as warranted in Article XIV of Master Agreement Number
                 -------------------------------------------------------------
CON01C.
- ------ 


- --------------------
     [*]Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission.  Confidential treatment has been
requested with respect to the omitted portions.

                                      -6-
<PAGE>
 
X.   MOVEMENT OF EQUIPMENT
     ---------------------

     The On-Site Maintenance Plan agreement charges specified on an order apply
only to the Equipment at the location specified on the order. Equipment moved to
any area serviced by R-D is eligible for continued coverage in accordance with
R-D's rates and terms then in effect for that location. Customer is responsible
for proper movement, risk of loss or damage to the Equipment or Software and all
associated costs.

     R-D shall be the sole point of contact with regard to all maintenance
performed under this Agreement. In the event additional charges accrue against
or are paid by R-D as a result of direct Customer request to any third party for
maintenance services, or any maintenance services provided because of causes
other than normal wear and tear (i.e. unauthorized attempts to repair, maintain
or modify the Equipment or Software, fault or negligence of customer, operator
error, improper use or misuse of the Equipment or Software; causes external to
the Equipment or Software, such as but not limited to fluctuations of humidity
or temperature), Customer shall reimburse R-D an amount equal to any such
charges.

XI.  CREDIT FOR EQUIPMENT DOWNTIME
     -----------------------------

     If for reasons solely within its control, 9-0 fails to restore a failed
unit of Equipment to operating condition within twenty-four (24) hours
subsequent to a "Normal Response Time", then Customer shall be entitled to a
credit for that unit of Equipment for that period of time and each subsequent
full twenty-four (24) hour period during which the failure continues. The amount
of such credit for a leased unit shall be 1/30th of the monthly lease rate and
for a purchased unit shall be 1/30th or R-D's published thirty-six (36) month
lease rate for the affected unit. Irrespective of any such claims, Customer
shall continue to make any payments otherwise due R-D under the Order for such
Equipment and services, nor shall such claim(s) entitle Customer to cancel such
order except as provided for in Article XIV.3 of Master Agreement Number CON01C.
      ------------------------------------------------------------------------- 

XII. FORCE MAJEURE
     -------------

     Neither party shall be considered in default in performance of its
obligations hereunder if performance of such obligations is prevented or delayed
by acts of God or government, labor disputes, failure or delay of
transportation, or by vendors or subcontractors, or any other similar cause or
causes beyond the reasonable control of the other party. Time of performance of
either parties obligations hereunder shall be extended by the time period
reasonably necessary to overcome the effects of such force majeure occurrences.

XIII. LIMITATION OF LIABILITY
      -----------------------

     NEITHER CUSTOMER OR R-D SHALL BE LIABLE FOR ANY INDIRECT, INCIDENTAL,
SPECIAL, OR CONSEQUENTIAL DAMAGES, INCLUDING BUT NOT LIMITED TO LOSS OF PROFITS
OR REVENUE, LOSS OF USE OF THE EQUIPMENT OR SOFTWARE, OR ANY

                                      -7-
<PAGE>
 
ASSOCIATED EQUIPMENT AND SOFTWARE, OR COST OF SUBSTITUTED FACILITIES, EQUIPMENT
OR SERVICES WHICH ARISE OUT OF PERFORMANCE OR FAILURE TO PERFORM ANY OBLIGATION
CONTAINED WITHIN THIS AGREEMENT OR OUT OF NEGLIGENCE IN THE COURSE OF SUCH
PERFORMANCE, WHETHER THE CLAIM FOR DAMAGES IS BASED IN CONTRACT, TORT (INCLUDING
NEGLIGENCE), STRICT LIABILITY OR OTHERWISE.

     Except for claims for personal injury or for damage to real or tangible
personal property to the extent caused by R-D's fault or negligence, R-D's
maximum liability to Customer for any claim for damages relating to R-D's
performance or non-performance under this Agreement shall be limited to 
$200,000.

XIV. PAYMENT TERMS
     -------------

     (a) Recurring Costs:  All charges for billable services performed under
         ---------------   -------------------------------------------------
this Agreement shall be invoiced upon completion.  The initial invoice for Basic
- ------------------------------------------------   -----------------------------
Coverage for Equipment covered during the Initial Year shall be in accordance
- -----------------------------------------------------------------------------
with the Article III.a entitled Term of Individual Order. Leased Equipment
- --------------------------------------------------------------------------
and/or Software, set forth above.  Payments are due monthly in advance, on the
- --------------------------------                                               
first day of each month. First payment due for services ordered hereunder shall
include 1/30th of the month's payment for each day elapsing since commencement.

     (b) Nonrecurring Costs: Payments are net thirty (30) days from date of
                                              -----------------------------
invoice.  All charges for billable services performed hereunder shall be
- -------                                                                 
invoiced upon completion.

     (c) For purchased items, if the net discounted value of accumulative
billings for maintenance services is less than $600 a year, or $50 a month,
payment will be made on an annual payment basis only.

     (d) Payments shall be made to R-D at address stated on each invoice.

     (e) If a purchase order is required for payment of any services (including
Extra Coverage) performed hereunder, Customer agrees to provide the applicable
purchase order number(s).  Customer guarantees that payment will not be delayed.

XV.  DEFAULT
     -------

     Failure of Customer to make payments as defined herein or to perform any
other condition of this Agreement shall constitute breach of the affected
order(s) issued hereunder.  The failure by Customer, within sixty (60) days
after the commencement of any proceeding against Customer seeking

                                      -8-
<PAGE>
 
any reorganization, arrangement, composition, readjustment, liquidation,
dissolution, or similar relief under any present or future statute, law,
regulation, to obtain the dismissal of such proceeding or within sixty (60) days
after the appointment without the consent or acquiescence of Customer, of any
trustee, receiver or liquidation of Customer or of all or any substantial part
of the properties of Customer to vacate such appointment shall constitute breach
of all orders placed hereunder.  In case of breach, R-D may cancel the defaulted
Order(s), declare the entire amount of any unpaid commitments and any other
charges to be immediately due and payable.

     R-D reserves the right to impose a late payment charge of one and one-half
percent (1-1/2%) per month, but not in excess of the lawful maximum on any past
due balance in the event Customer shall fail to pay any charges within fifteen
(15) business days after same are due, and Customer agrees to pay same.
     --------                                                          

XVI. TAXES AND FEES
     --------------

     Customer covenants and agrees to pay when due or reimburse and indemnify
and hold R-D harmless from and against all taxes, fees or other charges of any
nature whatsoever (together with any related interest or penalties not arising
from negligence on the part of R-D) now or hereafter imposed or assessed against
R-D, Customer or the Equipment or Software by any Federal, State, County or
local governmental authority upon or with respect to the Equipment or Software
or upon the ordering, ownership, delivery, possession, use or operation, return
or other disposition thereof or upon the rents, receipts or earnings arising
therefrom or upon or with respect to any order (excepting only Federal, State
and local taxes based on or measured by the net income of R-D). If Customer
warrants that the Order shall be exempt from sales tax, it is the Customer's
responsibility to provide R-D with valid sales tax exemption certificates within
thirty (30) days of date Order is placed.

XVII. REQUESTS FOR ON-SITE MAINTENANCE SERVICE
      ----------------------------------------

     All requests for service shall be initiated by an authorized representative
of Customer. The request for service shall be directed to the Technical
Assistance Center for support Category A Equipment and Software and to the
Regional Service Office for support Category A Equipment and Software. The
applicable offices are set forth in Schedule A, attached hereto and incorporated
herein. Each service request shall contain the following information:

          Name and address of Equipment and Software users      
          Name of the person to be contacted and telephone number
          Equipment and Software type and serial number         
          Equipment and Software location                       
          Description of problem                                 

XVIII. REPLACED EQUIPMENT OR PARTS
       ---------------------------

                                      -9-
<PAGE>
 
     When replacement Equipment, or any part thereof, is provided to the
Customer, the replaced Equipment, or part thereof, shall become the property of
R-D. Replacement parts shall be either new parts or parts equivalent in
performance to new parts when used with the Equipment.

XIX. GOVERNING LAW: FORUM
     --------------------

     This Agreement shall be governed and construed in accordance with the laws
of the State of Florida. The parties hereby consent and submit to the exclusive
jurisdiction of the appropriate state or federal courts serving Broward County,
Florida, as to any dispute or controversy arising either directly or indirectly,
under or in connection with this Agreement.

XX.  WAIVER
     ------

     No waiver by either party of any default shall operate as a waiver of any
other default or of the same default on a future occasion. No delay, course of
dealing or omission on the part of either party in exercising any right or
remedy shall operate as a waiver thereof, and no single or partial exercise by
either party of any right or remedy shall preclude any other or further exercise
thereof or the exercise of any other right or remedy.

XXI. SEVERABILITY
     ------------

     Each order by Customer hereunder shall be treated as a separate contract
and default by either party arising out of a particular order shall not
constitute or be deemed to constitute a default of any other Order under this
Agreement.

XXII. NOTICES
      -------

     Any notices or communications given or required under this Agreement shall
be sufficiently given if delivered personally, in writing or sent by telex or
facsimile, federal express, registered or certified mail, postage prepaid, to
the other party at the following address:

               TO:  Racal-Datacom, Inc.                      
                    P.O. Box 407044                          
                    Ft. Lauderdale, FL 33340                 
                    Attn:  Director of Contracts             
                    cc: Sr. Vice President and General Counsel
                                                             
               TO:  Concentric Research Corporation          
                    400 Forty-First Street                   
                    Bay City, MI 48708                       
                                                             
                    With a copy to:                          
                    Susan Cook, Esq.                          

                                      -10-
<PAGE>
 
                    Lambert, Leser, Cook, Schmidt and Giunta, P.C.
                    309 Davidson Building, P.O. Box 835
                    Bay City, MI 48707

     Such notice or other communications shall be deemed received (a) on the
date delivered, if delivered personally; or (b) upon receipt, if sent by telex
or facsimile, federal express or (c) three (3) business days after being sent,
if sent registered or certified mail.

XXIII. ENTIRE AGREEMENT
       ----------------

     The terms and conditions contained in this Agreement shall be applicable to
all orders placed on R-D by Customer during the effectiveness of this Agreement
whether referenced or not on such orders. Additional or different terms
contained in Customers purchase orders shall not be applicable to such orders
unless expressly agreed to in writing by R-D's authorized representative.  This
Agreement expresses the entire understanding and agreement of the parties, with
reference to the subject matter hereof, and is a complete and exclusive
statement of the terms of this Agreement, and no representations or agreements
modifying or supplementing the terms of this Agreement including but not limited
to Customers purchase order and R-D's order acknowledgment form, shall be valid
unless in writing, signed by persons authorized to sign agreements on behalf of
both parties.

     IN WITNESS WHEREOF, this Agreement was entered into as of the day and year
first written above.

ACCEPTED:                              ACCEPTED:

CONCENTRIC RESEARCH CORP.              RACAL-DATACOM, INC.

Customer                               (R-D)

By: /s/ Donald Schutt                  By: /s/ Kathleen Walsh
    --------------------------------       ---------------------------------

Name: Donald Schutt                    Name: Kathleen Walsh
      ------------------------------         -------------------------------

Title: CEP                             Title: Director of Contracts
       -----------------------------          ------------------------------

Date: 8/24/94                          Date: September 16, 1994
      ------------------------------         -------------------------------

                                      -11-
<PAGE>
 
                                  SCHEDULE A

For support Category A units:
TECHNICAL ASSISTANCE CENTER
OFFICE LOCATION
- ---------------
400 Embassy Row
Suite 300
Atlanta, GA 30328
 
<TABLE> 
<CAPTION> 

For support Category B units:
REGIONAL SUPPORT OFFICE
LOCATION                             ASSIGNED TERRITORY
- --------                             ------------------
<S>                                  <C>            <C> 
Northeast Region                     
- ----------------                     Connecticut
Racal-Datacom, Inc.                  Delaware       New York
1010 Campus Drive West               Maine          Pennsylvania
Morganville, New Jersey 07751        Massachusetts  Rhode Island
                                     New Hampshire  Vermont
 
Central Region
- --------------
Midwest Office                       Illinois       Nebraska
Racal-Datacom, Inc.                  Indiana        North Dakota
3455 Salt Creek Lane, Suite 100      Iowa           Ohio
Arlington Heights, Illinois 60005    Kansas         Oklahoma
                                     Kentucky       South Dakota
                                     Michigan       Texas
 
Southwest Office                     Minnesota      West Virginia
Racal-Datacom, Inc.                  Missouri       Wisconsin
12092 Forestgate Drive
Dallas, Texas 75243
      
 
Southeast Region                     
- ----------------                     Alabama        Mississippi
Racal-Datacom, Inc.                  Arkansas       North Carolina
503 Oak Place, Suite 590             Florida        South Carolina
Atlanta, Georgia 30349               Georgia        Tennessee
                                     Louisiana      Virginia
                                     Maryland       Washington, DC
 
Westcoast Region                     
- ----------------                     Alaska         Montana
Racal-Datacom, Inc.                  Arizona        Nevada
600 S. Placentia Avenue              California     Oregon
Placentia, California 92670          Colorado       Utah
                                     Hawaii         Washington
                                     Idaho          Wyoming
</TABLE>

<PAGE>
 
                                                                   EXHIBIT 10.31


                       INTERNET ACCESS SERVICES AGREEMENT


     THIS INTERNET ACCESS SERVICES AGREEMENT is effective as of  August 1, 1995
(the "Effective Date"), by and between Intuit Inc., a Delaware corporation
("Intuit"), and Concentric Network Corporation, a Florida corporation formerly
known as Concentric Research Corporation ("CNC"), with reference to the
following facts:

                                    RECITALS
                                    --------

     A.   Intuit creates, markets and distributes certain financial, tax and
other software products and services.

     B.   CNC is an on-line telecommunications services and Internet access
provider that offers various services through the CNC Network, as defined below,
including non-Internet telecommunications, access to the Internet, electronic
mail, USENET news, Telnet and various Internet Protocols, as defined below.

     C.   Intuit desires to offer Internet Services on the terms and conditions
set forth in this Agreement to persons who license the Products defined below
("Customers") by (i) incorporating the Internet Features into the Products and
(ii) obtaining the CNC Services from CNC to permit access to the Internet, and
CNC is willing to perform the Development Project and provide the CNC Services
to support Intuit's provision of the Internet Services to the Customers and
other communications requirements.

     D.   The parties hereto agree and acknowledge that this Agreement
memorializes actions that occurred, or obligations undertaken, on or after the
Effective Date, and reflects their agreement with respect to future performance
as set forth herein.

     NOW, THEREFORE, for valuable consideration, the parties hereto agree as
follows:

     1.   Definitions.  In addition to any other capitalized terms defined in
          -----------                                                        
this Agreement, the following terms shall have the meanings provided below:

          1.1  "Access" shall mean the provision of telecommunications transport
and/or an interconnection to the Internet Services via the CNC Network using a
POP Access or a Non-POP Access, as the case may be.

          1.2  "Agreement" shall mean this Internet Access Services Agreement,
including its exhibits and attachments, all by this reference incorporated into
and made a part hereof.

          1.3  "Browser" shall mean the client access software including the
dialer, registration wizard, image viewer, TCP/IP stack and other software
permitting the establishment of a point-to-point protocol (PPP) connection with
the Internet through the CNC Network.

          1.4  "Commitment Agreements" shall mean that certain Stand-By
Financing Agreement and that certain Warrant Issuance Agreement by and between
the parties hereto, and certain CNC shareholders, dated as of the Execution Date
and their related agreements.

          1.5  "CNC Code" shall mean the POP, login server, registration server,
encryption, data security and other software, including object code and source
code, described or referred to
<PAGE>
 
in this Agreement, and developed by CNC to support the Internet Services
provided by Intuit, including any related documentation.

          1.6  "CNC Network" shall mean the computing, information services,
hardware, software (including the CNC Code), telecommunications, access and
provisioning provided by CNC as further described in this Agreement and in that
certain CNC Private Placement Memorandum dated November 3, 1995, as such network
may be modified, improved and expanded during the Term of this Agreement.

          1.7  "CNC Services" shall mean any and all of the services rendered
and support that CNC is required to provide under the terms of this Agreement
including, but not limited to, those relating to the provision of Internet
Services, Non-Internet Traffic Services, customer support, billing and
collection, and ongoing System development.

          1.8  "Customer Charge(s)" shall mean the charges set by Intuit from
time to time and payable by the Customers for the Internet Services as further
described in Section 4.3.

          1.9  "Customer Information" shall mean all the information and records
collected, processed or compiled by CNC, including (without limitation) lists of
Customer names, addresses, and telephone numbers; registration, credit and
financial information; information respecting Customer needs, usage and demands;
product; entry point; and such other marketing information as may be useful to
or desired by Intuit to promote or improve the Internet Services or its
Products.

          1.10 "Development Project" shall mean the activities of CNC and Intuit
to develop and test the CNC Network's ability to support the Internet Services
as further described in Section 3 and Exhibit "B".
                                      ----------- 

          1.11 "Full Internet Service(s)" shall mean a service that provides a
Customer with access to the Intuit Areas via the CNC Network and unrestricted
access via the CNC Network to all generally accessible locations and services on
the Internet.

          1.12 "Information Statements" shall mean monthly statements prepared
and made available by CNC to the Customers and Intuit for on-line viewing on the
CNC Network pursuant to Section 4.3 and Exhibit "D" attached hereto.
                                        -----------                 

          1.13 "Internet" shall mean the network of computers, information
systems and communications systems using the TCP/IP protocols and commonly
referred to as the Internet.

          1.14 "Internet Connection Services" shall mean providing general
access to the Intuit Areas to persons who are connected to the Internet via any
mechanism other than through the Access provided by CNC.

          1.15 "Internet Features" shall mean the Browser, CNC Services,
topology, schematics, hardware and software, and other systems and features
offered by or through Intuit in conjunction with the Products that enable a
Customer to gain access to and use the Internet Services through the Products.

          1.16 "Internet Protocols" shall mean file transfer protocol (FTP),
Internet Relay Chat (IRC), World Wide Web access and other current and future
protocols.

          1.17 "Internet Services" shall mean the Full Internet Services, the
Restricted Internet Services and the Internet Connection Services.

                                       2
<PAGE>
 
          1.18 "Intuit Areas" shall mean locations on various host computers,
including those which may be operated by CNC, which provide various information
and services to various Customers accessing such host computers by using
Internet Protocols including, without limitation, World Wide Web sites operated
by Intuit.  Intuit will determine, in its sole discretion, which information and
services to provide to which Customers in the Intuit Areas.

          1.19 "Intuit Systems" shall mean Intuit's host computers which are not
providing the Internet Areas.

          1.20 "Network Plan" shall mean the CNC Network deployment plan
described in Exhibit "A".
             ----------- 

          1.21 "Network Specifications" shall mean the description, performance
standards, topology and specifications for the CNC Network as described in this
Agreement.

          1.22 "Non-Internet Traffic Services" shall mean telecommunications
access other than continuous session-based services using Internet Protocols
such as the World Wide Web, e.g., the burst disconnect asynchronous
                            ----                                   
communications of banking data is non-Internet traffic.

          1.23 "Non-POP Access" shall mean that a Customer in a given geographic
location may gain access to the CNC Network through a long distance or 800#
phone number, and not through a local POP.

          1.24 "Performance Standards" shall mean the established target and
minimum performance measurements for the CNC Network and the CNC Services as
described in this Agreement.

          1.25 "POP" or "Point of Presence" shall mean the hardware (such as
modems, terminal servers and routers), software, networks and telecommunications
connections operated by CNC at a local facility or site through which a Customer
may gain access to the Internet through a dial-up TCP/IP link with the CNC
Network.

          1.26 "POP Access" shall mean that a Customer in a given geographic
location can gain access to the Internet through a link with the CNC Network
through a local phone number. CNC may provide POP Access either through a
physical POP or through any mechanism by which a local-access telephone
connection is re-routed to the CNC Network at no charge to the Customer.

          1.27 "Port" shall mean a modem connection on a terminal server at a
POP.

          1.28 "Products" shall mean Intuit's Quicken personal financial
software product, Quickbooks small business accounting software product,
ProSeries professional tax preparation software product, and TurboTax personal
tax preparation software product, and such other Intuit software products as
shall be added to the coverage of this Agreement at the sole discretion of
Intuit by an addendum hereto executed and delivered between CNC and Intuit.

          1.29 "Restricted Internet Service(s)" shall mean a service that
provides a Customer with access via the CNC Network to various Intuit Areas and
to certain other Internet locations and services as Intuit shall specifically
authorize for such Customer from time to time.

          1.30 "Service Charge(s)" shall mean the charges for CNC Services to be
paid by Intuit to CNC as provided in Section 4.3 hereof.

                                       3
<PAGE>
 
          1.31 "Term" shall mean from and after the Effective Date until the
expiration or termination of the Service Term.

          1.32 "URL" or "Uniform Resource Location" shall mean the address of a
resource on the Internet, e.g., "http://www.cris.com".
                          ----                        

          1.33 Certain other terms used herein are defined in the following
provisions:
<TABLE>
<CAPTION>
 
                Term                  Section
                ----                  -------
<S>                                   <C>
 
          Effective Date              Preamble
 
          Customer(s)                 Recital "C"
 
          Integrated Browser                  2.4
 
          Alternate Services                  2.4
 
          System                              3.1
 
          Release Date                        4.1
 
          Service Term                        4.1
 
          Contract Year                       4.1
 
          Customer Support Center           4.2.4
 
          Confidential Information          5.1.1
 
          License Agreement                   5.4
 
          Transition Period                   6.4

          Execution Date                    Signature Page

          Minimum Performance Standard(s)   Exhibit "A"

          Target Performance Standard(s)    Exhibit "A"

          Monthly Reconciliation            Exhibit "D"
</TABLE> 

     2.   Concept of Operations and General Agreement.
          ------------------------------------------- 

          2.1  Concept of Operations.  Intuit desires to make available the
               ---------------------                                       
Internet Services to its Customers by the distribution of certain Internet
Features with any or all of the Products as Intuit may determine in its sole
discretion, and to obtain Non-Internet Traffic Services from CNC from time to
time.  As a part of the CNC Services, CNC shall provide the following:  Customer
logon and registration in a format provided or approved by Intuit, service
upgrades, account management, credit approvals, Customer billing; reporting
network and infrastructure management, operation and maintenance; Access;
provision of Internet Services and Non-Internet Traffic Services; and

                                       4
<PAGE>
 
customer and technical support.  CNC will charge Intuit for the CNC Services in
accordance with Section 4.3.  Intuit will independently establish its charges to
Customers for the Internet Services, and CNC will bill the Customers on behalf
of Intuit on such terms and conditions as Intuit may determine in its sole
discretion.

          2.2  CNC Network Structure.  The current and proposed structure of the
               ---------------------                                            
CNC Network is described in Exhibit "A" attached hereto.  CNC has established
                            -----------                                      
and is implementing the Network Plan to expand, improve and enhance the
capabilities of the CNC Network to facilitate its support of Intuit.

          2.3  General Agreement.  Intuit and CNC will perform the Development
               -----------------                                              
Project pursuant to Section 3 to support CNC's ability to provide the Internet
Services.  Thereafter, subject to the terms of this Agreement, CNC will provide
during the Service Term, and Intuit will use, the CNC Services in the
continental United States and Canada so long as CNC is not in breach of this
Agreement.  CNC will perform the CNC Services in accordance with the highest
professional and technical standards for services of this nature, and will
strictly comply with any related performance capabilities, accuracy,
completeness, characteristics, specifications, configurations, standards and
requirements set forth in this Agreement.  However, notwithstanding anything to
the contrary in this Agreement, Intuit shall have the right to determine which,
if any, Internet Services to include with each of its Products.

          2.4  Qualified Exclusivity.  During the Service Term (except during
               ---------------------                                         
any Transition Period), Intuit will offer any Intuit-branded Internet access
services to Customers in the continental United States and Canada using Internet
browsers integrated into the Products exclusively through CNC.  However, the
foregoing exclusivity provision shall not apply to high band width access
services (such as interactive television, cable modem, ISDN, or other services
which operate at speeds greater than 28.8 Kbps).  Furthermore, the foregoing
exclusivity provision shall not prevent or prohibit any of the following
activities, provided that Intuit does not provide an Integrated Browser in
conjunction with such activities: (a) Intuit from providing general access to
the Intuit Areas from, by or through the Internet or any other networks, content
areas, content providers, on-line services or access service providers (for the
purposes of this Section 2.4, collectively referred to as "Alternate Services")
(b) Intuit's customers from using any other Alternate Services in any manner
they choose, (c) Intuit from maintaining content areas on or through other
Alternate Services, (d) Intuit from providing links to the Intuit Areas from, by
or through other Alternate Services, or (e) Intuit from engaging in marketing or
promotional activities (including but not limited to joint product distribution)
with other Alternate Services.  An Integrated Browser shall be defined as an
Internet browser which is both (a) distributed with an Intuit Product and (b)
integrated with such Product so that it is installed via the same installation
routine and can be launched from directly within such Product. Upon (i) the
termination or expiration of this Agreement or (ii) CNC's Net Working Capital
(as defined in the Stand-By Financing Agreement) falling below one million
dollars ($1,000,000), the foregoing exclusivity provision shall cease to be
effective and in any event shall not apply to any Transition Period during
which Intuit uses CNC Services pursuant to Section 6.4.

     3.   System Development and Tests.
          ---------------------------- 

          3.1  System Development.  In accordance with the Development Project
               ------------------                                             
Work Statement attached hereto as Exhibit "B", the parties shall perform their
                                  -----------                                 
respective Development Project obligations (at their own cost) to develop,
implement, execute, integrate and test the software code (including the CNC
Code), hardware and software systems, procedures and installation to develop an
overall system to offer the Internet Services (collectively, the "System").
During the Term of this Agreement, CNC (i) warrants that the CNC Code shall meet
all its specifications to support Intuit's provision of the Internet Services,
(ii) will provide to Intuit at no

                                       5
<PAGE>
 
charge unlimited telephone access to CNC's technical support staff to obtain
assistance relating to the CNC Code, and (iii) will develop and deliver to
Intuit at no charge any maintenance or feature releases, and related
documentation, to correct a programming error or other defect or to increase or
enhance the features or functionality of the CNC Code which CNC makes available
as a standard feature of its standard commercial release during the Term.

          3.2  System Tests.  Upon completion of the development phase, Intuit
               ------------                                                   
and CNC shall jointly test the System and CNC Network to ensure compliance with
the Network Specifications and the Performance Standards.  The tests and related
acceptance procedures for the System and CNC Network are set forth in the
Development Project Work Statement.

     4.   Post-Development Provision of Services.
          -------------------------------------- 

          4.1  Introduction of Services.  Once the development and testing of
               ------------------------                                      
the CNC Services and the System is completed to Intuit's satisfaction, then
Intuit may announce the availability of the Internet Services in connection with
the release of one or more of the Products in a manner that Intuit shall
determine.  If Intuit elects to offer the availability of the Internet Services,
the date that Intuit sets for the release of its first Product offering the
Internet Services shall be the "Release Date," which the parties acknowledge is
October 26, 1995.  For an initial period of three years from and after the
Release Date plus the length of any Transition Period pursuant to Section 6.4
(together, the "Service Term"), CNC shall provide the CNC Services and Intuit
shall pay for the CNC Services in accordance with this Agreement.  Thereafter,
the Service Term may be extended at the option of Intuit in successive one-year
periods up to a maximum of three additional years, provided that Intuit notifies
CNC in writing of Intuit's election to extend this Agreement at least 120 days
prior to the expiration of the Service Term then in effect.  Each twelve month
period during the Service Term commencing on the Release Date, or its
anniversary, shall be known as a "Contract Year," i.e., First Contract Year,
                                                  ----                      
Second Contract Year, etc.
                      --- 

          4.2  Ongoing Operations and Customer Support.  With respect to
               ---------------------------------------                  
Internet Services offered by Intuit, CNC shall perform the following obligations
during the Service Term:

          4.2.1     Customer Logon, Registration and Upgrades.  CNC shall logon,
                    -----------------------------------------                   
register and upgrade Customers in accordance with the procedures set forth in
                                                                             
Exhibit "C" attached hereto or as the parties may otherwise agree.  CNC shall
- -----------                                                                  
collect and maintain Customer Information in a form available for electronic
access by Intuit and as Intuit may from time to time direct.  CNC shall
periodically provide to Intuit Customer  Information collected by CNC in a scope
and format reasonably requested by Intuit.

          4.2.2     Customer Information.  Notwithstanding anything to the
                    --------------------                                  
contrary in this Agreement, Intuit shall be the sole owner of all Customer
Information, including any and all associated intellectual property rights. CNC
acknowledges that (i) the Customer Information is a "trade secret" under the
Uniform Trade Secrets Act of California, (ii) Intuit has maintained and intends
to maintain the Customer Information as proprietary and confidential
information, and (iii) the unauthorized use, loss or disclosure of such Customer
Information will cause irreparable harm to Intuit.  Therefore, notwithstanding
anything to the contrary in this Agreement, during and after the Term hereof,
CNC shall (i) use and copy the Customer Information only for purposes reasonably
related to and as permitted by this Agreement, and not, directly or indirectly,
use the Customer Information for its benefit or the benefit of anyone else, or
in any way against Intuit's interest, and (ii) diligently safeguard the Customer
Information and shall not permit or authorize the disclosure of any of the
Customer Information to any third person or entity, either directly or
indirectly, without Intuit's prior written authorization.  Notwithstanding the
above, CNC shall have the right to maintain and use general network usage
statistics including the usage by the Intuit Customers, provided that

                                       6
<PAGE>
 
such aggregated data does not contain information on individual Customers.  CNC
shall return or destroy (and provide a written officer's certificate to such
effect) any Customer Information, and all copies thereof, in any form upon
Intuit's request and, in any event, upon the termination or expiration of this
Agreement.  CNC acknowledges that a breach of this section would cause
irreparable harm to Intuit, which would entitle Intuit to seek the relief
described in Section 5.1.3.

          4.2.3     Customer Account Management. CNC shall use reasonable
                    ---------------------------                          
efforts to make detailed usage and billing information available in electronic
format on line to each Customer and Intuit.  CNC is responsible for verifying
all Customer credit and billings, and bears the risk of loss for any subsequent
credits given to Customers where such credits are caused by CNC's failure to
perform in accordance with this Agreement.

          4.2.4     CNC Customer Support Center.  CNC shall establish and
                    ---------------------------                          
maintain, or cause to be established and maintained, facilities, equipment,
staffing and programming, collectively making up the "Customer Support Center,"
as necessary to collect and maintain the Customer Information, and provide
Internet Services and technical and account support to the Customers and Intuit.
In this regard, CNC shall do each of the following:

          4.2.4.1   Plan for, provide, maintain, operate, and manage the
Customer Support Center, including space, equipment, utilities, personnel and
systems. The Customer Support Center shall include a telephonic help desk for
Customers, which will be staffed by knowledgeable CNC employees and/or
subcontractors capable of providing assistance relating to Access and use of the
Internet Services. Such telephone assistance shall be available to Customers on
a continuous basis, twenty-four (24) hours per day, seven (7) days per week.

          4.2.4.2   Plan for, acquire, install, maintain, repair, operate,
manage, and expand, improve, or replace hardware as necessary or appropriate to
support and operate the Customer Support Center, including any computer systems,
direct access storage devices, tape units, communications control units, and
associated equipment.

          4.2.4.3   Plan for, obtain, install, maintain, operate, and enhance
the operating system software, languages, utilities, and other system software
as necessary or appropriate to support and operate the Customer Support Center.

          4.2.4.4   Maintain the Customer Information, including related
Customer Information structures; provide back-up measures, recovery procedures,
file maintenance and expansion, updating, tape storage, management, and control
of space utilization; and provide related data security and administration.

          4.2.4.5   Establish and administer change controls, problem
resolution management, and provide planning, availability management,
performance reporting, implementation procedures, and other controls.

          4.2.4.6   Notify Intuit reasonably in advance of making any
material changes to the Customer Support Center or CNC Network.

          4.2.4.7   Meet as requested with Intuit and evaluate the Customer
Support Center and related Customer technical support services with a view
toward enhancing them to meet the needs and demands of Customers.

          4.2.5     CNC Network Performance, Maintenance and Upgrades.
                    ------------------------------------------------- 

                                       7
<PAGE>
 
          4.2.5.1   CNC Network Performance.  During the Term, the CNC Network
                    -----------------------                                   
shall perform at a level satisfying or exceeding the Performance Standards.
During the Service Term, upon request, CNC will meet with Intuit to review the
network performance. Subsequent to such a review, Intuit may request that CNC
(i) improve and enhance the CNC Services and operation of the CNC Network
(including increasing capacity and coverage by the addition of Ports and POPs)
in excess of the improvements and enhancements set forth in the Network Plan, or
(ii) develop and maintain the CNC Network so that it is at least comparable to
and competitive with the functions and features available from other Internet
access providers.  If CNC declines to make improvements reasonably requested by
Intuit in a timely manner, Intuit may elect to terminate the Agreement as
provided in Section 6.1.  Periodic reports on the CNC Network's operations and
performance shall be developed and provided to Intuit as it may reasonably
request, in addition to any other reports required by this Agreement.

          4.2.5.2   General Network Maintenance.  During the Service Term, CNC
                    ---------------------------                     
 shall do each of the following:

          (a) Plan for, obtain, provide, operate, and maintain the CNC Network
facilities and hardware, whether at its central sites or at POPs, hubs or remote
nodal sites or central location sites, including ordering, installing and
maintaining owned or leased telecommunications lines, backbones, tail circuits,
dial-switched services and satellite services, modems, multiplexers,
concentrators, control computers, switching devices, and satellite transmitting
and receiving equipment.

          (b) Develop and maintain Internet Protocol interfaces, and
configuration, and provide capacity planning, technology evaluation and
selection, communications tariff evaluation, topology planning, network control
planning and related software development, interface standards development,
protocol conversion and development of protocol converters.

          (c) Operate and maintain the CNC Network on a twenty-four hour a day
seven days a week basis, including monitoring the network; provide necessary
repairs, network back-up, problem resolution, and testing; and provide for
recovery of the CNC Network and the physical security of the CNC Network and its
related operating facilities.

          (d) Provide and maintain any interfaces between the Intuit Areas and
the Customers (provided that Intuit is responsible for the cost of any direct
phone lines between CNC and Intuit).

          (e) Provide library and address maintenance, management, and
administration and such other resources as may be reasonably necessary or
appropriate for the development and maintenance of the database containing the
Customer Information.

          4.2.5.3  Telephone Assistance Provided to Intuit.  CNC shall maintain
                   ---------------------------------------      
a technical help desk for Intuit, which will be staffed by knowledgeable CNC
employees capable of providing technical assistance regarding the CNC Services,
CNC Network and Customer Information. Such telephone assistance shall be
available to Intuit on a continuous basis, twenty-four (24) hours per day, seven
(7) days per week. The help desk also will administer resolution of network
problems encountered by Intuit and the Customers and keep Intuit apprised of the
efforts to be taken to remedy such problems until complete restoration of
service.

          4.2.5.4  Annual Service Plans.  At least ninety days before the 
                   --------------------                       
beginning of each Contract Year, Intuit shall prepare and deliver to CNC a non-
binding services

                                       8
<PAGE>
 
forecast that identifies Intuit's estimated usage and demand requirements for
such period, including estimated capacity requirements and resource use in terms
(for example) of the estimated number of Customers and usage volumes, and
additional Customer Information that will be required by Intuit.  CNC and Intuit
shall meet and confer for the purpose of refining the services forecast on a
basis that reasonably takes into account the Customers' expected needs and CNC's
existing and planned resources.  CNC shall use its reasonable best efforts to
make available the resources  at the level required to support Intuit's
forecasted annual services.

          4.2.5.5  Priorities and Response Time.  In the event of any 
                   ----------------------------                  
unscheduled downtime of the CNC Network or the System, or problems affecting
the functioning or productivity thereof or the provision of Internet Services or
the CNC Services, CNC shall provide installation and emergency maintenance and
repair service as determined in accordance with the following priority
classifications:

          (a) Priority 1:  Any problem that interrupts the continued
availability of the CNC Network or CNC Services to Intuit or the Customers, or
causes severe user disservice.  In such event, CNC shall take immediate
corrective action regarding the problem, on a continuous basis, twenty-four
hours per day, seven days per week, until the problem is resolved.

          (b) Priority 2:  A critical problem involving any application or
system of the CNC Network that does not yet, but could if not corrected,
interrupt the continued availability of the CNC Services or cause severe user
disservice.  CNC shall take immediate corrective action regarding the problem,
on a continuous basis during normal business hours (eight hours per day, five
days per week), until the problem is resolved.

          (c) Priority 3:  A problem that does not impair the availability of
the CNC Services or CNC Network significantly, because temporary procedures are
in place to provide acceptable alternative operation of functionality.  CNC
shall schedule and work on the class of problem on a time-available basis.

          4.2.5.6  Scheduled Downtime.  CNC shall provide at least ten days 
                   ------------------                             
advance written notice to Intuit and affected Customers of any
scheduled downtime of the CNC Network or other events that may affect the
availability of the CNC Services.  CNC shall schedule major upgrades, downtime,
repairs, or maintenance to the CNC Network during times mutually agreeable with
Intuit.

           4.3     Charges for CNC Services.
                   ------------------------ 

          4.3.1    Quarterly Usage Forecasts.  Each month, Intuit shall provide
                   -------------------------                                   
CNC with a non-binding monthly usage forecast for the subsequent three calendar
months containing the information set forth in Exhibit "D" (e.g. in October,
                                               -----------  ----            
Intuit would provide a usage forecast for each of November, December and
January).  The forecasts will be based, in part, on the usage data made
available by CNC.

            4.3.2  Service and Customer Charges.
                   ---------------------------- 

          4.3.2.1  Service Charges.  The Service Charges are the fees 
                   ---------------                              
payable by Intuit to CNC for the CNC Services based on the Customers' connect
time. If Intuit systematically and fundamentally alters the way it offers and/or
prices Internet access to its Customers, the parties will negotiate in good
faith regarding appropriate adjustments to this Agreement. CNC and Intuit shall,
pursuant to the procedures in Exhibit "D", perform the Monthly Reconciliation to
                              -----------
determine the Service Charges payable by Intuit. Any delinquent payments by

                                       9
<PAGE>
 
either party under this Agreement shall bear interest at the rate of 1.5% per
month commencing thirty days after such payment is due.

          4.3.2.2  Most Favorable Treatment.  During the Service Term but 
                   ------------------------                     
excluding the Transition Period, CNC warrants to Intuit on a continuing basis
that the rates and terms under this Agreement for the CNC Services shall not
exceed those offered by CNC to other CNC customers purchasing the same or fewer
quantities of connect hours for the same or similar services. If CNC offers to
any other similarly situated customer similar work, services, or products at
lesser rates or on more favorable terms, CNC shall immediately notify Intuit of
such circumstances and, thereafter, CNC shall charge Intuit such lesser service
charges and offer such more favorable terms for all remaining CNC Services under
this Agreement.

          4.3.3     Customer Charges, Billing and Collection.  The Customer
                    ----------------------------------------               
Charges are the fees payable by the Customers for the Internet Services provided
by Intuit.  Intuit reserves the right, exercised in its sole discretion, to
charge and may charge the Customers additional fees (i.e., an amount greater
                                                     ----                   
than the Service Charges) for their access to and use of the Internet Services.
The initial procedures for such charges are set forth in Exhibits "B" and  "D"
                                                         ---------------------
hereto.  CNC assumes sole responsibility and risk for establishing credit
accounts, verifying and billing Customers' credit card accounts and billing and
initiating processing for all Customer Charges for the Internet Services as
described in Exhibits "B" and  "D".  Processing fees paid to third parties for
             ---------------------                                            
the purpose of processing credit card, debit card or other payment transactions
shall be Intuit's responsibility.

          4.3.4     Record Keeping and Audits.  CNC shall maintain complete and
                    -------------------------                                  
accurate books, records and accounts relating to the CNC Services and Internet
Services to support and document all charges, billings, mark-up amounts, and
credits, in accordance with standard accounting principles consistently applied
with respect to prior periods.  Intuit's representatives, including any
independent auditor or accounting organization retained by Intuit, shall have
access to such books, records and accounts, upon reasonable notice to CNC, for
purposes of reviewing, verifying and copying such books, records and accounts.
Intuit shall have the right to demand such an audit up to two times in any given
12 month period.  If such an audit discloses an under calculation in excess of
five percent (5%) of the amount payable to Intuit, then CNC shall bear the cost
of such examination, and shall promptly correct the calculation of amounts
payable and pay any underpaid amount, plus interest for delinquent payments as
set forth in Section 4.3.2.1 from the date such amount was due and payable.

          4.3.5     No Other Payment, Etc.  Except as otherwise expressly
                    ---------------------                                
provided in this Agreement, neither party shall be entitled to payment, cost
reimbursement, or other compensation from the other party in respect of its
performance, and each party shall bear all its own expenses incurred in
rendering performance, including facilities, work space, utilities, management,
personnel, communications, clerical, supplies, and the like.

          4.3.6     Taxes.  CNC is responsible for promptly collecting and
                    -----                                                 
paying all federal, state, county, services or other taxes, however designated
and whether levied or based upon the CNC Services, exclusive however of taxes
based on Intuit's net income.

          4.4  Customer Information and CNC Network Security.  CNC shall develop
               ---------------------------------------------                    
and implement systems and procedures to maintain strict security of all Customer
Information (including credit card information).  Guidelines on the security of
such information is set forth in Exhibit "E" attached hereto.  Intuit's
                                 -----------                           
representatives, upon reasonable advance notice to CNC, may conduct periodic
security audits of CNC's sites and the systems relating to the Internet Services
and CNC Services to determine whether the security mechanisms (physical,
processes, etc.) are sufficient to protect the applicable data.
           ---                                                 

                                       10
<PAGE>
 
     5.   Related Covenants.
          ----------------- 

          5.1  Confidential Information.
               ------------------------ 

          5.1.1   Confidential Nature.  During the course of this relationship,
                  -------------------                            
the parties may disclose to the other certain confidential information orally,
in writing or through facility visits, which information may include, but is not
limited to, financial information or projections; lists of and information about
agents, vendors, suppliers, dealers, customers, potential customers, and
statistical and financial information associated therewith; specifications and
uses of products and services; product research; sales, marketing and strategic
plans; pricing policies; products and availability information; and information
otherwise defined as "trade secrets" under the Uniform Trade Secrets Act of
California (collectively, "Confidential Information"); provided, however, that
Confidential Information does not include information that can be documented as
being known within the industry prior to the Effective Date or information that
becomes publicly available thereafter through no breach of this Agreement by any
party hereto. The parties have maintained and will continue to maintain the
Confidential Information as their own private, proprietary and confidential
information and as their business trade secrets. Sometimes this information may
be stamped "Trade Secret," "Confidential," or with a similar designation, but
failure to do so will not in and of itself impair the classification of
information as Confidential Information.

          5.1.2   Restrictions.  The Confidential Information contains
                  ------------                                        
valuable business and technical information and constitutes trade secrets, and
the parties acknowledge that the unauthorized use, loss or disclosure of such
Confidential Information will cause irreparable harm to the owner of such
Confidential Information.  The parties shall use the Confidential Information
only for purposes relative to and as permitted by this Agreement.  During the
Term and for a period of two years thereafter, neither party shall directly or
indirectly use the Confidential Information for its benefit or the benefit of
anyone else, except as otherwise permitted in writing, or in any way against the
other party's interest.  Each party shall diligently safeguard the Confidential
Information and shall not, during the Term and for a period of two years
thereafter, disclose, permit the disclosure of, or authorize the disclosure of
any of the Confidential Information to any third person or entity, either
directly or indirectly, unless prior written authorization is granted by the
owner thereof.  The parties shall not make any copies of any of the Confidential
Information, except as reasonably required to perform its obligations under this
Agreement, and shall return any such Confidential Information including, without
limitation, all notes, memoranda, records, plans, sketches, or other documents,
and all copies thereof, embodying, regarding or derived from any Confidential
Information, upon oral or written request, and, in any event, upon the
termination or expiration of this Agreement.

          5.1.3   Injunctive Relief.  The parties acknowledge that a breach of
                  -----------------                                           
this Section 5.1 would cause irreparable harm to an owning or injured party,
which would not have an adequate remedy at law with respect to disclosure or
threatened disclosure of the Confidential Information.  Therefore, in the event
of a breach or threatened breach of the obligations contained in this Section
5.1, either party is entitled to seek the immediate issuance, without notice,
hearing, or bond, of a temporary restraining order precluding the continuance of
the conduct in question and may pursue other injunctive relief.

          5.2     Publicity.  CNC shall not issue press releases, conduct
                  ---------                                              
promotional efforts or engage in any other publicity of any nature regarding
this Agreement or CNC's relationship with Intuit or disclose any of the terms of
this Agreement without the prior written approval of Intuit, except to the
extent required for regulatory or statutory public reporting purposes.

                                       11
<PAGE>
 
          5.3      Relationship of Parties.  The parties acknowledge and 
                   ----------------------- 
agree that each party has entered into this Agreement as an independent
contractor. Nothing in this Agreement shall be construed as creating any other
relationship between the parties including, but not limited to, any partnership
or joint venture between Intuit and CNC.

          5.4      Grant of License.  Concurrent with the execution and 
                   ----------------
delivery of this Agreement, Intuit and CNC shall execute and deliver a License
Agreement substantially in the form of Exhibit "F" attached hereto (the "License
                                       ----------- 
Agreement").

          5.5      Future Network Services.  CNC acknowledges and agrees that
                   -----------------------
implementation of the CNC Services as contemplated in this Agreement will
require a significant percentage of CNC's available resources. CNC therefore
agrees that from the Effective Date until February 28, 1996, CNC shall not
provide, or enter into any material agreement to provide, telecommunications or
access services to any other companies or engage in any public financing
activities without Intuit's express written consent exercised in its sole
discretion, not to be unreasonably withheld, based on Intuit's evaluation of the
effect of such services or activities on CNC's ability to perform its
obligations under this Agreement.  Intuit shall indicate its consent or lack
thereof within five working days of being provided with sufficient information
to make an informed judgment.

          5.6      Branding of Services.  The Internet Services offered by 
                   -------------------- 
Intuit, directly or indirectly, shall be branded according to Intuit's
directions, i.e., screen logos, written or electronic communications with
            ----
Customers, customer service phone announcements, etc.; provided, however, that
                                                 ----
the welcome pages in the registration process shall provide an attribution that
the network connection services are being provided by and are the responsibility
of CNC. CNC's reproduction or use of any Intuit copyrighted materials,
trademarks or service marks shall be strictly in accordance with the guidelines
provided by Intuit from time to time. CNC hereby acknowledges receipt of
Intuit's current copyright and trademark guidelines. CNC's use of Intuit's
proprietary rights is limited solely in relation to its provision of the CNC
Services pursuant to this Agreement.

          5.7       Compliance With Laws and Regulations.  Each party shall, 
                    ------------------------------------                     
at its own expense, comply with any governmental law, statute, ordinance,
administrative order, rule, or regulation relating to its duties, obligations,
and performance under this Agreement and shall procure all governmental licenses
and pay all fees and other charges required thereby.

          5.8       Appointment of CNC as Billing and Collections Agent.  Intuit
                    ---------------------------------------------------         
hereby appoints CNC as its agent to bill and collect amounts pursuant to the
procedures set forth in this Agreement owing to Intuit from Customers who have
registered to receive Internet Services; provided, however, that such billings,
receivables and amounts shall be the sole property of Intuit.  Intuit may
terminate this appointment and make other arrangements for Customer billing and
collections in its sole discretion.

          5.9       Project Manager and Project Technical Coordinators.  Each 
                    --------------------------------------------------        
party shall designate an initial Project Manager and Project Technical
Coordinator within ten (10) business days of the Effective Date (and such other
managers and coordinators as may be reasonably required), with such changes as
either Party may notify to the other from time to time.

          5.10      Financial Information.  During the Term, CNC shall provide 
                    ---------------------
to Intuit the financial reports and information described in Section 5 of that
certain Warrant Issuance Agreement for Warrants to Purchase Series B Preferred
Stock between the parties hereto.

          6.   Term and Termination.
               -------------------- 

                                       12
<PAGE>
 
               6.1  Termination on Notice for Intuit Dissatisfaction.  If, in
                    ------------------------------------------------         
Intuit's judgment, CNC's performance is not satisfactory for any reason
(including but not limited to network access and reliability, features and
capabilities, host operations, customer satisfaction, programming support,
management strength and financial condition) at any time, Intuit may terminate
this Agreement by providing six month written notice of such intention to
terminate.

               6.2   Immediate Termination by Intuit for CNC Failure to Meet 
                     --------------------------------------------------------
Minimum Performance Standards. If, in any given month, CNC fails to meet the 
- -----------------------------                                                
Minimum Performance Standards for any performance measurement, then Intuit may
terminate this Agreement by providing written notice of such intention to
terminate. Upon receipt of such notice, CNC may immediately provide Intuit with
a detailed corrective action plan and timetable to correct the default and
request a period of 30 days in which to cure the default. Unless Intuit
reasonably believes that CNC cannot or will not promptly and permanently correct
the deficiency and restore the CNC Services, then Intuit will delay the
termination of the Agreement during such 30-day period. If, however, CNC fails
to correct such deficiency during such 30-day period or Intuit subsequently
determines during such period that CNC's proposed corrective action plan will
not be completed within such 30 day period, then Intuit may immediately
terminate the Agreement on further written notice to CNC.

               6.3   Mutual Termination Rights Upon Default and Breach.
                     ------------------------------------------------- 

                     6.3.1 Upon the occurrence of any of the following events of
default, after giving written notice to the defaulting party and following the
completion of the cure period set forth in Section 6.3.2, the non-defaulting
party may declare the other party to be in breach of this Agreement and may
immediately terminate this Agreement:

                             6.3.1.1  the failure of either party substantially
to perform or comply with any material provision of this Agreement;

                             6.3.1.2  the admission in writing by either party
of its inability to pay its debts as they mature, or the making by either party
of an assignment for the benefit of its creditors;

                             6.3.1.3   the party becomes insolvent as evidenced
by the fact that the party is generally not paying its debts as they become due
(unless such debts are the subject of a bona fide dispute) and/or the sum of
such party's debts is greater than all of such party's property valued at fair
market value;

                              6.3.1.4  the filing of a petition under any
bankruptcy act, receivership statute or like law or statute as they now exist or
may be subsequently amended by either party, or the filing of such a petition by
any third party against either party, or the making of an application for a
receiver by either party, where such petition or application is not dismissed or
otherwise favorably resolved within sixty days; or

                              6.3.1.5 in addition to the foregoing, with respect
to CNC, the breach by CNC or any of its majority shareholders of their
respective obligations under the Commitment Agreements if such breach is not
cured within the applicable cure period contained in the Commitment Agreements.

                     6.3.2  Upon receipt of a notice of default, the defaulting
party will have a period of thirty days in which to cure the default. If the 
non-defaulting party does not believe that the default has been cured during the
foregoing cure period, then the non-defaulting party may

                                       13
<PAGE>
 
terminate this Agreement immediately upon written notice to the defaulting
party.  If a defaulting party repeatedly defaults under this Agreement (as
evidence by the issuance of a notice of default by the other party two or more
times in a twelve month period), then the non-defaulting party may elect to
terminate this Agreement on thirty days advance written notice without the
defaulting party having a right to cure.  During any notice and cure period,
both parties shall continue to be bound by all the terms and conditions of this
Agreement.

                     6.3.3  The rights and remedies of the non-defaulting party
are not exclusive and are in addition to any other rights and remedies it may
have available under law or equity. Notwithstanding anything to the contrary
contained herein, the rights and obligations of the parties pursuant to Sections
1, 2.3, 4.2.2, 4.3, 4.4, 5.1, 5.2, 5.4, 5.6, 6.4, 7.3, 7.4, 7.5, 7.6 and 8 will
survive any termination or expiration of this Agreement.

              6.4   Transition Period.   Notwithstanding the expiration or
                    -----------------                                     
termination of this Agreement for any reason, at its election, Intuit may
request, and CNC shall continue to provide, the CNC Services on a non-exclusive
basis for a period of up to one year beyond such expiration or termination on
the terms and conditions in effect at that such time (the "Transition Period").
In the event of a termination or expiration of this Agreement, CNC shall
cooperate in planning and executing with Intuit (each party to bear its own
costs) a transition plan for the transfer of the Internet access services from
CNC to Intuit or Intuit's designee, and Intuit shall be entitled to use such CNC
Confidential Information as may be necessary to effect such transition.  Each
party shall take any actions or deliver any documents reasonably requested by
the other party to effect the expiration or termination of this Agreement, and
the transfer of access services.

          6.5  Force Majeure Extension.
               ----------------------- 

               6.5.1  Definitions.  For the purposes of this Section 6.5, the
                      -----------                                            
following definitions shall apply:

                      6.5.1.1  A "Force Majeure Event" shall be a delay by CNC
in its performance of, or a failure by CNC to perform pursuant to,  this
Agreement where such delay or failure is caused by an act of God, acts of civil
or military authority, fire, flood, strikes, war, epidemics or some other
unforeseeable cause beyond CNC's reasonable control and without its fault or
negligence that adversely affects the availability of services by all
telecommunications and/or Internet access services providers like CNC, such as a
major malfunction of a public telecommunications network in the Northeastern
region of the United States.

                       6.5.1.2   A "Termination Event" shall mean a circumstance
in which Intuit has given notice of default to CNC pursuant to Section 6.2 or
Section 6.3.1.1 because of CNC's failure to provide the CNC Services in
accordance with this Agreement.

                6.5.2  Extension of Cure Period.  If the primary cause of the
                       -------------------------                             
Termination Event is a Force Majeure Event, then Intuit agrees to provide CNC
with an overall cure period of sixty days from the date of Intuit's notice of
default or termination (the "Extended Cure Period") subject to CNC's
satisfaction of the following conditions: (1) CNC shall immediately notify
Intuit of any circumstances which result (or may result) in a Force Majeure
Event (in advance when the situation permits), (2) CNC shall (i) immediately
develop and implement a corrective action plan designed to promptly reestablish
the CNC and Internet Services to Intuit and the Customers, and (ii) use its best
efforts to avoid, mitigate or remove such circumstances and to reestablish the
CNC and Internet Services at its expense by providing alternate access services
to Intuit and its Customers, e.g., the establishment of toll free 800# service,
                             ----                                              
(3) CNC shall provide detailed updates upon request to Intuit of CNC's progress
in executing the corrective action plan and restoring the

                                       14
<PAGE>
 
CNC and Internet Services, and (4) CNC shall immediately continue its
performance in accordance with this Agreement  whenever such conditions are
removed.

                6.5.3  Consequences of Continuing Default.  Notwithstanding the
                       ----------------------------------                      
provisions of Section 6.5.2, Intuit may immediately terminate this Agreement in
accordance with the original time periods and procedures set forth in Section
6.2 or 6.3.1.1, as applicable, if (1) CNC fails to cure any breach or  default
within the Extended Cure Period, or (2) CNC otherwise breaches the conditions
for Intuit's grant of the Extended Cure Period, such as where CNC fails to use
its best efforts to reestablish services to Intuit and its Customers in the case
of a Force Majeure Event.

     7.   Representations, Warranties and Indemnities.
          ------------------------------------------- 

          7.1  No Conflicts.  Each party hereto represents and warrants to the
               ------------                                                   
other that the execution, delivery, and performance of this Agreement by such
party will not conflict with or result in any breach of, or constitute a default
under, any material agreement, instrument or undertaking to which it is a party
or by which any of its property is bound.

          7.2  Authority.  Each party hereto represents and warrants to the
               ---------                                                   
other that it has the power to make and carry out the terms of this Agreement
and each has taken, and will take, all actions, corporate or otherwise,
necessary or advisable to authorize the execution, delivery and performance of,
and to perform, its respective obligations under this Agreement.

          7.3  No Infringement.  CNC represents and warrants on a continuing
               ---------------                                              
basis that neither the CNC Code, nor the exercise by Intuit of any of the rights
granted under this Agreement, will infringe any intellectual property right of
any third party and that there is no litigation or claim pending or, to CNC's
knowledge, threatened relating thereto.  CNC shall and hereby does indemnify and
defend  Intuit and hold it harmless from and against any and all claims,
liabilities, losses, costs and expenses including, but not limited to,
reasonable attorneys' fees and costs of suit, incurred by Intuit as a result of
or arising from any claim or proceeding made or brought against Intuit that the
use, reproduction, marketing, sale, sublicensing or distribution of CNC Code or
use of the CNC Services, infringes any patent, copyright or other rights of any
third party, or that the CNC Code or CNC Services are defective.  This indemnity
shall not apply to the extent such claims result from Intuit's own modification
or alteration of the CNC Code.  Intuit shall promptly notify CNC of any such
claim(s) and shall, at CNC's request and expense, cooperate in the investigation
and defense of such claim(s).

          7.4  Indemnification by Intuit.  Intuit shall and hereby does
               -------------------------                               
indemnify and hold harmless CNC and its officers, directors, stockholders,
employees and any other agents from any claim, demand, liability, cost or
expense they may incur to any third party relating in any manner to the use of
the CNC Network by Intuit or its Customers (except to the extent such claims or
demands result from CNC's negligence, gross negligence or willful misconduct or
are otherwise indemnifiable by CNC pursuant to this Agreement).  CNC agrees to
give Intuit prompt notice of any claim or demand to which it becomes aware as to
which this Section may apply and to cooperate with Intuit in the defense of such
claim or demand.

          7.5  Indemnification by CNC.  CNC shall and hereby does indemnify and
               ----------------------                                          
hold harmless Intuit and its officers, directors, stockholders, employees and
any other agents from any claim, demand, liability, cost or expense they may
incur to any third party relating in any manner to the use, operation or
malfunction of the CNC Network by CNC or customers of CNC (except to the extent
such claims or demands result from Intuit's negligence, gross negligence or
willful misconduct or are otherwise indemnifiable by Intuit pursuant to Section
7.4 of this Agreement). Intuit agrees to give CNC prompt notice of any claim or
demand to which it becomes aware as to

                                       15
<PAGE>
 
which this Section may apply and to cooperate with CNC in the defense of such
claim or demand. During the Service Term, CNC shall use commercially reasonable
efforts to obtain, maintain and provide a reasonable amount of insurance against
claims covered by this indemnification provision naming Intuit as an additional
named insured and, if obtained, provide evidence of the same to Intuit.

          7.6  Limitation of Liability.  EXCEPT PURSUANT TO THEIR RESPECTIVE
               -----------------------                                      
INDEMNIFICATION OBLIGATIONS SET FORTH IN SECTIONS 7.3, 7.4 AND 7.5 ABOVE,
NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR INCIDENTAL, CONSEQUENTIAL,
INDIRECT, OR SPECIAL DAMAGES OF THE OTHER PARTY ARISING OUT OF THIS AGREEMENT.

     8.   Miscellaneous.
          ------------- 

          8.1  Notices.  Except as otherwise specified herein, all notices,
               -------                                                     
requests, demands or communications required hereunder shall be in writing and
delivered personally, or sent either by the equivalent of U.S. certified mail,
postage prepaid return receipt requested or by overnight delivery air courier
                                                                             
(e.g., Federal Express), or sent by facsimile (if such facsimile notice is
- -----                                                                     
followed immediately by a letter delivered personally or by overnight delivery
air courier), to the parties at their respective addresses set forth on the
signature page hereto.  All notices, requests, demands, or communications shall
be deemed effective immediately upon the earlier of personal delivery or
confirmed facsimile transmission, three days following deposit in the mails as
set forth above, or one day following delivery to the overnight delivery air
courier in accordance with this Section.  The parties may change their
respective points of contact, or addresses or phone or facsimile numbers for
notification from time to time on five days advance written notice pursuant to
the procedures set forth in this section.

          8.2  Entire Agreement.  This Agreement will not be effective unless
               ----------------                                              
and until the parties have fully executed and delivered this Agreement.  This
Agreement may be executed by the parties in separate counterparts, each of which
when so executed and delivered shall be an original, but all such counterprats
shall together constitute one and the same instrument.  This Agreement
constitutes the entire understanding between the parties with respect to the
provision of the CNC Services contemplated herein and supersedes all prior
agreements, written or oral, between the parties hereto with respect thereto.
The provisions of the exhibits to this Agreement are supplementary to the body
of the Agreement and shall be interpreted in such a manner; provided, however,
that in the event of an irreconcilable conflict arising between the provisions
of the exhibits and the body of this Agreement, the exhibits shall prevail.
This Agreement shall not be modified except in a writing signed by and exchanged
between both of the parties and expressly referencing this Agreement.  Any
additional or different terms in the parties communications, whether
acknowledgments, invoices or otherwise, are hereby deemed to be material
alterations and notice of objection to them and rejection of them is hereby
given.  No waiver of any provision of the Agreement or any right or obligations
of either party hereunder shall be effective, except pursuant to a writing
signed and delivered by the party waiving compliance. Any such written waiver
shall not be construed as, or constitute, a continuing waiver of such breach, or
of other breaches of the same or other provisions of this Agreement.  Neither
party shall by mere lapse of time without giving notice or taking other action
hereunder be deemed to have waived any breach by the other party of any of the
provisions of this Agreement.

          8.3  California Law.  This Agreement shall be governed by and
               --------------                                          
construed in accordance with the substantive laws of the State of California
(not including its choice of law provisions).

                                       16
<PAGE>
 
          8.4  No Assignment.  Neither party shall assign its rights or delegate
               -------------                                                    
its obligations under this Agreement without the prior written consent of the
other party hereto; provided, however, that Intuit may assign this Agreement, in
whole or in part, to any subsidiary or affiliate.  This Agreement shall be
binding on all successors and permitted assigns of the parties.

          8.5  Severability.  If any provisions of this Agreement shall be held
               ------------                                                    
by a court, arbitrator or other tribunal of competent jurisdiction to be invalid
or unenforceable, such provisions shall be deemed valid and enforced to the
maximum extent permissible and the remaining portions of this Agreement shall
remain in full force and effect.

          8.6  No Third Party Beneficiaries.  Except for permitted assigns, this
               ----------------------------                                     
Agreement does not create, and shall not be construed as creating, any rights
enforceable by any person or entity not a party to this Agreement; provided,
however, that any subsidiary or affiliate of Intuit may use the CNC Services or
offer Internet Services using the CNC Network on the terms and conditions set
forth in this Agreement.

          8.7  Construction.  The parties acknowledge and agree that the terms
               ------------                                                   
hereof reflect extensive negotiations between the parties and that this
Agreement shall not be deemed, for the purpose of construction and
interpretation, that either party drafted this Agreement.  Each party is
responsible for paying its own legal and professional fees and costs with
respect to the negotiations, execution and performance of the Agreement.  The
headings used in this Agreement are for convenience only and shall not be
considered in its interpretation.

     IN WITNESS WHEREOF, the parties have executed and delivered this Agreement
on the Execution Date and agree that is shall be effective as of the Effective
Date and it shall be deemed accepted and made in San Diego, California.

Execution Date: December 11, 1995


INTUIT INC.                                CONCENTRIC NETWORK CORPORATION


By: /s/ William Harris                     By: /s/ Henry Nothhaft
  ------------------------------              ---------------------------------
  William Harris, Executive Vice              Henry Nothhaft, President and CEO
  President

Address: 6256 Greenwich Drive               Address: 10590 N. Tantau Avenue
         San Diego, CA  92122                        Cupertino, CA 95014

                                       17
<PAGE>
 
<TABLE>
<CAPTION>
 
LIST OF EXHIBITS
- ----------------
<S>     <C>
 
A   -    CNC Network
 
B   -    Development Project Work Statement
 
C   -    CNC Network Operations and Customer Service
 
D   -    Service and Customer Charges
 
E   -    Security Guidelines
 
F   -    License Agreement
</TABLE>

                                       18
<PAGE>
 
                                  EXHIBIT "A"
                                  -----------

                                  CNC NETWORK

     A.   Current CNC Network Structure: The general description of the CNC
          -----------------------------                                    
Network is depicted in Attachment A-1 hereto and in that certain CNC Private
Placement Memorandum dated November 3, 1995 (the "PPM").  Additionally, an
identification of certain material equipments and systems comprising the CNC
Network are identified in that certain Master Lease between CNC and Racal-
Datacom, Inc., dated August 4th, 1994.  For the purposes of this Agreement, the
CNC Network shall be deemed to be the end-to-end communications and related
information systems (a) beginning at either the local number of a POP, or the
local exchange number in the case of someone using a Non-POP Access, and (B)
ending at the Intuit Systems or Intuit Areas.

     B.   Points of Presence.  A list of the current  POPs (and their associated
          ------------------                                                    
Ports) operated by CNC in the continental United States and Canada is set forth
in the PPM and in Attachment A-1 hereto, which information shall be updated and
                  --------------                                               
provided to Intuit as it changes.  Further, pursuant to the terms of this
Agreement, CNC shall do each of the following:

          1      Increase the number of Ports in the CNC Network in the
continental United States to at least [*] Ports  by January 1, 1996; provided,
that CNC shall use all commercially reasonable efforts to increase the number of
such Ports to at least [*] by January 1, 1996.

          2      Expand, improve and maintain on an ongoing basis the CNC
Network to cover the top 150 metropolitan areas in the continental United States
(determined by personal computer ownership statistics developed and published by
International Data Corporation (IDC) from time to time)  and, within each such
metropolitan area, provide "local access" (i.e., without message unit charges)
                                           ----                               
for at  least 92% of the general population.  CNC has used commercially
reasonable efforts to accomplish the foregoing expansion by the Execution Date
of the Agreement and, within ten days of the Execution Date, shall accomplish
the foregoing expansion of coverage.  In the United States, a "metropolitan
area" shall mean the metropolitan/geographic regions used by IDC in publishing
its statistics.

          3    Provide local access to the CNC Network for the Intuit Customers
in the seven largest Canadian metropolitan areas (as measured by population) by
November 1, 1995; provided, that CNC shall use all commercially reasonable
efforts to provide such local access to such Canadian metropolitan areas by
October 1, 1995. In Canada, a "metropolitan area" shall mean the geographic
areas as mutually agreed between the parties or, in the absence of an agreement,
based on Canadian government census areas.

          4    Cause the CNC Network to consistently support modem speeds up to
28,800 bps, and to be enhanced to be competitive with industry standards that
develop over time and that reflect the modem speeds used by Intuit's Customers.

     Notes:

          (1) Local access commitments made by CNC above may be provided either
via the installation of a physical POP or by use of a Virtual Local Access
("VLA") arrangement, at CNC's option.  A VLA is defined as the provision of
local dial access for a customer to gain local access to the CNC Network via a
local phone number that is call forwarded to a modem facility that is centrally
located.  The total number of modems (ports) at the central facility shall be
sized to support the aggregate of all VLAs being supported (i.e., as if each VLA
                                                            ----                
is a POP).


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                                       19
<PAGE>
 
          (2) In calculating the number of Ports serving an area, the parties
shall take into account any "Port equivalents" offered by a VLA arrangement,
                                                                            
i.e., CNC may have fewer physical Ports in a VLA arrangement then it would
- ----                                                                      
otherwise require if it deployed physical POPs to serve VLA territories.  (For
example: 50 POPs with 10 Ports each may be sufficiently served by a single
central VLA termination point of 250 Ports.)

     C.   Performance Standards.
          --------------------- 

          1    General Concept.  CNC acknowledges that Intuit requires access
               ---------------                                               
for its Customers to the Intuit Areas and Internet that is reliable and rapid,
has the ability to handle peak demands, is flexible in terms of future expansion
for geographic coverage, functional enhancements and capacity increases, and can
rapidly and accurately handle all registration, billing and customer service.
The parties have established the Performance Standards set forth in this
Agreement as a benchmark for initial operations, but CNC acknowledges and agrees
that such standards may increase in the future as customer expectations heighten
and the Internet access/services industry develops.  Therefore, during the Term,
the parties shall cooperate and act in good faith in evaluating, developing and
agreeing on such changes in the Performance Standards.

          2    Performance Standards.
               --------------------- 

            a.      Network Accessibility Performance Standard.  The CNC Network
                    ------------------------------------------                  
will exhibit an average busy rate below the following Performance Standard for
Intuit Customers attempting to access the CNC Network:
 
                    Target Performance Standard: [*]%

                    Minimum Performance Standard: [*]%

          Comments:
          -------- 

          (1) The busy rate at each POP will be determined statistically by
              comparing (A) the average hourly traffic load for each of CNC's
              three busiest hours  during a month to (B) the POP's traffic
              capacity at [*] grade-of-service using standard Erlang B traffic
              statistics for the number of active Ports at the POP.  The average
              of this data will yield that POP's average busy rate for the
              month.  By way of example, assume the average hourly traffic load
              for the 3 busiest hours for the San Francisco POP (with an average
              of 72 ports ) during June 1995 was 61.0, 58.0, and 53.5 Erlangs (#
              of hours of traffic through that POP per hour), resulting in an
              average of 57.5 Erlangs over the three busiest hours of the month.
              Using the standard Erlang B tables, a 72 port hunt-group
              supporting 57.5 Erlangs of traffic extrapolates to 0.97% which
              produces a P.01 grade of service, i.e., the POP's average busy
                                                ----                        
              rate for the month.  (sample Erlang B tables are attached hereto
              as Attachment A-2.)
                 --------------  

          (2) Then, the weighted average busy rate for the CNC Network will be
              computed across all POPs. The weighted average will be calculated
              based on the number of Ports at each POP. By way of example,
              assume the CNC Network only had 5 POPs with the following number
              of ports and average monthly busy rates as calculated in 2a(1):


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                                       20
<PAGE>
 
<TABLE>
<CAPTION>
 
POP    Ports  Avg Busy
- -----  -----  --------
<S>    <C>    <C>
1         24      .035
2         36      .015
3         48      .025
4         10      .005
5         72      .010
</TABLE>

              The weighted average busy rate for this 190 port network as a
              whole is .01763 (or 1.763%).

          (3) The weighted average busy rate calculated above will yield a
              number which will be compared to the applicable Performance
              Standard to determine whether or not CNC has met its Network
              Accessability performance goal for the month. By way of example,
              comparing the weighted average busy rate of P=.01763 to the Target
              Performance Standard of [*] reflects that CNC has performed better
              than targeted on this performance metric for the month of June.

             b.     Network Processing Capacity Performance Standards (Latency).
                    -----------------------------------------------------------
At peak periods of the day, the CNC Network latency shall meet the following
Performance Standards as measured on a monthly basis:

               Target Performance Standard: [*] milliseconds .

               Minimum Performance Standard: [*] milliseconds.

               Comments:
               -------- 


            (1) CNC will test the CNC Network for latency at least 3 days per
  week during the three busiest hours of the day as determined either a) by the
  prior month's three busiest hours EST (e.g., 10, 11, 12 PM EST) of the CNC
                                         ----                               
  Network in general, or b) by the three busiest hours of use by Intuit
  subscribers) if CNC can calculate the Intuit-specific busy hours.  Each day's
  test will include a series of 10 or more ICMP "Ping" tests containing 50 bytes
  of payload from a CNC host in either Bay City, MI or Cupertino, CA to a router
  in each of at least 50 of CNC's U.S. POP sites.  The average round-trip
  latency of each sampled POP (minimum of 10 samples per POP per test) will be
  computed. Once a month, the average, 95th, and 90th percentile of all sampled
  POP's average latencies will be computed and compared against the Performance
  Standards.

            (2) By way of example, assume the network only had 5 POP sites.  A
  sample of 10 Ping tests are run at 11PM EST on September 15th from Bay City to
  each of these 5 POPS with the following results:
<TABLE>
<CAPTION>
 
POP        Ping Samples (in milliseconds)       Average
- -----  ---------------------------------------  -------
<S>    <C>                                      <C>
1      100 120 150 200 275 150 120 120 100 090    142.5
2      085 095 100 120 110 175 300 100 090 105    128.0
3      110 145 090 100 095 080 095 100 110 105    103.0
4      200 220 250 190 275 245 255 280 200 275    239.0
5      100 090 095 105 095 100 105 100 110 105    100.5
                                                  -----
 
</TABLE>


- ----------------
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requested with respect to the omitted portions.

<PAGE>
 
<TABLE>

<S>    <C>                                      <C>
       Overall Average                            142.6
</TABLE>

          Assume a similar test was conducted on 15 other days during the month
          yielding a total of 80 sample averages.  At the end of the month, the
          average (A) and standard deviation (SD) of the 80 data samples would
          be computed. Using elementary statistics, the 95th percentile can be
          computed as "A / (1.65 x SD)", and the 90th percentile would equal "A
          / (1.25 x SD)".

          c.        Customer Service/Support Performance Standards.  Within ten
                    ----------------------------------------------             
days of its receipt of CNC's monthly usage reports, Intuit will develop and
provide to CNC a non-binding forecast of anticipated customer service volumes
                                                                             
(i.e., number of calls) for the following month. So long as actual call volumes
- -----                                                                          
are not more than [*] greater than Intuit's forecasted call volumes, the
following Performance Standards shall apply.

                         (1)  Occurrence of Busy Signals on Customer Calls
                              --------------------------------------------

          Service calls by the Customers to the CNC service center (or its
          chosen outsourcer) shall experience a busy signal no more often than
          the following Performance Standards:

            Target Performance Standard: [*] of the total calls received.

            Minimum Performance Standard: [*] of the total calls received.

                    Comments:
                    -------- 

               (a) The busy rate will be determined by a) actual busies as
          reported by the PBX delivering calls to the Intuit hunt group at CNC,
          or b) by a statistical estimate of busies based on traffic volume
          delivered to Intuit trunk group on a weighted average basis across the
          month's two busiest hours of each day (i.e., approximately 60 samples
                                                 ----                          
          per month).

          (b) CNC shall advise Intuit of its automatic call dispatch (ACD)
              system's ability to produce this information in the format
              required for analysis, provided that CNC will provide any
              additional analysis not performed by the ACD.

                         (2)  Average Speed of Answer (ASA)
                              -----------------------------

          Service calls to the CNC service center (or its outsourcer) shall,
          once answered by CNC's ACD system, experience an ASA no longer than
          the following Performance Standards:

                    Target Performance Standard: within [*] minutes

                    Minimum Performance Standard: within [*] minutes

                    Comments:
                    -------- 

               (a) First, the ASA will be computed for Intuit's trunks on a
          daily basis. Then, the ASA for each month will be computed as the
          weighted


- ----------------
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                                       22
<PAGE>
 
          average of the daily ASAs where the weighted average of the daily ASAs
          is the total number of calls offered each day compared to the total
          number of calls for the month.  By way of example, assume the
          following statistics for a given month:
<TABLE>
<CAPTION>
 
Day              Calls Offered        ASA           Calls Offered x ASA
- ----             -------------        ---           -------------------
<S>              <C>              <C>              <C>
 1               100  1.25 mins    125.0            call-mins            
 2               120  2.12 mins                     254.4                    
 3               150  1.97 mins                     295.5                    
 "                                                                            
 "                                                                            
 "                                                                            
 30              220                1.75 mins       385.0                    
                 ---                                -----                    
                 590 calls      1,059.9 call-mins/590 calls = 1.80 min ASA
                                                              ------------
</TABLE>

               If this data represented all 30 days, then the ASA for the month
     would be 1.8 minutes which would be compared against the [*] Target
     Performance Standard.

                         (3)  Customer Satisfaction Ratings
                              -----------------------------

                    Customers shall report a satisfaction with CNC's customer
               service (provided directly or indirectly) meeting or exceeding
               the following Performance Standards:

               Target Performance Standard: [*] on a scale of [*], or the
     standard set for either internal or external call centers supporting this
     service.

               Minimum Performance Standard: [*] on a scale of [*], or the
     standard set for either internal or external call centers supporting this
     service.

                    Comments:
                    -------- 

                    (a) Intuit and CNC shall jointly develop and agree on a
                        customer satisfaction survey and survey methodology, and
                        update it as required during the Term of the Agreement
                        to reflect changes in customer expectations and the
                        market for Internet Services.

                    (b) The survey will be conducted periodically (but no less
                        often than monthly), as jointly agreed between CNC and
                        Intuit.

                    (c) Intuit will bear the cost of developing and
                        administering the survey. If Intuit fails to administer
                        the survey in any given month, CNC shall be assumed to
                        have satisfied the Target Performance Standard for that
                        month.

     D.   Corrective Action and Financial Penalties.  If CNC fails to satisfy
          -----------------------------------------                          
the Performance Standards set forth in Section C (above), then it shall take the
corrective actions and be subject to the financial penalties described below.
However, the corrective actions and financial penalties described in this
Exhibit "A" are in addition to, and not in limitation of, any other rights that
Intuit has

                                      23

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<PAGE>
 
pursuant to the Agreement including, but not limited to its termination rights
pursuant to Section 6 of the Agreement.

            1  Corrective Action.  If CNC's actual performance in any given
               -----------------                                           
month falls below the  Target Performance Standard for any of the aforementioned
performance standards, then CNC will use its best efforts to enhance and improve
the CNC Network and its operations so as to reasonably assure that the Target
Performance Standard will be met in the next following and subsequent months.
Such corrective action, by way of example and not of limitation, could include
CNC making available 800# access numbers to Customers who are experiencing
excessive busies when accessing local POPs or adding additional incoming lines
for Customers who are experiencing excessive busies on customer service calls.

            2  Financial Penalty.
               ----------------- 

                  a.  Background.  The parties acknowledge that problems will
                      ----------                                             
occur in the start-up of the CNC and Internet Services in projecting customer
requirements and in adjusting to differences in actual versus forecasted usage
levels.  The assessment of immediate financial penalties to CNC may not serve
either party's best interests because of the potential adverse effect on the
ability of CNC to improve the CNC Services in the short term.  Additionally, the
parties' desire to implement a mechanism to ensure that CNC is motivated to
devote the effort required to correct deficiencies in its actual versus targeted
performance, but not to inhibit a motivated CNC from achieving the Performance
Standards.  Therefore, the parties will develop mutually satisfactory
forecasting, tracking, reporting and review mechanisms consistent with the
procedures set forth in Section b. below during the initial months of the
Agreement.  By May 1, 1996, the parties shall also agree on a methodology to set
and assess financial penalties for CNC's failure to achieve the Performance
Standards.  The structure to assess such financial penalties against CNC will
include the consideration of the following factors:  (i) CNC's past and current
performance, (ii) the rate of progress CNC has/is making toward achievement of
the Target Performance Standards, (iii) the impact of missed targets on the
Customers and Intuit, (iv) the root causes of CNC's performance deficiencies,
and (v) the willingness, motivation and attitude of CNC in promptly remedying
any performance deficiencies.

                  b.  Review Process.
                      -------------- 

                          (1)  CNC and Intuit will conduct a joint Operations
Review of the CNC Network and CNC Services on a monthly basis during the first
six months of the First Contract Year (the "Implementation Phase") at a mutually
agreed location.  At this Operations Review, CNC will present Intuit with the
status of the CNC Network, Performance Standards and Customer Service
performance for the prior month, a trend line showing the history of each
Performance Standard, an analysis of the root cause of any Performance Standard
that fell below the Target Performance Standard and an action plan for
correction of any such deficiency.  These Operations Reviews are intended to be
a joint learning session whereby the parties can continuously improve the
quality of the overall CNC Services and Internet Services.

                           (2) Intuit may, at its option, request CNC to alter
its action plan for the correction of deficiencies if, in Intuit's judgment, the
proposed action plan is insufficient to correct the deficiency in a timely
manner.

                           (3) During the Implementation Phase, CNC and Intuit
shall cooperate and work diligently in  performing their respective
responsibilities under the Agreement, including the correction of  problems
causing CNC to fail to satisfy the Performance Standards and addressing
excessive or unacceptable levels of Customer complaints.  If CNC does not
correct or,

                                       24
<PAGE>
 
in Intuit's good faith judgment, make sufficient progress to correct such
performance deficiencies or resolve such customer complaints despite the
parties' cooperation, then Intuit may terminate the Agreement, in addition to
exercising any of its rights provided in the Agreement.  In such event, CNC
agrees to assist Intuit in transitioning the CNC Services to Intuit or its
designee consistent with the transition procedures set forth in the Agreement.
During the first four months following the commencement of the Transition
Period, Intuit's payments to CNC for Service Charges shall be reduced to [*]  
per hour for all Customers/Service Categories.  If the transition is not
completed by Intuit within the first four months of the Transition Period, then
the Service Charges will revert to the levels specified in Exhibit D until the
transition is completed.  If Intuit chooses to terminate the Agreement, then CNC
will promptly deliver to Intuit the source code for all Intuit registration
server software (except to the extent such source code is owned by third parties
and cannot be delivered by CNC, as may be the case with certain software
development tools) at no cost to Intuit and otherwise perform its obligations
set forth in the Agreement.

                         (4)  By the end of the Implementation Phase, Intuit and
CNC will jointly agree to continue the Operations Reviews as outlined above, or
agree on some other mutually acceptable review and improvement process.

                         (5)  By the end of the Implementation Phase, Intuit and
CNC will jointly agree on (i) a process for determining what and how financial
penalties will be assessed by Intuit against CNC for CNC's failure to achieve
the Performance Standards, and (ii) the amount of the penalty. Any financial
penalties assessed by Intuit against CNC will be made only after a penalty
review conference attended by senior managers of both CNC and Intuit and the
setting of such penalties shall give due consideration to the factors described
above. CNC will not be subject to financial penalties for failure to meet
Performance Standards in any month that the actual CNC Network usage or customer
service call volume relating to Intuit Customers exceeds Intuit's initial
forecast for such month by more than [*]. For example, if Intuit's December 1995
forecast for January, February and March estimates that March 1996 CNC Network
usage will be [*] hours and the actual CNC Network usage by the Customers is [*]
hours, then CNC will not be subject to financial penalties based on its failure
to achieve the applicable Performance Standards for March.

     5.   Significant Service Interruptions.  In addition to its rights to
          ---------------------------------                               
terminate the Agreement pursuant to Section 6, Intuit may immediately give
notice of termination of the Agreement if either of the following Service
Interruptions occur, subject only to CNC's rights relating to a Force Majeure
Event pursuant to Section 6.5 (if applicable):

            1  A "Network Availability Service Interruption" which shall mean a
service interruption whereby the CNC Network is available for less than ten
hours during any given 48 hour period to more than [*] of the Customers.

            2  A "Customer Support Service Interruption" which shall mean a
service interruption whereby customer service or support is available for less
than ten hours during any given 96 hour period to more than [*] of the
Customers.


Attachments:
- ----------- 

A-1: Network Description (3 pages); List of current CNC POPs and related Ports
(5 pages)

A-2: Sample Erlang B Table (2 pages)

                                       25

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    [*] Certain information on this page has been omitted and filed separately 
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<PAGE>
 
                                  EXHIBIT "B"
                                  -----------

                       DEVELOPMENT PROJECT WORK STATEMENT

1.   Project Coordination
     --------------------
 
     Project Managers:
     ---------------- 
 
     Intuit:   Jennifer Jones-Hall

     CNC: John Peters

     The Project Manager of each party shall be responsible for arranging all
     meetings, visits and consultations between the parties that are of a non-
     technical nature.  They shall also be responsible for receiving all notices
     under this Agreement and for all administrative matters such as invoicing
     and payments.  All amendments to the Agreement must be signed by an officer
     of the respective party.

     Technical Coordinators:
     ---------------------- 

     Intuit: Kim MacPherson

     CNC: Mike Sharmon

     The Technical Coordinator of each party shall be responsible for technical
     and system performance matters, and the transmission and receipt of
     deliverables and technical information between the parties.

     The designation of a party's Project Manager or Technical Coordinator may
     be changed from time to time by written notice to the other party.

2.   Project Description.  The parties will perform the activities associated
     -------------------                                                     
with hardware, software and systems development related to the actions generally
described and on the timetable set forth in "Production Schedules" developed by
Intuit based, in part, on supporting production schedules developed and provided
to Intuit by CNC, an example of which is attached hereto as Attachment B-1. The
                                                            --------------     
Production Schedule shall be modified and updated by the parties as requirements
change.  Each party is responsible for providing the number of trained
personnel, facilities and other resources necessary to support the deliverable
deadlines.  Each party will be responsible for its own expenses associated with
its performance.  Because of the short deadlines associated with the initial
Development Project, the parties will work diligently and in good faith to
develop on a continuing basis  all necessary functional and technical
specifications of devices, software code and other deliverables, including any
specific enhancements that may be sought. Each party will cooperate in
developing, performing and/or delivering any reports, reviews, inspections, and
tests to be conducted.

3.   Beta Testing Procedures.  The description of and schedule for Beta testing
     -----------------------                                                   
of the System and its components shall be described in "Test Schedules"
developed by Intuit based, in part, on supporting production schedules developed
and delivered to Intuit by CNC .  Test Schedules shall be modified and updated
as requirements change.  On an ongoing basis, the parties shall review, inspect
and test the deliverables and the performance of the System (including the CNC
Network, e.g., internal quality assurance testing of CNC components such as
         ----                                                              
registration server, billing and account management systems, reconciliation
process, security, etc.) in order to determine whether
                   ---                                

                                       27
<PAGE>
 
such comply with the specifications and performance standards therefor. To the
extent that any deliverables fail beta testing, the parties shall use their
reasonable best efforts to correct any problems or defects, which  corrections
shall not be deemed completed until the parties  determine in good faith that
such meet all applicable specifications and performance standards.  Each party
will be responsible for its own expenses associated with its performance.

4.   Ongoing System Development.  CNC acknowledges that the Internet Services
     --------------------------                                              
offered by Intuit will be developed, modified and enhanced during the Term of
the Agreement as, for example, when any supplier of Intuit's Internet browser
software revises its software.  Therefore, consistent with its other obligations
pursuant to the Agreement, CNC shall work with Intuit and Intuit's other
suppliers or consultants to improve, modify or take other actions necessary or
reasonable to support the Internet Services over the Term of the Agreement.
Among other things, this support may involve subsequent development projects,
beta testing and service or product introductions on the following terms:

     a.   CNC will agree to pass-through [*] any network/system
improvements made available to customers at large.

     b.   CNC will agree to maintain/fix-bugs in the existing Intuit
registration server and "free" account login/screening servers for the First
Contract Year of the Agreement [*]. CNC maintenance for the Second and Third
Contract Years will be offered on a T&M basis at the rates indicated below

     c.   New feature development (including the registration server) requested
by Intuit will be provided at the rate of [*] per staff-month or [*] for
the First Contract Year, increased by no more than [*]/year for the Second and
Third Contract Years of the Agreement.  These charges will become effective as
of the Execution Date of this Agreement (i.e., CNC will eat the development
costs-to-date on the registration/login servers).

     d.   If CNC and Intuit can not agree on the price, schedule or scope of the
new feature development for the registration server software, then Intuit may
purchase a non-exclusive source code license of the software for [*] and request
CNC to provide facilities management of an Intuit-owned server for a fee of [*]
per server. CNC will provide, at Intuit's request, up to two engineering staff
weeks of time at [*] to assist in the transition of the source code to Intuit's
engineers. It is understood that the source code and any accompanying
documentation is being delivered "as is" on the date of requested delivery.

     e.   CNC agrees to implement the Netscape "Cookie" functionality at no
additional charge in a mutually agreeable timeframe (target date is December 1,
1995).

     (f) CNC will advise Intuit in advance if CNC believes that development or
support services requested by Intuit are chargeable to Intuit.

Attachments:
- ----------- 

B-1  - Example of Production Schedule


                                       28

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<PAGE>
 
                                  EXHIBIT "C"
                                  -----------

                  CNC NETWORK OPERATIONS AND CUSTOMER SERVICE


1.   Network Operation.  CNC is responsible for all ongoing on-line network and
     -----------------                                                         
related operations such as customer logon procedures, registration, customer
database management, isolation of Customer Information from other data,
procedures regarding access/services upgrades, system maintenance, network
monitoring, surveillance, capacity planning, failure and contingency procedures,
etc.
- --- 

2.   Customer Service.  Intuit's goal is to provide exceptional customer support
     ----------------                                                           
with respect to the Internet Services.  The parties acknowledge that the
customer support model initially implemented may change over time as they better
understand the customers' needs and problem areas.  Initially, customer support
will be categorized into the following areas:

               Category #       Description of Customer Support
               ----------       -------------------------------

                    1       Customer support relating to Intuit software
                            applications, e.g., Quicken, Quickbooks, TurboTax,
                                          ----
                            etc.
                            --- 

                    2       Customer support prior to registration, i.e.,
                                                                    ---- 
                            "getting started" help (such as browser install,
                            network configuration and modem setup)

                    3       Registration support (on-line connection to
                            registration server for Restricted and Full Internet
                            Access)

                    4       Network connection support (i.e., cannot establish
                                                        ----                  
                            connection, routine network trouble calls, busies,
                            etc.)
                            ---  

                    5       Full Internet Access Support (7 days/week by 24
                            hours/day)

   Initially, Intuit will provide customer support in Categories 1 and 2 at its
expense, and CNC shall provide customer support in Categories 3, 4 and 5 at its
expense.  CNC is authorized, with Intuit's prior written consent, to subcontract
technical support to a qualified third party. Subsequently, Intuit (or its
subcontractor), at its election, may assume responsibility for customer support
in Category 3.  In such event, CNC shall be responsible for paying Intuit the
cost of all customer support provided by Intuit in Category 3 at a rate agreed
to between the parties based on prevailing outsourcer rates (or, if no agreement
is reached, at the rate of [*]/minute per phone call).  Additionally, if
Intuit receives customer service calls in Categories 3, 4 or 5 because of CNC's
inability to service the level of customer calls being received or because
malfunctions on the CNC Network are causing increased customer problems, then
CNC shall, as a part of the Monthly Reconciliation Process described in Exhibit
                                                                        -------
"D" to the Agreement, reimburse Intuit at a rate agreed to between the parties
- ---                                                                           
based on prevailing outsourcer rates (or, if no agreement is reached, at the
rate of [*]/minute per call).  Conversely, Intuit shall be responsible for
paying CNC the cost of all customer support provided by CNC in Categories 1 or 2
at the rate of [*] per call.


                                       29

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<PAGE>
 
   Intuit and CNC will jointly develop call answering, call transfer and other
customer service related procedures, e.g., use of Intuit brand names.  In this
                                     ----                                     
regard, CNC will provide technical support training at its expense to Intuit's
call centers (whether call services are performed by Intuit or subcontracted).

3. Customer Support Managers.
   ------------------------- 

   Intuit:          Jim Bishop

   CNC:             Eileen Curtis

   The Customer Support Manager of each party shall be responsible for arranging
all meetings, visits and consultations between the parties relating to customer
service including forecast reviews, satisfaction of performance standards
relating to customer service and support, implementation plans, escalation
procedures for problems, call flows, call categories, and similar matters
affecting customer support and service.  The designation of a party's Customer
Support Manager may be changed from time to time by written notice to the other
party.

4. Customer Billings and Credits.
   ----------------------------- 

   A. Background.  The parties acknowledge that additional operating experience 
      ----------                                          
with the Internet Services and Customer feedback is required in order to fully
develop effective billing and credit procedures. Therefore, during the period
prior to February 1, 1996, Intuit and CNC will define, develop and implement
customer billing and credit procedures. The following sections identify the
initial procedures prior to February 1, 1996.

   B. Customer Billing Procedures.  During the initial phase of operations, the 
      ---------------------------                              
parties will handle Customer billings as follows:

      1. When a Customer upgrades from Restricted Internet Service to Full
Internet Service (or such other levels or types of services established in the
future), CNC will promptly conduct a billing account validation pursuant to
customary industry procedures, e.g., confirmation of the card number and
                               ----
expiration date. If the Customer satisfactorily completes the billing account
validation process, then CNC will register the Customer for Full Internet
Service (or such other levels or types of services established in the future)
and store this information in the appropriate data files (an "Upgrade Account").
CNC and Intuit will develop mutually acceptable procedures to refine the billing
account validation process, such as determining the number of times that a
Customer may attempt to upgrade before being denied upgrade because of
validation problems.

      2. Shortly after midnight every night, CNC will transfer the Upgrade
Accounts to the appropriate data files and run Customer billings. Customers
shall be billed monthly on their anniversary date in advance for any service
plan-related charges (e.g., where Customers have taken a package billing
                      ----
approach such as seven hours for $9.95), and in arrears for any charges relating
to usage in excess of service plan amounts or where the Customer has elected to
be billed on an hourly basis. The monthly billing information shall be
transmitted to the credit card processor designated by Intuit (the "Processor").
In selecting any Processors, Intuit shall in good faith consider CNC's
recommendations and observations, e.g., the difficulty of working with such 
                                  ----                   
Processor, the requirement for CNC to establish new procedures or systems, and
the economic effect on CNC of such changes.

      3. All Customer Charges processed by the Processor shall be deposited into
an Intuit account, and shall be Intuit's sole property.


                                       30
<PAGE>
 
   C.  Customer Credit Procedures.  During the initial phase of operations, the 
       --------------------------                              
parties will handle Customer credits as follows:

        1. Improper or Inaccurate Billings.  If CNC determines that it has 
           -------------------------------                    
improperly or inaccurately charged a Customer's credit card for Internet
Services that were not provided to or used by the Customer, then CNC shall file
and process appropriate credits for the Customer with the Processor to correct
the error. If the improper or inaccurate billing also resulted in inaccurate or
improper Service Charges being assessed to Intuit, then CNC shall provide Intuit
with appropriate credits to its Service Charges as a part of the next Monthly
Reconciliation performed pursuant to Exhibit "D."

        2. Fraudulent Billings.  If a Customer contacts CNC to request a credit 
           -------------------                                
because the Customer claims that his/her credit card was stolen or fraudulently
used, then CNC shall refer the Customer to his/her credit card company for
appropriate handling of the matter.

         3. Discretionary Usage Credits.  Intuit and CNC acknowledge that the 
            ---------------------------                 
long-term economic success of the Internet Services is affected substantially by
Customers' ongoing use of the Internet Services. Therefore, CNC may exercise its
reasonable judgment and grant usage credits to Customers where it believes such
action is in the best interests of Intuit. By way of example, if a Customer
expresses surprise at receiving a large bill but acknowledges that he or she
actually used that amount of time, then CNC might elect to give the Customer a
partial usage credit (i.e., a dollar amount equivalent to a reasonable number 
                      ----                 
of "free" hours of use on his or her next bill). Intuit, with CNC's assistance,
shall establish guidelines on granting such credits from time to time. CNC shall
not grant usage credits in contravention of such guidelines without Intuit's
written consent. In its monthly reports to Intuit, CNC shall report its grant of
such usage credits.

         5. Bad Debts. Initially, upon notification that a Customer's credit 
            ---------                                     
charges will not be paid or have been denied, CNC will take steps to have a
notification of such sent to the affected Customer the next time he/she logs on
to the CNC Network that advises the Customer to contact CNC to resolve the
credit problem and to obtain payment. During the Term, CNC and Intuit will work
together to develop and implement bad debt procedures as the need arises.


                                       31
<PAGE>
 
                                  EXHIBIT "D"
                                  -----------

                          SERVICE AND CUSTOMER CHARGES

A. SERVICE CHARGES.

   1.               Service Charges.  The Service Charges during the First
                    ---------------                                       
Contract Year payable to CNC for the CNC Services (subject to any adjustments
pursuant to the Agreement) shall be as follows:




   Amount                     Customer/Service Category
   ------                     -------------------------



                                      [*]



2.   Monthly Reconciliation Process.  Within 3 business days of the end of each
     ------------------------------                                            
calendar month, CNC shall conduct a "Monthly Reconciliation" as follows:

     a. Prepare and deliver to Intuit a report containing (A) the usage,
        customer service and performance information described in Exhibit "A",
        and (B) the "Cumulative Service Charges" chargeable to Intuit for the
        applicable calendar month, net of all applicable penalties, credits and
        reimbursements calculated as follows: (i) the chargeable time and
        related cumulative Service Charges for each Customer/Service Category
        (Full, Restricted, Non-Internet Traffic, and Off Peak Access) plus (ii)
                                                                      ----
        the amount of any Forecast Shortfall Penalty (calculated pursuant to
        Item (1) below), if any, minus (iii) financial penalties for CNC's
        failure to meet Performance Standards (see Item (2) below), if any, plus
                                                                            ----
        (iv) any amounts owed to Intuit for Customer Service Charges


                                       32

- ----------------
    [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission.  Confidential treatment has been 
requested with respect to the omitted portions.
<PAGE>
 
        reimbursable by CNC pursuant to Exhibit "C" of the Agreement, minus (v)
                                                                   -----        
        any amounts owed by Intuit to CNC for Customer Service charges
        reimbursable by Intuit pursuant to Exhibit "C" of the Agreement, plus or
                                                                         -------
        minus (vi) any other adjustments agreed to between the parties. CNC
        -----
        shall also include an invoice for the Cumulative Service Charges, as
        adjusted pursuant to this Agreement, and Intuit shall pay such invoice
        within thirty days of its receipt.

        (1)  Forecast Shortfall Penalty.  Within ten days of its receipt of
             --------------------------                                    
             CNC's Monthly Reconciliation, Intuit will develop and provide to
             CNC a non-binding rolling forecast of anticipated CNC Network usage
             by the Customers for the next three calendar months. To the extent
             that the actual volume of forecasted hours of a given month is less
             than [*] of Intuit's most recent estimate of forecasted hours for
             such month, Intuit will pay CNC the difference between the actual
             volume and [*] of the most recent estimate for such month using the
             then effective Restricted Internet Services hourly charge. By way
             of illustration, if Intuit's most recent forecast in December,
             1995, estimates an aggregate total Customer usage for January, 1996
             of [*] hours and the actual usage for January was [*] hours, then
             Intuit would be required to compensate CNC at the foregoing rate
             for the difference between [*] hours and [*] hours (i.e., [*] of
             the most recent estimate of [*] hours).

        (2)  CNC Performance Financial Penalty.  This credit will be an amount
             ---------------------------------                                
             equal to the financial penalties payable by CNC to Intuit
             established pursuant to Exhibit "A" of the Agreement.

     b. Prepare and deliver (or make available for Intuit's ready on-line
        access) to Intuit a Customer Charge report reflecting the number of
        connect hours for each Customer, the amount of Customer Charges billed
        to Customers, the amount of payments billed to and received from
        Customers, the amount of any credits given to Customers, and other
        related billing or financial information reasonably requested by Intuit.
        Additionally, CNC will deliver or make available on-line to Intuit a
        report showing all charges to and collections from Customers on a
        cumulative basis ("Monthly Customer Collections") including names,
        billing numbers, Internet name, anniversary date, time used per billing
        period and connection, payment plan, e-mail preference, pay type, and
        other information reasonably requested by Intuit.

3.   CNC Termination Right.  If the average hourly usage of the Full Internet
     ---------------------                                                   
Services Customers is less than five hours per month at the end of the
Implementation Phase, then CNC may request Intuit to enter into an arrangement
to compensate CNC for the difference between the actual average usage of such
Full Internet Services Customers and CNC's desired usage for such Customer of at
least five hours per month.  If Intuit declines to enter into such an
arrangement, then CNC may elect to terminate the Agreement effective after the
next major revision and release date for all of the Products covered by the
Agreement subject to CNC's obligation to assist Intuit in transitioning to a new
Internet access services provider pursuant to this Agreement.

B.   CUSTOMER CHARGES AND INFORMATION STATEMENTS

     Intuit will establish the Customer Charges from time to time in its sole
discretion.  As a part of the CNC Services, CNC shall deliver or make available
by December 31, 1995 usage, account and billing information on a continuous
basis to Intuit and all Customers (whether for Restricted or Full Internet
Services) through on-line access such as hours/month usage, charges/credits, and
other information reasonably requested by Intuit (the "Information Statement").
Additionally, upon


                                       33

- ----------------
    [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission.  Confidential treatment has been 
requested with respect to the omitted portions.
<PAGE>
 
Customer request, CNC shall mail a hard copy of the Information Statement to
such Customer. Prior to December 31, 1995, Customers may call CNC to obtain
their billing and account status.

C.   CNC REPORTING

     1.   Initial Reporting.  During the period prior to January 1, 1996, CNC
          -----------------                                                  
and Intuit will define, develop and implement reporting requirements.  During
this initial period, CNC will use its reasonable best efforts to provide Intuit
with requested information, but Intuit acknowledges that CNC's initial reporting
will be minimal.

     2.   Ongoing Reporting.  Not later than January 1, 1996, CNC will implement
          -----------------                                                     
the report set agreed to between the parties on a monthly basis including
information such as:
<TABLE>
<CAPTION>

<S>                                  <C>           <C>
New Subscribers/month (Actual)         -            Restricted Access, Full Access accounts
                                                   with price option 1, and Full Access account
                                                   with price option 2
Total # Base Subscribers/month         -           (same breakdown as above)
    (including New)
Average Personal Usage/month           -           (same breakdown as above)
Peak hours/day                         -           Number of subscribers (same breakdown),
                                                   number of hours                    
Peak day/week                          -           (same breakdown as "per day" report)
Number of inactive accounts            -           not used in a month per Customer/Service
                                       -           category
Customer Service Calls                 -           (breakdown to be developed)
</TABLE>                                

D.   INTUIT FORECASTING                 
                                       
     1.   Initial Forecasting.  During January 1, 1996, CNC and Intuit will 
          -------------------                                                  
define, develop and implement forecasting requirements. During this initial
period, Intuit will use its reasonable best efforts to provide CNC with
requested information, but CNC acknowledges that Intuit's initial reporting will
be minimal.

     2.   Ongoing Forecasting.  Not later than January 1, 1996, Intuit will
          -------------------                                              
implement the forecasting set agreed to between the parties including
information such as:
<TABLE>
<CAPTION>
 
<S>                                  <C>           <C>
Estimated New Subscribers/month       -            Restricted Access, Full Access accounts
Estimated Total # Base                -            (same breakdown as above)
 Subscribers/month
Estimated Average Personal            -            (same breakdown as above)
 Usage/month
</TABLE>

Intuit's forecast shall be a rolling 90 day forecast updated on a monthly basis.
For example, in December 1995, Intuit will make its forecast for the immediately
following January, February and March 1996.  Then, in  January 1996, Intuit will
issue an updated  forecast for the immediately following February and March, and
makes its initial forecast for April. As noted in Section D.2.(b)(5) of Exhibit
"A", CNC shall not be held responsible for failing to achieve those Performance
Standards adversely affected by a situation where Intuit's initial [*] forecast
for a month underestimates actual network usage or customer service calls by
more than [*]; provided, however, that CNC will use its reasonable best efforts
to adjust to changes in Intuit's forecasts and the actual volumes experienced at
any given time so as to attempt to achieve such Performance Standards.


                                       34

- ----------------
    [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission.  Confidential treatment has been 
requested with respect to the omitted portions.
<PAGE>
 
                                  EXHIBIT "E"
                                  -----------

                              SECURITY GUIDELINES


CNC acknowledges that the security of Customer Information is an absolute
requirement.  During the Implementation Phase, the parties will develop all
necessary or advisable systems, practices, guidelines and procedures to achieve
this requirement, and continue to do so during the Term of the Agreement.




                                       35
<PAGE>
 
                                  EXHIBIT "F"
                                  -----------

                               LICENSE AGREEMENT

     THIS LICENSE AGREEMENT ("Agreement")  is effective as of August 1, 1995
(the "Effective Date"), by and between Intuit Inc., a Delaware corporation
("Intuit"), and Concentric Network Corporation, a Florida corporation formerly
known as Concentric Research Corporation ("CNC"), with reference to the
following facts:

                                    RECITALS
                                    --------

     A.   CNC and Intuit have entered into that certain Internet Access Services
Agreement effective as of August 1, 1995 (the "Access Agreement") pursuant to
which CNC has agreed to license the use of the CNC Code to Intuit.

     NOW, THEREFORE, for valuable consideration, receipt of which is hereby
acknowledged, the parties hereto agree as follows:

1.   Definitions.  "CNC Code" shall mean the POP, login server, registration
     -----------                                                            
server, encryption, data security and other software described in or relating to
the performance of  the Access Agreement, including any related documentation,
developed during the Term of the Access Agreement.  Any other capitalized terms
not defined herein shall have the meaning given them in the Access Agreement.

2.   Grant of License.
     ---------------- 

     2.1  CNC hereby grants to Intuit (or its designee, e.g., a replacement
Internet access service provider) a world-wide, non-exclusive, fully paid,
perpetual right and license (i) to use all or any portion of the CNC Code in
connection with the production, copying, license, distribution and sale of the
Products, including any portion of the CNC Code which may be distributed or made
available to the Customers in order for them to properly access the CNC Network,
and (ii) to sublicense the copying and use of the CNC Code to the Customers in
connection with the Customers' use of the Products, provided that Intuit's right
to distribute the CNC Code to its Customers shall extend only during the Term
and Transition Period.  However, nothing in this Agreement or the Access
Agreement shall affect the continuing right (i) of Intuit to distribute Product
containing the CNC Code that may be in the process of manufacture or held in
inventory at the time that the Term of the Access Agreement terminates or
expires, or (ii) of the Customers to use the CNC Code that is contained in any
Product that they may acquire.

     2.2  The grant to Intuit in Section 2.1 includes the right to use, modify,
adapt, copy, display and otherwise exploit the CNC Code in any manner reasonably
necessary or advisable for Intuit (or its designee) to provide Internet services
or access to the Customers during or after the Term of the Access Agreement.

     2.3  CNC and Intuit intend that the license granted to Intuit pursuant to
this Agreement shall ensure (A) that Intuit is able (i)  to smoothly, quickly,
cost-effectively and efficiently transition the CNC Services from CNC to another
access services provider and (ii) to provide high quality services at the
performance levels specified in the Access Agreement to the Customers on a
continuous basis in the event of such a transition, and (B) that the Customers
are able to use the Internet Services during, from and after such a transition.
However, the definition of the CNC Code and the scope and the duration of the
license and rights granted in this Agreement are not intended to extend beyond
the definition, scope and duration, as applicable, that Intuit reasonably
determines in good faith to be necessary or advisable to accomplish the
intention of the parties as expressed in the foregoing sentence or in the Access
Agreement.


                                       36
<PAGE>
 
3.   No Infringement.  CNC represents and warrants on a continuing basis that
     ---------------                                                         
neither the CNC Code, nor the exercise by Intuit of any of the rights granted
under this Agreement, will infringe any intellectual property right of any third
party and that there is no litigation or claim pending or, to CNC's knowledge,
threatened relating thereto.  CNC shall and hereby does indemnify and defend
Intuit and hold it harmless from and against any and all claims, liabilities,
losses, costs and expenses including, but not limited to, reasonable attorneys'
fees and costs of suit, incurred by Intuit as a result of or arising from any
claim or proceeding made or brought against Intuit that the use, reproduction,
marketing, sale, sublicensing or distribution of CNC Code infringes any patent,
copyright or other rights of any third party, or that the CNC Code is defective.
This indemnity shall not apply to the extent such claims result from Intuit's
own modification or alteration of the CNC Code.  Intuit shall promptly notify
CNC of any such claim(s) of which it becomes aware and shall, at CNC's request
and expense, cooperate in the investigation and defense of such claim(s).

4.   Miscellaneous.
     ------------- 

     4.1  Entire Agreement.  This Agreement shall be governed by and construed
          ----------------                                                    
in accordance with the substantive laws of the State of California (not
including its choice of law provisions). This Agreement, as supplemented by the
Access Agreement, constitutes the entire understanding between the parties with
respect to the licensing of the CNC Code contemplated herein.  This Agreement
shall not be modified except in a writing signed by and exchanged between both
of the parties and expressly referencing this Agreement.  No waiver of any
provision of the Agreement or any right or obligations of either party hereunder
shall be effective, except pursuant to a writing signed and delivered by the
party waiving compliance. Any such written waiver shall not be construed as, or
constitute, a continuing waiver of such breach, or of other breaches of the same
or other provisions of this Agreement.  Neither party shall by mere lapse of
time without giving notice or taking other action hereunder be deemed to have
waived any breach by the other party of any of the provisions of this Agreement.
This Agreement shall be binding on all successors and assigns of the parties.

     4.2  No Executory Obligation.  CNC acknowledges that this Agreement is not
          -----------------------                                              
an "executory contract" within the meaning of the U.S. Bankruptcy Code and shall
not be subject to rejection by any debtor-in-possession, bankruptcy trustee or
the like.

     4.3  Severability.  If any provisions of this Agreement shall be held by a
          ------------                                                         
court, arbitrator or other tribunal of competent jurisdiction to be invalid or
unenforceable, such provisions shall be deemed valid and enforced to the maximum
extent permissible and the remaining portions of this Agreement shall remain in
full force and effect.

     IN WITNESS WHEREOF, this Agreement shall be effective as of the Effective
Date and it shall be deemed accepted and made in San Diego, California.


Execution Date: December 11, 1995

INTUIT INC.                            CONCENTRIC NETWORK                
                                       CORPORATION                              
                                                                                
                                                                                
By: /s/ William Harris                 By: /s/ Henry Nothhaft
   -------------------------             ----------------------------------
   William Harris, Executive              Henry Nothhaft, President and CEO
       Vice President                                                           
                                                                                
Address: 6256 Greenwich Drive          Address: 10590 N. Tantau Avenue          
         San Diego, CA  92122                   Cupertino, CA 95014       


                                                                           
                                       37
<PAGE>
 
                                                                   
                              AMENDMENT NO. 1 TO
                       INTERNET ACCESS SERVICES AGREEMENT

THIS AMENDMENT NO. 1 TO INTERNET ACCESS SERVICES AGREEMENT ("Amendment") is made
and effective as of August 15, 1996 (the "Effective Date"), by and between
Intuit Inc., a Delaware corporation ("Intuit"), and Concentric Network
Corporation, a Florida corporation ("CNC"), with reference to the following
facts:

                                    RECITALS
                                    --------

     A.   Intuit and CNC are parties to that certain Internet Access Services
Agreement effective as of August 1,1995 (the "Agreement").

     B.   Intuit and CNC desire to expand the types of pricing plans available
to the Customers and, hereby, agree to amend the Agreement as set forth herein.

     NOW, THEREFORE, for valuable consideration, the parties hereto agree as
follows:

     1.   Except as otherwise defined herein, capitalized terms shall have the
meaning given them in the Agreement.

     2.   Exhibit "D" entitled "SERVICE AND CUSTOMER CHARGES" is hereby revised
and restated in its entirety as follows:

"A.  SERVICE CHARGES.

     1.   Service Charges. Intuit may, at its discretion, offer pricing plans to
          ---------------                                                       
the Customers of various types. As of the date of this Amendment, Intuit intends
to offer plans in the following general categories.

          a.   Standard Plans.
               -------------- 

               (1) "Standard Plans" are arrangements whereby Customers are
charged on an hourly basis, or charged a specified dollar amount for a certain
number of hours of "free" usage per month with monthly usage in excess of the
free amount chargeable at a specified hourly rate, and CNC is compensated on a
hours usage basis. An example of this type of plan is Intuit's current "Frequent
User Plan" under which the Customer receives seven hours of usage for $9.95 per
month, and pays $1.95 for each hour of usage in excess of seven hours in the
specified month. The Service Charges during the First Contract Year payable to
CNC for the CNC Services (subject to any adjustments pursuant to the Agreement)
under Standard Plans shall be as follows:

          Amount                         Customer/Service Category
          ------                         -------------------------

          [*]                            Full Internet Services Customers

          [*]                            Restricted Internet Services Customers


- ------------------
   [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

<PAGE>
 
          *                              Non-Internet Traffic

          [*]                            "Off-Peak Access" (from 2:00 a.m. to
                                         6:00 a.m. local time, where local is 
                                         the respective time zone of the 
                                         Customer)

     *    CNC agrees to provide Intuit the most favored pricing on future Non-
          Internet Traffic based on equivalent services offered, terms and
          conditions of such offering.

     Service Charges for Standard Plans will be calculated pro rata on a one
second incremental basis (rounded to four decimal places). For example, Intuit
would be charged unadjusted total Service Charges of [*] in a Monthly
Reconciliation Report (see below) reflecting a total of 750.7 connection hours
for such period for Full Internet Service Customers (peak time), 1,825.2
connection hours for Restricted Internet Services Customers (peak time), and
2,015.6 connection hours for all Off-Peak Access". A "connection" shall begin
when the CNC Network has validated a name and password, and terminate when the
modem "carrier dropped" message occurs whether triggered by a customer-initiated
disconnect or a shutdown of the connecting application. All Service Charges
under Standard Plans for all Customer/Service Categories for the Second Contract
Year commencing on the first anniversary of the Release Date shall be reduced
[*] for Full Internet Services Customers and from [*] for Restricted Internet
Services Customers. All Service Charges under Standard Plans for all
Customer/Service Categories for the Third Contract Year shall be reduced an
additional [*] from the rates charged in the Second Contract Year, e.g., from
                                                                   ----
[*] for Full Internet Customer Services Customers and from [*]/hour to [*]/hour
for Restricted Internet Services Customers.

          (2) Option to Convert Frequent User Standard Plan. After the date of
              ---------------------------------------------                   
this Amendment, Intuit by written notice to CNC may elect to convert its current
Frequent User Plan from a Standard Plan to a Package Plan on the following terms
and conditions for Customers that subscribe to such converted plan:

              (a) Usage and Customer Charges. The Customer will pay Intuit
                  --------------------------                              
[*] in advance for seven hours of usage, and [*] in arrears for each hour of
usage in excess of seven hours in the specified month.

              (b) Service Charges. As a part of the Monthly Reconciliation
                  ---------------  
Process, CNC will invoice Intuit for, and Intuit will pay CNC, (i) [*] for
each Intuit Frequent User Plan Customer that subscribed to such plan during the
applicable month, and (ii) [*] charged to such Customer for each hour of
"excess" usage by such Customer during the applicable month.

              (c) Additional Intuit Compensation. Additionally, as a part of the
                  ------------------------------                                
Monthly Reconciliation Process, CNC will pay Intuit a [*] "commission" for
each Customer who previously signed up for the Intuit Frequent User Plan and has
paid for at least two successive full months of service under the new Package
Plan arrangement.

                                       2

- ------------------
   [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.
<PAGE>
 
          b.   Package Plans. "Package Plans" are new arrangements implemented
               -------------
under this Amendment whereby Full Internet Services Customers are charged a
specified dollar amount for a certain number of hours of "free" usage per month
with monthly usage in excess of the free amount chargeable at a specified hourly
rate, and CNC is compensated as specified below. In the case that a given
package plan is "unlimited," the Customer may use an unlimited number of hours
for a specified monthly rate. Under Package Plans, CNC will not be paid its
normal hourly Service Charges (as noted above for Standard Plans) but, instead,
Intuit will pay Service Charges in another form to CNC as follows:

              (1) Usage and Customer Charges. The Customer will pay Intuit a
                  --------------------------                                
specified monthly rate in advance for a designated period of usage on a month-
to-month basis, and in arrears for any usage in excess of the "free" or included
monthly usage amount.

              (2) Service Charges. As a part of the Monthly Reconciliation
                  ---------------
Process, CNC will invoice Intuit for, and Intuit will pay CNC, a specified
monthly Service Charge for each Intuit Unlimited Plan Customer that subscribed
to such plan during the applicable month.

              (3) Additional Intuit Compensation. Additionally, as a part of the
                  ------------------------------                                
Monthly Reconciliation Process, CNC will pay Intuit a "commission" (sometimes
referred to as a "bounty") for each Customer who previously signed up for the
applicable Package Plan (including both former Standard Plan Customers and new
Customers) and has paid for at least a specified number of successive full
months of service. Commissions or bounties will be paid once during the
"lifetime" of a Customer when the Customer makes his/her first change from a
Standard Plan to a Package Plan. Additionally, CNC and Intuit will from time to
time review the amount and timing of the payment of the commission to determine
its fairness, and make such changes as the parties may mutually agree.

          c.  Prepaid Plans. "Prepaid Plans" are new arrangements implemented
              -------------
under this Amendment whereby Full Internet Services Customers can purchase a
specified level (which may be unlimited) of monthly usage effectively at a
discounted monthly fee if Customer pre-pays for a specified period. Under a
Prepaid Plan, CNC will not be paid its normal hourly Service Charges (as noted
above for Standard Plans) but, instead, Intuit will pay Service Charges in
another form to CNC as follows:

              (1) Usage and Customer Charges. The Customer will pay Intuit a
                  --------------------------                                
specified monthly rate in advance for the specified level of (or unlimited)
usage for a designated period of time, e.g.. pre-pay for six months at a monthly
                                       ----                                     
rate discounted from the normal "Package Plan" rate for unlimited monthly usage.

              (2) Service Charges. As a part of the Monthly Reconciliation
                  ---------------
Process, CNC will invoice Intuit for, and Intuit will pay CNC, a specified
amount per each Intuit Prepaid Plan Customer who subscribed to such plan during
the applicable month.

              (3) Additional Intuit Compensation. Additionally, as a part of the
                  ------------------------------                                
Monthly Reconciliation Process, CNC will pay Intuit a "commission" (sometimes
referred to as a "bounty") for each Customer (including both former Standard
Plan

                                       3
<PAGE>
 
Customers and new Customers) who previously subscribed for the Prepaid Plan if
such Customer has not canceled such subscription during a specified number of
full months of service under such plan. Commissions or bounties will be paid
once during the "lifetime" of a Customer when the Customer makes his/her first
change from a Standard Plan to a Prepaid Plan. Additionally, CNC and Intuit will
from time to time review the amount and timing of the payment of the commission
to determine its fairness, and make such changes as the parties may mutually
agree.

              (4) Cancellation. A Prepaid Plan may be cancelable by the
                  ------------
Customer. Any cancellation adjustments or penalties shall be set forth in the
applicable Plan Amendment (see subsection "d" below).

              (5) Continuation Services. In the event that a Customer does not
                  ---------------------                                       
notify CNC or Intuit that he/she intends to extend his/her Prepaid Plan, the
Customer will be notified (at the time of initially signing up for the Prepaid
Plan) that his/her service plan shall automatically revert to the comparable
Package Plan at the end of the applicable prepaid period.

          d.  Implementation of Plans. A list of the Package Plans and Prepaid
              -----------------------
Plans Intuit intends to implement as of the date of this Amendment is attached
hereto as Attachment "D-1". Subsequent changes to these new plans or the
creation of new Package and Prepaid Plans shall be implemented by the parties
through the execution and exchange of ""Plan Amendments" substantially in the
form of Attachment "D-2" hereto.

          e.  800# Telephone Services. CNC shall provide 800# telephone services
              -----------------------
to the Customers under Standard, Package and Prepaid Plans as a method for the
Customers to gain access to Intuit's Services. Intuit will charge the Customers
at an initial rate of [*] per hour for this service as a part of the periodic
billing of such Customers. Then, as a part of the Monthly Reconciliation
Process, CNC will invoice Intuit for, and Intuit will pay CNC, [*] at the
foregoing hourly charge for each hour of 800# service billed to the Customers
during the applicable month. Intuit and CNC will modify Customer charges, and
any amounts payable by Intuit related thereto, to account for changes in the
cost or pricing of 800# telephone services. Any 800# telephone charges shall be
in addition to any usage charges under the Customer's applicable Standard,
Package or Prepaid Plan.

     2.   Monthly Reconciliation Process.  Within 3 business days of the end of
          ------------------------------                                      
each calendar month, CNC shall conduct a "Monthly Reconciliation" as follows:

          a.  Prepare and deliver to Intuit a report containing (A) the usage,
customer service and performance information described in Exhibit "A", and (B)
the "Cumulative Service Charges" chargeable to Intuit for the applicable
calendar month, net of all applicable penalties, credits and reimbursements
calculated as follows: (i) the chargeable time and related cumulative Service
Charges for each Plan/Customer/Service Category (Full, Restricted, Non-Internet
Traffic, and Off Peak Access) plus (ii) the amount of any Forecast Shortfall
                              ----                                          
Penalty (calculated pursuant to Item (1) below), if any, minus (iii) financial
                                                         -----                
penalties for CNC's failure to meet Performance Standards (see Item (2) below),
if any, plus (iv) any amounts owed to Intuit for Customer Service Charges
        ----                                                             
reimbursable by CNC pursuant to Exhibit "C" of the Agreement, minus (v) any
                                                             -----        
amounts owed by Intuit to CNC for Customer Service charges

                                       4

- ------------------
   [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.
<PAGE>
 
reimbursable by Intuit pursuant to Exhibit "C" of the Agreement, plus or minus
                                                                 -------------
(vi) any other adjustments agreed to between the parties. CNC shall also include
an invoice for the Cumulative Service Charges, as adjusted pursuant to this
Agreement, and Intuit shall pay such invoice within thirty days of its receipt.

          (1) Forecast Shortfall Penalty. Within ten days of its receipt of
              --------------------------                                   
CNC's Monthly Reconciliation, Intuit will develop and provide to CNC a non-
binding rolling forecast of anticipated CNC Network usage by the Customers
subscribing to Standard Plans for the next three calendar months. To the extent
that the actual volume of forecasted hours under Standard Plans for a given
month is less than [*] of Intuit's most recent estimate of forecasted hours for
such month, Intuit will pay CNC the difference between the actual volume of
usage under Standard Plans and [*] of the most recent estimate for Standard Plan
usage for such month using the then effective Restricted Internet Services
hourly charge; provided, however, that Intuit shall not be subject to the
foregoing Forecast Shortfall Penalty if the actual number of Customers who
subscribe for Package and Prepaid Plans for the applicable month is at least [*]
of the number forecasted by Intuit in its most recent monthly forecast for such
month. By way of illustration, if (i) Intuit's most recent forecast in December,
1995, estimated an aggregate total Customer usage under Standard Plans for
January, 1996 of [*] hours and the actual usage for January was [*] hours
and (ii) Intuit achieved only [*] of its aggregate estimate for forecasted users
under both its Package Plans and Prepaid Plans, then Intuit would be required to
compensate CNC at the foregoing rate for the difference between [*] hours and
[*] hours (i.e., [*] of the most recent estimate of [*] hours).

          (2) CNC Performance Financial Penalty. This credit will be an amount
              ---------------------------------                               
equal to the financial penalties payable by CNC to Intuit established pursuant
to Exhibit "A" of the Agreement.

          b.  Prepare and deliver (or make available for Intuit's ready on-line
access) to Intuit a Customer Charge report reflecting the number of connect
hours for each Customer, the amount of Customer Charges billed to Customers, the
amount of payments billed to and received from Customers, the amount of any
credits given to Customers, and other related billing or financial information
reasonably requested by Intuit. Additionally, CNC will deliver or make available
on-line to Intuit a report showing all charges to and collections from Customers
on a cumulative basis ("Monthly Customer Collections") including names, billing
numbers, Internet name, anniversary date, time used per billing period and
connection, payment plan, e-mail preference, pay type, and other information
reasonably requested by Intuit.

     3.   CNC Termination Right. DELETED (no longer applicable)
          ---------------------                                

B.   CUSTOMER CHARGES AND INFORMATION STATEMENTS

     Intuit will establish the Customer Charges from time to time in its sole
discretion. As a part of the CNC Services, CNC shall deliver or make available
by December 31, 1995 usage, account and billing information on a continuous
basis to Intuit and all Customers (whether for Restricted or Full Internet
Services) through on-line access such as hours/month usage, charges/credits, and
other information reasonably requested by Intuit (the "lnformation Statement").
Additionally, upon Customer request,

                                       5

- ------------------
   [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.
<PAGE>
 
CNC shall mail a hard copy of the Information Statement to such Customer. Prior
to December 31, 1995, Customers may call CNC to obtain their billing and account
status.

C.   CNC REPORTING

     1.   Initial Reporting. During the period prior to January 1, 1996, CNC and
          -----------------                                                    
Intuit will define, develop and implement reporting requirements. During this
initial period, CNC will use its reasonable best efforts to provide Intuit
with requested information, but Intuit acknowledges that CNC's initial reporting
will be minimal.

     2.   Ongoing Reporting. Not later than January 1, 1996, CNC will implement
          -----------------                                                   
the report set agreed to between the parties on a monthly basis including
information such as:
<TABLE>

    <S>                                                          <C> 
     New Subscribers/month (Actual)              -                Standard Plans (Restricted           
                                                                  Access, Full Access accounts by      
                                                                  type of usage plan), Package         
                                                                  Plans, and Prepaid Plans.            
                                                                                                       
     Total # Base Subscribers/month              -                (same breakdown as above)            
                                                                                                       
       (including New)                                                                                 
                                                                                                       
     Average Personal Usage/month                -                 (same breakdown as above)           
                                                                                                       
     Peak hours/day                              -                 Number of subscribers (same         
                                                                   breakdown), number of hours         
                                                                                                       
     Peak day/week                               -                 (same breakdown as "per day"        
                                                                    report)                            
                                                                                                       
     Number of inactive accounts                 -                 not used in a month per             
                                                                   Customer/Service category           
                                                                                                       
     Customer Service Calls                      -                 (breakdown to be developed)          
</TABLE> 

D.   INTUIT FORECASTING
 
     1.   Initial Forecasting. On an ongoing basis during the term of this
          -------------------
Agreement, CNC and Intuit will define, develop and implement forecasting
requirements.

 
     2.   Ongoing Forecasting. Not later than January 1, 1996, Intuit will
          -------------------
implement the forecasting set agreed to between the parties including
information such as:
<TABLE> 
    <S>                                                          <C>  
     Estimated New Subscribers/month             -                 Standard Plans (Restricted
                                                                   Access, Full Access
                                                                   accounts by type of plan),
                                                                   Package Plans and Prepaid
</TABLE> 

                                       6
<PAGE>
 
<TABLE> 
    <S>                                                           <C>  
                                                                   Plans

     Estimated Total # Base                       -                (same breakdown as above)
      Subscribers/month

     Estimated Average Personal                   -                Standard Plans Only
      Usage/month
</TABLE> 

Intuit's forecast shall be a rolling 90 day forecast updated on a monthly basis.
For example, in December 1995, Intuit would make its forecast for the
immediately following January, February and March 1996. Then, in January 1996,
Intuit would issue an updated forecast for the immediately following February
and March, and makes its initial forecast for April. As noted in Section
D.2.(b)(5) of Exhibit "A", CNC shall not be held responsible for failing to
achieve those Performance Standards adversely affected by a situation where
Intuit's initial forecast for a month underestimates actual network usage or
customer service calls by more than 20%; provided, however, that CNC will use
its reasonable best efforts to adjust to changes in Intuit's forecasts and the
actual volumes experienced at any given time so as to attempt to achieve such
Performance Standards."

     3.   The parties acknowledge and agree that the reconciliation, reporting
and forecasting of procedures described in Exhibit D shall be deemed amended to
include applicable information for the Package and Prepaid Plans.

     4.   Intuit's address for notifications given pursuant to Section 8.1 of
the Agreement is hereby modified to the address specified below.

     5.   Except as otherwise provided in this Amendment, the terms and
conditions of the Agreement remain in full force and effect.

     IN WITNESS WHEREOF, the parties have executed and delivered this Amendment
as of the Effective Date and it shall be deemed accepted and made in San Diego,
California.

INTUIT INC.                            CONCENTRIC NETWORK
                                       CORPORATION


By: /s/ WILLIAM HARRIS                 By: /s/ MICHAEL ANTHOFER
   --------------------------             ------------------------
   William Harris                         Michael Anthofer
   Executive Vice President               Chief Financial Officer

   6220 Greenwich Drive                   10590 North Tantau Avenue
   San Diego, CA 92122                    Cupertino, CA 95014

                                       7
<PAGE>
 
                                ATTACHMENT "D-1"
                       PACKAGE AND PREPAID PRICING PLANS

A.   PACKAGE PLAN

     1.   "lntuit Unlimited Plan"
           --------------------- 

          (a) Usage and Customer Charges. The Customer will pay Intuit
              --------------------------
[*]/month in advance for unlimited usage on a month-to-month basis.

          (b) Service Charges. As a part of the Monthly Reconciliation Process,
              ---------------
CNC will invoice Intuit for, and Intuit will pay CNC, [*] for each Intuit
Unlimited Plan Customer that subscribed to such plan during the applicable
month.

          (c) Additional Intuit Compensation. Additionally, as a part of the
              ------------------------------
Monthly Reconciliation Process, CNC will pay Intuit a [*] "commission" for
each Customer who previously signed up for the Intuit Unlimited Plan and has
paid for at least two successive full months of service.

                                       8
- ------------------
   [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

<PAGE>
 
                                ATTACHMENT "D-2"

                          FORM OF PLAN AMENDMENT UNDER
            INTERNET ACCESS SERVICES AGREEMENT DATED AUGUST 1, 1995

Name of Plan:
- -------------

Category of Plan (circle one): Standard   Package    Prepaid
- -----------------------------                               

Usage and Customer Charges: [TBD]
- --------------------------       

Service Charges: As a part of the Monthly Reconciliation Process, CNC will
- ---------------                                                           
invoice Intuit for, and Intuit will pay CNC, $___  per each Intuit Plan Customer
who subscribed to such plan during the applicable month.

Additional Intuit Compensation. Additionally, as a part of the Monthly
- ------------------------------                                        
Reconciliation Process, CNC will pay Intuit a $__ commission for each Customer
who previously subscribed for the Plan if such Customer has not canceled such
subscription during the first _____ full months of service under such plan. The
amount and timing of the payment of this commission will be reviewed, and if
mutually agreed upon, reset by CNC and Intuit every ___ months.

Cancellation Provisions: [TBD]
- -----------------------       

Former Plan replaced by this Plan (if applicable): [TBD]

Other terms and conditions: [TBD]
- --------------------------       


This Plan Amendment is effective as of ______________, 199_, and subject to all
of the terms and conditions of the Agreement.

INTUIT INC.                            CONCENTRIC NETWORK
                                       CORPORATION


By:                                    By:
   ---------------------------            ---------------------------
   Officer:                               Officer:
           -------------------                    --------------------
   Title:                                 Title:
         ---------------------                  ----------------------

6256 Greenwich Drive, Suite 100          10590 North Tantau Avenue
San Diego, CA 92122                      Cupertino, CA 95014

                                       9
<PAGE>
 
                              AMENDMENT NO. 2 TO
                      INTERNET ACCESS SERVICES AGREEMENT


THIS AMENDMENT NO. 2 TO INTERNET ACCESS SERVICES AGREEMENT ("Amendment") is made
and effective as of October 31, 1996 (the "Effective Date"), by and between
                            --                                             
Intuit Inc., a Delaware corporation ("Intuit"), and Concentric Network
Corporation, a Florida corporation ("Concentric" or "CNC"), with reference to
the following facts:

                                    RECITALS
                                    --------

A.   Intuit and CNC are parties to that certain Internet Access Services
     Agreement effective as of August 1, 1995, as amended by that certain
     Amendment No. 1 to Internet Access Services Agreement dated August 15,
     1996, and as the meaning of certain of its provisions were confirmed
     pursuant to that certain Acknowledgment and Limited Waiver dated August
     20, 1996 (collectively, the "Agreement").

B.   Intuit and CNC desire to amend the Agreement to incorporate an additional
     network performance standard regarding network accessibility.

     NOW, THEREFORE, for valuable consideration, the parties hereto agree as
follows:

1. Except as otherwise defined herein, capitalized terms shall have the meaning
   given them in the Agreement.

2. Exhibit "A", Section C, sub-sections 2b and 2c entitled "Network Processing
   Capacity Performance Standards (Latency)" and "Customer Service/Support
   Performance Standards," respectively, are hereby re-labeled as sub-sections
   2c and 2d, respectively.

3. Exhibit "A", Section C, sub-section 2 entitled "Performance Standards" is
   hereby amended to include the following sub-section 2b:

     "b.  Network Connection Success Performance Standard. The CNC Network shall
          -----------------------------------------------                       
achieve average successful connection rates at or above the following
Performance Standards for Intuit Customers attempting to access the CNC Network:

     Target Performance Standard:
     --------------------------- 

          [*] "successful connection" rate for VLA-type POP sites

          [*] "successful connection" rate for physical-type POP sites

                                       1

- ------------------
   [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

<PAGE>
 
     Minimum Performance Standard:
     ---------------------------- 

          [*] "successful connection" rate for VLA-type POP sites

          [*] "successful connection" rate for physical-type POP sites

Comments:
- -------- 

     (1) CNC shall employ a PC-based dial/connection-tool software acceptable to
Intuit to measure the successful connection rates of the CNC Network.

     (2) CNC shall conduct testing of the successful connection rates for the
CNC Network on a regularly scheduled basis, but no less often than once per
calendar month. During the monthly test period, each POP site in the CNC Network
shall be tested at least once as specified in Comment (3) below.

     (3) The duration of the test period shall be at least a continuous 24 hour
period to satisfy the parties' intention of testing the CNC Network during both
daily peak and off-peak hours. CNC shall use a PC based dial/connection tool
similar to the Gage Access ISP poll software using a Windows 95 PC
configuration, with a standard TCP/IP stack/dialer and a mutually acceptable
consumer modem. The network will be tested by accessing at least [*] of the CNC
local access phone numbers in the continental United States and Canada during
the testing period.

     (4) A "successful connection" is defined as a test call in which the
dial/connection-tool software calls into a designated CNC Network POP site,
negotiates a connection session, logs into the CNC Network, accesses a www html
test page or pings a designated web site, and disconnects from the CNC Network.
Further, CNC shall use commercially reasonable efforts to ensure that the test
sessions are structured so that the dial/connection-tool software accurately
recreates the Intuit customer experience, e.g., by incorporating variables in
connection rates for different modem types, dialers, times of day, POP types
(VLA and physical), modem speed and Intuit-specific login procedures. Although
Modem incompatibility problems will be excluded from the final test results, CNC
will implement a mutually acceptable action plan to correct modem
incompatibility problems that occur with the modem types that account for the
top [*] of all units sold in the United States and Canada, as applicable.

     (5) The test call shall be excluded from the calculation of overall test
results if the dial/connection-tool software establishes a connection but
experiences an error condition. By way of example, a call in which a Windows95
remote access Service error condition is logged would not be counted as an
attempted call in the tabulation of test results.

     (6) The successful connection rates shall be calculated as follows:

                                       2
- ------------------
   [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

<PAGE>
 
         (a) First, the overall "successful connection" rate for each physical
and VLA-type POP sites shall be determined on a POP-by-POP basis by (A)
tabulating the total number of test calls initiated by the dial/connection-tool
software and the corresponding number of successful connections reported by the
dial/connection-tool software, (B) adjusting the total number of test calls
downward for any dial/connection tool software error conditions, and (C)
dividing the number of test calls that achieved successful connections by the
total number of test calls. By way of example, assume the CNC Network had only
2 physical-type POPs and the dial/connection-tool software tests yielded the
following results:

<TABLE>
<CAPTION>
 
         POP       Total     Adjusted      Successful      Successful  
                   Test       Total       Connections      Connection   
                   Calls      Test                           Rate      
                              Calls                                    
      <S>         <C>        <C>         <C>              <C>        
         #1         30          29             27             93.1     
         #2         38          38             36             94.7     
       Totals       68          67             63             94.0      
</TABLE>

          (b) Second, the weighted average of the "successful connection" rate
shall be calculated for all POPs of one type in the CNC Network. This weighted
average shall be calculated based on the number of ports at each POP. By way of
example, assuming the CNC Network only had 2 physical-type POPs with the
following number of ports and achieved the successful connection rates as
calculated in Comment (6)(a) above, the weighted average for this 120 port
physical POP network as a whole would be 0.9406 (or 94.06%) as indicated in the
following table:
<TABLE>
<CAPTION>
                                     
         POP           POP               Port             Weighting         Weighted 
                    Successful         Count at             Factor           Average 
                    Connection        applicable          (based on         Successful 
                      Rate               POP                number          Connection  
                                                           of ports)           Rate
        <S>        <C>               <C>                 <C>               <C>
          #1           93.1               48                   .4              37.24
          #2           94.7               72                   .6              56.82
        Totals         94.0              120                  1.0              94.06%
</TABLE>

A separate weighted average calculation would be performed for VLA-type POPs in
the CNC Network.

          (c) Finally, the overall weighted average successful connection rate
for the CNC Network as calculated above would be compared to the applicable

                                       3
<PAGE>
 
Performance Standard to determine whether or not CNC had achieved its Network
Connection Success performance goal for the applicable calendar month. By way of
example, a comparison of the weighted average successful connection rate of
[*] for the above physical POPs to the physical-type POP Target Performance
Standard of [*] and the Minimum Performance Standard of [*] reflects that CNC
has satisfied both performance standards in this performance metric.

     (7)  The monthly CNC Network successful connection test results will be
reported to Intuit as required pursuant to the Agreement. Each POP-type category
(i.e., VLA and physical) must satisfy its respective performance standard for
the CNC Network to satisfy this performance standard.

     (8)  CNC will develop within one week and execute a corrective action plan
acceptable to Intuit to bring into conformance with the applicable Performance
Standard any Point of Presence that falls below a [*] successful connection
rate. If CNC's corrective action plan requires that it obtain network services
from third parties, then the timetable for the execution of such plan will take
into consideration the delivery dates for such third party services. CNC's
failure or inability to execute the corrective action plan to remedy the problem
shall be deemed to be a failure to satisfy the applicable Performance Standard
for this measure.

     (9)  From time to time, the parties shall evaluate the level of this
performance standard compared to the network successful connection rates
achieved by other high quality Internet service providers as provided in Exhibit
"A", Section C.1."

4. Except as otherwise provided in this Amendment, the terms and conditions of
the Agreement remain in full force and effect.

     IN WITNESS WHEREOF, the parties have executed and delivered this Amendment
as of the Effective Date and it shall be deemed accepted and made in San Diego,
California.


INTUIT INC.                            CONCENTRIC NETWORK
                                       CORPORATION


By: /s/ WILLIAM HARRIS                 By: /s/ MICHAEL ANTHOFER
   --------------------------             ---------------------------
   William Harris                         Michael Anthofer
   Executive Vice President               Vice President and CFO

   6220 Greenwich Drive                   10590 North Tantau Avenue
   San Diego, CA 92122                    Cupertino, CA 95014

                                       4
- ------------------
   [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

<PAGE>
 
                     PRICING PLAN ADDENDUM NO. 1 PURSUANT
                     TO INTERNET ACCESS SERVICES AGREEMENT

                  Name of Plan: "Intuit 6 Month Prepaid Plan"
                                 --------------------------- 

          (a) Usage and Customer Charges. Intuit will charge a new Customer
              --------------------------
(i.e., one who is not currently registered with Intuit for full Internet access)
[*] in advance for [*] months of unlimited network usage, apportionable to one
free month of full Internet access followed by 6 months of full Internet access
at the rate of [*]/month. Existing full Internet access Customers switching
from another Intuit plan to this Prepaid Plan will be charged [*] in advance
for 6 months of full Internet access, apportionable at the rate of [*]/month.

          (b) Service Charges. As a part of the Monthly Reconciliation Process, 
              ---------------  
CNC will invoice Intuit for, and Intuit will pay CNC, [*] for each Intuit
Customer that subscribes to this Prepaid Plan during the applicable month.

          (c) Additional Intuit Compensation. Additionally, as a part of the
              ------------------------------                                
Monthly Reconciliation Process, CNC will pay Intuit an [*] "commission" for
each Customer who previously signed up for this Prepaid Plan and has been active
on the service for at least three successive full months of service. Customers
who have converted from a Package Plan to this Prepaid Plan after 60 days of
active paid service will not be included in the calculation of the foregoing
commission payable by CNC for this Prepaid Plan.

          (d) Cancellation. If a Customer under this Prepaid Plan cancels before
              ------------                                                      
the completion of the full six month "paid" term, then they will be treated as
an Intuit Unlimited Package Plan customer (i.e., [*]/month for unlimited use)
and refunded accordingly. By way of example, an existing Customer who canceled
on or before the third anniversary date would be refunded [*]. A new Customer
will receive credit for the first free month, so if they canceled on or before
the third anniversary date they would be refunded [*] for the four remaining
months that were not used.

          (e) Continuation of Services. When customers sign up for this Prepaid
              ------------------------                                         
plan they will be notified that they will revert to Intuit's Unlimited Package
Plan at the end of the subscription period (i.e., currently [*]/month for
unlimited use).


Effective Date: October 15, 1996

INTUIT INC.                            CONCENTRIC NETWORK
                                       CORPORATION


By: /s/ WILLIAM HARRIS                 By: /s/ MICHAEL F. ANTHOFER
   ----------------------------           ----------------------------- 
Name: Bill Harris                      Name: Michael F. Anthofer
     --------------------------             ---------------------------
Title: Executive Vice President        Title: VP & CFO
      -------------------------              --------------------------

6220 Greenwich Drive                   10590 North Tantau Avenue
San Diego, CA 92122                    Cupertino, CA 95014

- ------------------
   [*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

<PAGE>
 
                                                                   EXHIBIT 10.32

               Revised Virtual Private Network Services Agreement
               --------------------------------------------------


       This agreement is made and entered into effective as of the 1st day
       of February, 1997 ("Effective Date") by and between Concentric
       Network Corporation ("CNC"), a Florida corporation with offices at
       10590 N. Tantau Avenue, Cupertino CA 95014, and WebTV Networks Inc.
       ("WNI"), a California corporation located at 275 Alma Street, Palo
       Alto, CA 94301.
       
       WHEREAS CNC currently provides local access by telephone to a
       significant portion of the personal computer user population in the
       top geographical markets in the United States and Canada;
       
       WHEREAS CNC plans to expand, improve and enhance the capabilities of
       its network;
       
       WHEREAS WNI has developed a "WebTV" television set top appliance
       which allows its customers to use their televisions to access
       Internet services such as E-mail, World Wide Web, chat, and UseNet,
       and WebTV proprietary on-line services;
       
       WHEREAS WNI plans to operate computers that will act as servers to
       facilitate such Internet access, as well as registration, account
       verification, technical support, billing, collection, and inquiry
       functions;
       
       WHEREAS WNI wishes to obtain from CNC, and CNC wishes to provide to
       WNI, dial-up access and network services to implement WebTV Services,
       as defined herein; and
       
       WHEREAS the parties entered into a Virtual Private Network Services
       Agreement dated August 16, 1996, as supplemented by the Addendum
       dated December 1, 1996 and as amended by the Amendment dated January
       7, 1997, and wish this Agreement to supersede such documents.
       
       NOW, THEREFORE, in consideration of the mutual promises set forth
       herein, the parties agree as follows:
       
1.     DEFINITIONS
       
       The following capitalized terms shall have the following meaning when
       used in this Agreement:
       

                                       1
<PAGE>
 
1.1.   "800 Service" shall have the meaning set forth in Section 2.9.
       
1.2.   "Agreement" shall mean this Revised Virtual Private Network Services
Agreement, including its exhibits and attachments, all by this reference
incorporated into and made a part hereof.
       
1.3.   "CNC Equipment" shall be the computer and telecommunications equipment
set forth in Exhibit A under the corresponding caption.

1.4.   "Customer Information" shall mean all the information and records
collected, processed or compiled by CNC, including without limitation, lists of
customer names, addresses, and telephone numbers; registration, credit and
financial information, and information respecting customer needs, usage and
demands.

1.5.   "Dedicated Access Facilities" shall have the meaning set forth in
Section 2.7.

1.6.   "Engineering Unit" shall have the meaning set forth in Section 2.3.

1.7.   "Point of Presence" shall mean the hardware (such as modems, terminal
servers and routers), software, networks and telecommunications connections at a
local facility or site through which an end user may gain access to the Internet
through a telephone TCP/IP link with the Virtual Private Network Services.

1.8.   "Project Manager" shall have the meaning set forth in Section 2.4.

1.9.   "Third Party Software" shall have the meaning set forth in Section 2.5.

1.10.  "Subscribers" shall mean customers who utilize WebTV Services.

1.11.  "Subscriber Minute" shall be a minute or a portion thereof when a WNI
Subscriber is using the 800 Service.

1.12.  "Term" shall have the meaning set forth in Section 6.1.

1.13.  "Transition Date" shall have the meaning set forth in Section 2.7.

1.14.  "Virtual Port" shall mean the simultaneous modem connection of a 
Subscriber to the Virtual Private Network Services.

1.15.  "Virtual Port Commitment" shall mean the minimum number of Virtual Ports
for which WNI will pay Virtual Port Fees each month pursuant to Section 4 and 5.

1.16.  "Virtual Port Fees" shall mean fees payable to CNC by WNI for the use of
Virtual Ports as set forth in Section 5.

                                       2
<PAGE>
 
1.17.  "Virtual Private Network Services" shall mean the computing, information
services, hardware, software, telecommunications, access and provisioning
provided by CNC as further described in this Agreement, as such network may be
enhanced, improved and/or expanded during the Term, including without limitation
the software and technology enabling a Point of Presence, and other software,
including object code and source code, and including any related documentation.

1.18.  "WebTV Equipment" shall be the computer and telecommunications equipment
set forth on Exhibit A under the corresponding caption.

1.19.  "WebTV Services" shall mean the Internet access and other computing and
information services, provided by WNI in connection with its WebTV service, as
such service may be modified, improved and expanded during the Term.

2.     CNC SERVICES/RESPONSIBILITIES
       -----------------------------

2.1.   CNC Access. CNC shall provide the Virtual Private Network Services 
       ----------
through its Points of Presence, which shall at all times include Points of
Presence in no less than [*] of the top [*] metropolitan areas in the United
States.

2.2.   UseNet. CNC will provide WNI with a UseNet newsfeed. The price of the
       ------
newsfeed will be included in the monthly service fees of the Dedicated Access
Facilities. However, upon WNI's request, CNC shall provide the alt.* hierarchy
at an additional fee of [*] per month.

2.3.   Information and Operational Support System Interfaces. The parties
       -----------------------------------------------------
acknowledge that CNC has delivered software tools by which WNI can monitor the
usage and performance of CNC's network as used in the Virtual Private Network
Services. Subject to mutual agreement as to the specifications therefore, CNC
shall, at WNI's request, perform additional development and maintenance of
related software at the rate of [*].

2.4.   Project Manager. CNC shall assign WNI a dedicated project manager 
       ---------------
for the Term to serve as CNC's primary contact to WNI ("Project Manager"). The
Project Manager shall be available during business hours as needed by WNI to
assist WNI in problem resolution, monthly reviews, and process improvement
efforts. [*].

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       3
<PAGE>
 
2.5.   Third Party Software. The parties acknowledge that each party is and
       --------------------
will be using its own software to verify the identity and account of Subscribers
("Third Party Software"). The parties further acknowledge that any rights or
licenses in the Third Party Software shall be directly between any applicable
third party and the applicable party.

2.6.   General Network Operation. CNC shall use commercially reasonable efforts
       -------------------------
to operate the Virtual Private Network Services seven (7) days per week, twenty
four (24) hours per day, three hundred sixty-five (365) days per year. CNC shall
provide services under this Agreement which meet the best commercially
reasonable. CNC will respond to any network outages pursuant to the escalation
procedures set forth in Exhibit C and, as part of such responses, CNC will use
all commercially reasonable efforts to implement such actions as are appropriate
so as to maintain the services under the terms of this Agreement.

2.7.   Dedicated Access Facility. The parties acknowledge that prior to the
       -------------------------
Effective Date, CNC has delivered, and will continue to provide, the Dedicated
Access Facility and the CNC Equipment, which shall mean the D53 and other
mutually agreed upon access solutions set forth in Exhibits A and B, pursuant to
the terms and conditions set forth in Exhibit B., pursuant to the terms set 
forth in Exhibit B. CNC acknowledges that such listed WNI Equipment will be
sufficient to allow CNC to provide the services which it is obligated to provide
under this Agreement. CNC's response to any problems in the Dedicated Access
Facilities will be pursuant to the procedures set forth in Exhibit D. And, as
part of such response, CNC shall use all commercially reasonable responses to
implement such actions as are appropriate so as to maintain the services under
the terms of the Agreement.
 
2.8.   Connectivity to the Internet. The parties acknowledge that CNC has 
       ----------------------------
provided and will continue to provide direct access between WNI's data centers
and the Internet, pursuant to the terms and conditions set forth in Exhibit B
including the terms and conditions specified under the caption "Additional
Explanations".

                                       4
<PAGE>
 
2.9.   800 Service. In addition to the Point of Presence access described in
       -----------
Section 2.1, CNC shall make available to WNI Virtual Private Network Services
that access a Point of Presence through a toll-free 800 line to be provided by
CNC, which shall be available in the 48 contiguous states of the United States
in areas where there is no local CNC Point of Presence ("800 Service"), subject
to the fees set forth in Section 5.3.

3.     MUTUAL RESPONSIBILITIES
       -----------------------

3.1.   Improving Performance.  CNC and WNI shall work together to define 
       ---------------------
programs to continually improve the performance of the Virtual Private Network
Services for Subscribers, and CNC shall, upon mutual, prior written agreement,
implement such programs. The parties shall share the expense for such programs
in a manner to be mutually determined.

3.2.   Technical Support. WNI shall provide first tier support directly to
       -----------------
Subscribers. CNC shall provide second tier technical support to WNI pursuant to
the provisions of this Section 3.2 and the escalation policies described in
Exhibit C and Exhibit D. CNC shall provide to WNI a telephone support line
connected to CNC's network operations desk, staffed by CNC employees
knowledgeable regarding the network services offered by CNC. CNC shall operate
such telephone support line twenty four (24) hours per day, seven (7) days per
week, three hundred sixty five (365) days per year.

3.3.   Publicity. WNI and CNC will jointly develop and agree on an appropriate
       ---------
set of responses and/or statements to be used when responding to press or other
third-party inquiries regarding the WNI/CNC relationship described in this
Agreement, with the objective of providing positive referral and support for
each company in these communications. Each party shall restrict its public
comments to such agreed upon responses, except as otherwise mutually agreed or
as required by law. [*].

3.4.   Statistical Information.  WNI and CNC will disclose to each other to
       -----------------------
the extent that it is reasonably available statistical information [*]. Such
information shall be subject to the terms of Sections 8.2 and 8.3.

4.     VIRTUAL PORT FORECASTS AND COMMITMENTS
       --------------------------------------

4.1.   Rolling Forecasts. Each calendar quarter after the Effective Date,
       -----------------
WNI shall provide CNC a non-binding rolling forecast of the Virtual Ports it
anticipates it will use during the ensuing twelve (12) month period. CNC and WNI
shall meet and discuss these Virtual Port Forecasts on a quarterly basis.


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       5
<PAGE>
 
4.2.   Virtual Port Commitment. For the period February through [*]
       -----------------------
WNI's minimum Virtual Port Commitment shall be [*] Virtual Ports per month.
For the period [*] the minimum Virtual Port Commitment shall be [*] Virtual
Ports per month. The parties will negotiate in good faith to determine the
Virtual Port Commitment for the period after [*].

5.     VIRTUAL PORT FEES.
       -----------------

5.1.   Virtual Port Fees.  WNI shall pay CNC Virtual Port Fees based on 
       -----------------
Virtual Port Commitment and actual usage as follows:

<TABLE>
<CAPTION>
        Time Period            Virtual Port Commitment            Additional Virtual Ports
        -----------            -----------------------            ------------------------
   <S>                          <C>                               <C>
   February - [*]               [*]                                [*]
   [*]                          [*]                                [*]
</TABLE>

For February and March 1997, WNI will pay CNC for the Virtual Port Commitment
listed above, or actual peak simultaneous users, whichever is higher. For the
months of [*], WNI will pay CNC for either the Virtual Port
Commitment listed above or [*].
 
5.2.   Renegotiation. WNI and CNC agree to negotiate in good faith new 
       -------------
pricing, terms, and conditions by [*]. If the parties cannot agree on new
pricing, terms and conditions by [*] WNI increases its [*] over levels in
effect on the Effective Date or adds an hourly component to its pricing, then
CNC reserves the right to request an immediate re-negotiation of the fees it
charges WNI, and if such re-negotiation is not satisfactorily completed within
[*] of such request, CNC reserves the right to cancel this Agreement upon [*]
prior notice to WNI.
 
5.3.   800 Service. For 800 Service rendered from the Effective Date until
       -----------
[*] WNI shall pay CNC at [*] per Subscriber Minute. For 800 Service rendered
from May 1, 1997 until September 30, 1997, WNI shall pay CNC at the rate of
[*] per Subscriber Minute. In each case, such fees shall be in addition to the
Virtual Port Fees due under Section 5.1. The parties will negotiate in good
faith to determine the 800 Service fees to be effective after [*].

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       6
<PAGE>
 
       5.3.1.  Daytime Surcharges.  In the event that more than [*]
               ------------------ 
       of Subscriber Minutes occur [*], Pacific Time, WNI shall pay CNC an
       additional [*] for each such Subscriber Minute.

       5.3.2.  Intrastate Surcharges.  WNI shall pay CNC an additional 
               ---------------------
       [*] for each Subscriber Minute that consists of an intrastate call
       (from a Subscriber to a Point of Presence in the same state). CNC will
       reroute traffic to avoid Intrastate Surcharges wherever possible. If
       CNC is not able to reroute traffic then WNI will be responsible for any
       Intrastate Surcharges that are accrued.

5.4.   Taxes. WNI shall reimburse CNC for all Taxes related to the 800 service,
       -----
and Dedicated Access Facilities; except any taxes based on the net income of
CNC. All other taxes shall be borne by CNC.

5.5.   Payment. CNC shall invoice WNI for Virtual Port Fees and 800 Service
       -------
fees as follows. In advance for each month, on the first day of each month, CNC
shall invoice WNI based on the Virtual Port Commitment applicable for that month
(for Virtual Port Fees) and the last month's actual usage (for 800 Service
fees). On the first of the following month, CNC will bill WNI for any adjustment
necessary (plus or minus) to reconcile the prior month's billing with the prior
month's actual usage. All payment terms will be net thirty (30) days. If bill
has not been paid by the due date, CNC will give WNI written notice with ten
(10) days to cure. [*]. If WNI fails to pay an invoice for 800 Service when
due, CNC reserves the right to discontinue 800 Service until payments are
made, after WNI has been given written notice of failure to pay and has failed
to cure within 10 days.

5.6.   Dedicated Access Facilities.  [*].
       ---------------------------

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       7
<PAGE>
 
6.     TERM AND TERMINATION.
       --------------------

6.1.   Term. The term of this Agreement shall commence on the Effective Date and
       ----
continue until December 1, 1997, unless earlier terminated in accordance with
this Section 6. At the expiration of this initial term, this Agreement shall
continue in effect indefinitely, unless and until terminated in accordance with
Section 6.2. The initial term and any continuing term shall collectively be the
"Term."

6.2.   Termination By Either Party.  This Agreement may be terminated by
       ---------------------------
either WNI or CNC as follows:

       6.2.1.  Termination At Will.  At any time on or after September 30, 1997
               -------------------
       either party may terminate this Agreement, for any reason or no reason,
       upon one hundred and twenty (120) days' notice.
 
       6.2.2.  Uncured Material Breach. Either party may terminate this
               -----------------------
       Agreement upon written notice for any material breach of this Agreement
       which the other party fails to cure within thirty (30) days following
       written notice of such breach by the non-breaching party.

       6.2.3.  Insolvency. Either party may, upon ten (10) days' written notice,
               ----------
       terminate this Agreement in the event that the other party becomes
       insolvent, liquidates, makes an assignment for the benefit of creditors,
       or ceases to do business in the ordinary course for a continuous period
       of more than one (1) week.

6.3.   Effect of Termination and Survival of Terms. Termination of this 
       -------------------------------------------
Agreement shall be without prejudice to any rights or remedies available to
either party arising prior to such termination by reason of breach of this
Agreement. The provisions of Sections 1, 7, and 8 shall survive expiration or
termination of this Agreement for any reason.

7.     INDEMNIFICATION
       ---------------

7.1.   Indemnification by WNI: WNI agrees to, and shall, defend and hold
       ----------------------
harmless CNC, and its and their directors, shareholders, officers, agents and
employees, from and against any and all suits, actions, damages, costs, losses,
expenses (including attorneys' fees) and other liabilities arising in whole or
in part from or in connection with (a) WNI's breach of this Agreement or (b) any
claim or allegation that WebTV Services or the use of WebTV Services violates
any U.S. patent or other U.S. intellectual property rights of a third party.

                                       8
<PAGE>
 
7.2. Indemnification by CNC: CNC agrees to, and shall, defend and hold harmless
     ----------------------
WNI, and its and their directors, shareholders, officers, agents and employees
from and against any and all suits, actions, damages, costs, losses, expenses
(including attorneys' fees) and other liabilities arising in whole or in part
from or in connection with (a) CNC's breach of this Agreement or (b) any claim
or allegation that the Virtual Private Network Services or the use of the
Virtual Private Network Services violates any U.S. patent or other U.S.
intellectual property rights of a third party.

7.3. Conditions: The indemnities set forth in Sections 7.1 and 7.2 shall be
     ----------
conditioned upon the indemnified party promptly notifying the indemnifying party
in writing of any such claim, suit, expense or the like. The indemnifying party
shall bear full responsibility for the defense (including any settlements),
provided, however, that (a) the indemnifying party shall keep the indemnified
party informed of, and consult with the indemnified party in connection with,
the progress of any litigation or settlement, (b) the indemnified party shall
cooperate with the indemnifying party, at the indemnified party's expense, in
defending such claim, suit, expenses or the like; except that the indemnifying
party shall reimburse the indemnified party for any out-of-pocket expenses
resulting from cooperation specifically requested by the indemnifying party, and
(c) the indemnifying party shall not have the right, without the indemnified
party's consent, to settle any such claim if such settlement arises from or is
part of any criminal action, suit or proceeding or contains a stipulation or
admission or acknowledgment of any liability or wrongdoing (whether in contract,
tort or otherwise) on the part of the indemnified party or any of its
affiliates.

8.   OTHER PROVISIONS
     ----------------

8.1. Intellectual Property Ownership. As between the parties, CNC shall own and
     -------------------------------
retain all of its right, title and interest in the Virtual Private Network
Services and its Third Party Software, and all patent, copyright, trademark,
trade secret, and any other intellectual property rights thereto, and WNI shall
own and retain all of its right, title and interest in WebTV Services and its
Third Party Software, and all patent, copyright, trademark trade secret and any
other intellectual property rights thereto.

8.2. Confidentiality. The rights and obligations of the parties with respect to
     ---------------
confidentiality shall continue to be governed by the terms of that certain
Mutual Non-Disclosure Agreement between Artemis Research, Inc. (the predecessor
to WNI) and CNC dated as of April 2, 1996.
 

                                       9
<PAGE>
 
8.3. Representations And Warranties. Each party warrants that by entering into
     ------------------------------
this Agreement the party will not violate, conflict with or result in a material
default under any other contract, agreement, indenture, decree, judgment,
undertaking, conveyance, lien or encumbrance to which the party is a party or by
which it or any of its property is or may become subject or bound. Each party
shall not grant any rights under any future agreement, nor will it permit or
suffer any lien, obligation or encumbrances that will conflict with the full
enjoyment of either party of its rights under this Agreement. Each party further
represents and warrants that it has, and during the Term will have all necessary
rights, licenses, permits, governmental authorizations and the like to carry out
its obligations under this Agreement; and that it is in compliance with, and
during the Term continue to comply with, all material governmental laws,
regulations, orders and the like applicable to its provision of the services
contemplated by this Agreement.

8.4. Nonrestrictive Relationship: Nothing in this Agreement shall prevent CNC
     ---------------------------
from providing Virtual Private Network Services to other on-line services.
Nothing in this Agreement shall prevent WNI from engaging other network service
providers to provide services similar to those provided by CNC under this
Agreement.

8.5. LIMITATION OF LIABILITY. IN ANY ACTIONS ARISING FROM THE ALLEGED BREACH OF
     -----------------------
THIS AGREEMENT, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR SPECIAL,
INCIDENTAL, CONSEQUENTIAL OR PUNITIVE DAMAGES OF ANY NATURE, FOR ANY REASON,
INCLUDING WITHOUT LIMITATION THE BREACH OF THIS AGREEMENT OR ANY TERMINATION OF
THIS AGREEMENT, WHETHER SUCH LIABILITY IS ASSERTED ON THE BASIS OF CONTRACT,
TORT (INCLUDING NEGLIGENCE OR STRICT LIABILITY) OR OTHERWISE, EVEN IF THE OTHER
PARTY HAS BEEN WARNED OF THE POSSIBILITY OF SUCH DAMAGES.

8.6. Force Majeure: Neither party shall be deemed in default or liable under
     -------------
this Agreement, nor shall it hold the other party responsible for, any
cessation, interruption, delay or failure in the performance of its obligations
hereunder, except for any payment obligations, due to circumstances beyond its
reasonable control, including but not limited to earthquake, flood, fire, storm
or other natural disaster, epidemic, accident, explosion, casualty, act of God,
lockout, strike, labor controversy or threat thereof, riot, insurrection, civil
disturbance or commotion, boycott, disruption of the public markets, war or
armed conflict (whether or not officially declared), sabotage, act of a public
enemy, embargo, delay of a common carrier or any change in or the adoption of
any law, ordinance, rule, regulation, order, judgment or decree, provided that
the party relying upon this Section 8.7 shall have given the other party written
notice thereof promptly and in any event within fifteen (15) days after
discovery thereof and (b) shall take all steps reasonably necessary under the
circumstances to mitigate the effects of the force majeure upon which such
notice is based.

                                       10
<PAGE>
 
8.7.  Non-Assignment. This agreement shall be binding upon, and inure to the
      --------------
benefit of, the parties hereto and their respective successors and assigns.
Notwithstanding the above, neither party may assign this Agreement or any rights
or obligations under this Agreement without the prior written consent of the
other party, except that either party may assign this Agreement, and its rights
and obligations hereunder, to any entity that agrees in writing to be bound by
the terms and conditions of this Agreement, and succeeds to substantially all of
such party's assets or business in connection with a merger, reorganization or
sale or transfer of, unless such entity is a competitor of the other party. For
clarity, the parties acknowledge that WNI has entered into an definitive
agreement with Microsoft Corporation ("MS") and certain shareholders of WNI
which provides for a recapitalization of WNI and related transactions such that,
subject to certain conditions, WNI will become a subsidiary of MS; and that same
shall not violate this Agreement.

8.8.  Independent Contractors.  The parties shall have the status of 
      -----------------------
independent contractors, and nothing in this Agreement shall be deemed to place
the parties in the relationship of employer-employee, principal-agent, or
partners or joint ventures.

8.9.  DISCLAIMER. EXCEPT AS IS EXPRESSLY SET FORTH HEREIN, EACH PARTY DISCLAIMS
      ----------
ANY WARRANTY, EXPRESS OR IMPLIED, WITH RESPECT TO THE SOFTWARE OR SERVICES IT
SHALL PROVIDE PURSUANT TO THIS AGREEMENT, INCLUDING BUT NOT LIMITED TO ANY
WARRANTY OF DESIGN, TITLE, MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR
NON-INFRINGEMENT, EVEN IF SUCH PARTY HAS BEEN INFORMED OF SUCH PURPOSE. EACH
PARTY ALSO DISCLAIMS ANY WARRANTY THAT SUCH SOFTWARE OR SERVICE SHALL BE WITHOUT
INTERRUPTION OR ERROR-FREE.

8.10. Payment Terms.  Unless otherwise set forth in this Agreement, terms 
      -------------
for all payments are net thirty (30) days.

8.11. Non-Waiver.  Failure of either party to enforce any of its rights
      ----------
hereunder shall not be deemed to constitute a waiver of its future enforcement
of such rights or any other rights.

8.12. Severability. If any provision of this Agreement is held to be invalid,
      ------------
illegal, or unenforceable under present or future laws, such item shall be
struck from this Agreement; however, such invalidity or enforceability shall not
affect the remaining provisions or conditions of this Agreement. The parties
shall remain legally bound by the remaining terms of this Agreement, and shall
strive to reform this Agreement in a manner consistent with the original intent
of the parties.

                                       11
<PAGE>
 
8.13. Governing Law.  This Agreement shall be deemed to have been made in 
      -------------
the State of California, and the provisions and conditions of this Agreement
shall be governed by and interpreted in accordance with the substantive laws of
the State of California, without regard to conflict of laws provisions.

8.14. Arbitration. Any dispute or claim arising out of or in connection with
      -----------
this Agreement or the performance, breach or termination thereof, shall be
finally settled by binding arbitration in San Jose, California under the Rules
of Arbitration of the American Arbitration Association by an arbitrator
appointed in accordance with those rules. Judgment on the award rendered by the
arbitrators may be entered in any court having jurisdiction thereof.
Notwithstanding the foregoing, either party may apply to any court of competent
jurisdiction for injunctive relief without breach of this arbitration provision.

8.15. Integration. This Agreement expresses the complete and final understanding
      -----------
of the parties with respect to the subject matter hereof, and supersedes all
prior communications between the parties, whether written or oral with respect
to the subject matter hereof. No modification of this Agreement shall be binding
upon the parties hereto, unless evidenced by a writing duly signed by authorized
representatives of the respective parties hereto. For avoidance of doubt, the
Virtual Private Network Services Agreement dated August 16, 1996, and as amended
on December 1, 1996 and January 7, 1997, shall govern the provision of Virtual
Private Network Services until the Effective Date of this Agreement, and this
Agreement shall govern thereafter.

8.16. Notices. Any required notices hereunder shall be given in writing by
      -------
certified mail or overnight express delivery service (such as DHL) at the
address of each party below, or to such other address as either party may from
time to time substitute by written notice. Notice shall be deemed served when
delivered or, if delivery is not accomplished by reason or some fault of the
addressee, when tendered.

                                       12
<PAGE>
 
                                    If to CNC:
                                    Concentric Network Corporation, Inc.
                                    North Tantau Ave.
                                    Cupertino, CA 95014
                                    Attn.:  John Peters

                                    If to WebTV Networks, Inc.:
                                    Alma Street
                                    Palo Alto, CA 94301
                                    Attn.:  William Yundt


IN WITNESS WHEREOF, the duly authorized representatives of each of the
      parties hereto have executed this Agreement as of the Effective Date.


CONCENTRIC NETWORK                        WEB TV NETWORKS, INC. CORPORATION
                                        
                                        
                                        
By: /s/ Michael F. Anthofer               By: /s/ William H. Yundt 
   ---------------------------------         ---------------------------------
(authorized signature)                    (authorized signature)              
                                                                              
                                                                              
Printed Name: Michael F. Anthofer         Printed Name: William H. Yundt
             -----------------------                   -----------------------
                                                                              
Title: SUP & CFO                          Title: Vice President
      ------------------------------            ------------------------------ 

                                       13
<PAGE>
 
                                   EXHIBIT A
                                   ---------

Concentric Fees
- ---------------
As set forth in Section 5 of the Agreement.
 

Backbone and Internet Backup Fee During Term
- --------------------------------------------
[*], as set forth in Section 5 of the Agreement.
 

Prior to Transition Date
- ------------------------

<TABLE> 
<CAPTION> 
CNC Equipment                        [*]                       [*]
- ---------------------------------------------------------------------------
<S>                              <C>                           <C> 
[*] Router                            [*]                      [*]
Modems                                [*]                      [*]
[*] CSU/DSU                           [*]                      [*]
</TABLE> 

Post Transition Date:
- ---------------------

<TABLE> 
<CAPTION> 
CNC Equipment                         [*]                      [*]
- ---------------------------------------------------------------------------
<S>                               <C>                          <C> 
[*] Router                            [*]                      [*]
Modems                                [*]                      [*]
[*] CSU/DSU                           [*]                      [*]
</TABLE> 


                                 WNI Equipment
                                 -------------

Post Transition Date:
- ---------------------
[*]
Modems
[*] CSU/DSU


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

                                       14
<PAGE>
 
                                    Exhibit B
                                    ---------
                          Dedicated Access Line Pricing
                          -----------------------------

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions. A total of 2 pages has been 
omitted from this exhibit.


                                       15
<PAGE>
 
Additional explanations:

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions. A total of 2 pages has been 
omitted from this exhibit.


                                       16
<PAGE>
 
                               [GRAPHIC OMITTED]
 

                                       17
<PAGE>
 
                                   Exhibit C
                                   ---------
                         Network Escalation Procedures
                         -----------------------------

                     CNC Customer Support Operations Desk

                             Escalation Procedures

                                  Version 1.1

                                March 28, 1997


                               Table of Contents

<TABLE> 
<S>                                                                                               <C> 
Objective.........................................................................................19
Notification of Outage............................................................................19
        LEVEL I...................................................................................19
        LEVEL II..................................................................................19
        LEVEL III.................................................................................20
        LEVEL IV..................................................................................20
Problem Level Definitions and Escalation..........................................................21
        LEVEL I PROBLEM - Critical System Outage..................................................21
        LEVEL II PROBLEM - Critical System Service Degradation/Non Redundant Server Failure.......21
        LEVEL III PROBLEM - POP Site Outage.......................................................22
        LEVEL IV PROBLEM - POP Site Service Degradation...........................................22
Vendor Identified Problems........................................................................22
Concentric Problem Solving Procedures.............................................................23
        Operations Desk Staff Member..............................................................23
Contact List......................................................................................24
        Concentric Names and Numbers..............................................................24
        Vendor Names and Numbers..................................................................24
        Vendor Executive Staff....................................................................24
        Group E-mail Addresses....................................................................25
                 Group E-mail Notification to Vendor..............................................25
                 Group E-mail Notification to Concentric..........................................25
                 Emergency E-mail address.........................................................25
</TABLE> 

                                       18
<PAGE>
 
Objective:

The objective of this document is to describe the escalation procedures to be
used by Concentric Network Corporation (CNC) to notify WebTV of a problem with
CNC's network based on severity. Additionally, this document is to describe the
escalation procedure to be utilized when WebTV has identified a potential
problem with the CNC Network.

Notification of Outage:

CNC Customer Support Operations Desk will use the following methods to notify
WebTV for each level as described below. For Level I and Level II problems, CNC
will attempt to contact each person presented until live contact* is established
with each one.

* Either party may change designated contact information upon notice to the
other party.

LEVEL I:

For level I outages CNC operations desk will send e-mail to [*] Additionally,
CNC will make live contact with each person/group on the list.

[*]


LEVEL II:

For Level II outages CNC operations desk will send e-mail to [*].
Additionally, CNC will make live contact with each person/group on the list.

[*]

- -------------
* Definition of Live Contact: CNC Operations Desk Representative will; call
office # and leave voice mail if unanswered; call home # and leave message if
unavailable; call pager or cell phone. In order for live contact to be
successful the Operations Desk Representative must speak with the person/group
on the escalation procedure. If an attempt at live contact is unsuccessful the
Operations Desk will attempt contact 2 times per notification cycle ( i.e. Level
I, Operations Desk will call twice every hour until live contact is successful).
Note: We will attempt live contact 24 hours a day 7 days a week until successful
if the escalation procedure calls for it.

 
[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       19
<PAGE>
 
Level III:

For Level III outages CNC operations desk will send e-mail to [*].
Additionally, CNC will make live contact with each person/group on the list.

[*]

Level IV:

For Level IV outages CNC operations desk will send e-mail to [*] and/or to the
persons/groups specified below.

[*]

WebTV will use the following name and means to notify CNC of potential problems:

                                     [*]

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                     20
<PAGE>
 
Problem Level Definitions and Escalation

This section will describe the notification that will occur with CNC based
problems on the level (I. II. III, IV) of the problem identified.

Level I Problem-Critical System Outage

Data Center Equipment/Software: BCN Routers; Domain Name Servers; FDDI LAN;
Internet Access; AAA Servers; Login Servers; Public Network

 .    Within 15 minutes - Notify Director of NCC & Customer Services; and WebTV.
     Provide WebTV with status reports every 60 minutes thereafter (live
     contact) until problems are resolved.

 .    After 30 minutes - Notify VP Network Operations (CNC) with status reports
     every 30 minutes until problems are resolved.

 .    After 60 minutes - Notify President Network Services (CNC) with status
     reports every 30 minutes until problems are resolved.


LEVEL II PROBLEM - Critical System Service Degradation/Non Redundant Server
Failure

Data Center Equipment/Software: BCN Routers; Domain Name Servers; FDDI LAN;
Internet Access; AAA Servers; Login Servers; Public Network; Mail Servers, IRC
Server, Game Server, FTP Server, Web Server

 .    After 30 minutes - Notify Director of NCC & Customer Services (CNC), and
     WebTV. Provide WebTV with status reports every 60 minutes thereafter until
     problems are resolved.

 .    After 60 minutes - Notify VP Operations (CNC) with status reports every 60
     minutes until problems are resolved.

 .    After 120 minutes - Notify President Network Services with status reports
     every 60 minutes until problems are resolved.

                                       21
<PAGE>
 
LEVEL III PROBLEM - POP Site Outage

POP Equipment:  Modems; Terminal Servers; Routers; CSU/DSU; LEC network

 .    After 30 minutes - Notify WebTV, with status reports every two hours until
     problems are resolved

 .    After 4 hours - Notify Director NCC & Customer Services and update with
     status reports every 60 minutes until problems are resolved

 .    After 6 hours - Notify VP Network Services with status reports every two
     hours until problems are resolved


LEVEL IV PROBLEM - POP Site Service Degradation

POP Equipment:  Modems; Terminal Servers; Routers; CSU/DSU; LEC network

 .    After 2 hours - Notify WebTV, with status reports every four hours until
     problems are resolved



WebTV Identified Problems

WebTV will initiate a call to the Concentric Network Corporation's Operations
Desk at the number identified with in the contact list. The Operations Desk
representative will begin the process described in the section entitled
"Concentric Problem Solving Procedures". Based on the level of problem
determined, WebTV will be updated as described in the section "Problem Level
Definitions and Escalation".

                                       22
<PAGE>
 
Concentric Problem Solving Procedures


Operations Desk Staff Member:

1.    Receives notification of problem from WebTV.

2.    Obtains information from the WebTV contact describing the nature of the
      problem, affected POP sites, any noticeable network impacts, and any 
      other information the contact is able to provide regarding the nature of
      the problem.

3.    Evaluates the problem and assigns a level (I, II, III, IV).

4.    Informs the WebTV contact of the level assigned.

5.    Notifies and provides appropriate departments with all documentation 
      based on problem level assigned.

6.    Initiates Customer Notification Procedures per Priority Customer Contact
      Program Guidelines.

7.    Follows up to ensure resolution is accomplished.

8.    Unresolved problems are escalated within Customer Support and to 
      Technical Support Management based on problem type and priority level.

                                       23
<PAGE>
 
Contact List

Concentric Names and Numbers

<TABLE> 
<CAPTION> 
Name                                                   Phone                          Pager
- ------------------------------------------------------------------------------------------------------------
<S>                                                <C>                            <C> 

[*]

</TABLE> 

WebTV Names and Numbers

[*]


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       24
<PAGE>
 
Group E-mail Addresses

Group E-mail Notification to WebTV:

[*]

All communications regarding the operational status of the WebTV service should
be directed first to the WebTV Service Operations Center.
This organization is staffed [*].

Emergency email address

This email address is used to send outgoing mail by the Concentric Network
operations desk only in the event of a system wide failure:
                ----

[*]

Note:  Please do not send email to this address.
- ----

Either party may change any designated contact information upon notice to the
other.


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       25
<PAGE>
 
                                   Exhibit D
                           DAF Escalation Procedures

                          DEDICATED ACCESS FACILITIES
                             ESCALATION PROCEDURES

                                  Version 1.1
                                March 28, 1997


OBJECTIVE

The objective of this plan is to provide procedures for Concentric Network and
Dedicated Access Facility's (DAF) customers in the event of a system situation
specific to the DAF customer.

DEFINITION / CRITERIA

A system situation that warrants escalation to the DAF customer will be defined
as latency in excess of 150 milliseconds specific to the customer's dedicated
circuit, performance deviations that are atypical for the circuit, or outages
specific to the customer's dedicated circuit.

PROCEDURES

Note: If customer contact is not available (i.e. customer's operating hours),
technicians will leave a message where possible with a request to contact
Concentric Network's Customer Relations Operations desk.


 .   In the event of a situation that meets the criteria for escalation;
    Concentric Network technicians will contact the customer to ascertain if the
    outage is a result of customer initiated configuration changes, maintenance,
    etc.

           a.    Contact primary customer contact, if no response after 5
                 minutes
           b.    Contact secondary customer contact, if no response escalation
                 may be halted.

 .   If Concentric Network is not able to interface with the customer to
    eliminate customer initiated action as the cause of the situation,
    Concentric Network may:

           a.    Continue with internal escalation if initial trouble shooting
                 indicates the outage is associated with Concentric Network's
                 system.

           b.    Halt escalation (until 8 am EST next business day) if trouble
                 shooting indicates the customer's equipment may be the root
                 cause of the situation.

 .   If the situation is not customer initiated, Concentric Network will open a
    trouble ticket and begin diagnosis on CPE (Customer Premises Equipment) vs.
    network failure. If situation is isolated to CPE, Concentric will assist
    customer in configuration, as needed.

                                       26
<PAGE>
 
1.    Within 15 minutes after situation evaluation has eliminated customer
      initiated or Concentric Network specific situations. Concentric Network
      will initiate a trouble ticket call to Vendor (LEC/Inter-Exchange Carrier,
      leased line, etc.), update the customer when possible, record vendor
      trouble ticket number, and log all developments.

2.    Within 30 minutes after situation evaluation Concentric Network will
      request vendor to escalate internally to manager or duty supervisor. If
      vendor has isolated the trouble and has ascertained ETR (Estimated Time of
      Repair) is within 2 hours, Concentric Network may halt escalation. If root
      cause is still undetected or if ETR is greater than 2 hours, then
      escalation will proceed to next step.

3.    Within 1 hour, if root cause is not yet determined, escalate to Customer
      Support Team leader and Network Operations Supervisor or manager on duty.
      The Network Operations Supervisor will escalate to vendor such as the
      service manager.

4.    Concentric Network will conduct hourly updates until a definitive ETR is
      established within a 2-hour window. If the ETR is not within a 2-hour
      window, Concentric will consult with the DAF customer to establish a
      mutually agreeable update plan.

Upon service restoration, Concentric Network will notify the DAF customer, with
an update and post-mortem analysis.

If outage is escalated to Customer Relations management, an outage notification
will be provided to the appropriate Sales manager and Upper Management that
explains the outage duration and analysis.

                                       27
<PAGE>
 
8.16.1.1.  DAF Customer Contact Information

Concentric Network will use the information provided below for contacting DAF
customers. Customers may list an alternate for contacting in the event;
Concentric is unable to contact the primary contact. More information on contact
methodology and customer preferred methods of contact are on the following page.

[*]
 
[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       28
<PAGE>
 
Contact Methods

H = Home Phone                   AH = Alternate's Home Phone 
W = Work Phone                   AW = Alternate's Work Phone 
M = Mobile Phone                 AM = Alternate's Mobile Phone 
P = Pager                        AP = Alternate's Pager 
E = Email                        AE = Alternate's Email  
NA = Not available for contact 

Please indicate as shown, the days and time when you will be available for
contact by Concentric Network Customer Relations operations desk. Please
indicate by the Contact Methods shown

<TABLE> 
<CAPTION> 
Example
- ---------------------- ---------------- ---------------
Time / Day             Sunday           Monday
- ---------------------- ---------------- ---------------
<S>                    <C>              <C>   
12 - 1 am              H                P
- ---------------------- ---------------- ---------------
1 - 2 am               NA               NA
- ---------------------- ---------------- ---------------

<CAPTION> 
Time in Eastern Time Zone
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
Time/Day          Sunday       Monday      Tuesday      Wednesday    Thursday      Friday      Saturday
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
<S>               <C>          <C>         <C>          <C>          <C>           <C>         <C>  
12 - 1 am         AP           AP          AP           AP           AP            AP          AP
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
1 - 2             AP           AP          AP           AP           AP            AP          AP
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
2 - 3             AP           AP          AP           AP           AP            AP          AP
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
3 - 4             AP           AP          AP           AP           AP            AP          AP
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
4 - 5             AP           AP          AP           AP           AP            AP          AP
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
5 - 6             AP           AP          AP           AP           AP            AP          AP
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
6 - 7             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
7 - 8             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
8 - 9             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
9 - 10            H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
10 - 11           H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
11 - 12 pm        H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
12 - 1            H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
1 - 2             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
2 - 3             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
3 - 4             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
4 - 5             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
5 - 6             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
6 - 7             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
7 - 8             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
8 - 9             H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
9 - 10            H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
10 - 11           H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
11 - 12           H W E        H W E       H W E        H W E        H W E         H W E       H W E
- ----------------- ------------ ----------- ------------ ------------ ------------- ----------- ------------
</TABLE> 

The Direct Access Customer will use the following name and means to notify
Concentric Network of potential problems:

           Contact Point: Customer Relations Operations Desk
           E-mail address: [*]
           Phone Number:  [*]
* Either party may change designated contact information upon notice to the
other party.

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       29

<PAGE>
 
                                                                   EXHIBIT 10.38


                        CO-MARKETING SERVICES AGREEMENT

This Co-Marketing Services Agreement ("AGREEMENT"), entered into by and between
Netscape Communications Corporation ("NETSCAPE"), a Delaware corporation located
at 501 East Middlefield Road, Mountain View, California 94043, and Concentric
Network Corporation ("CONCENTRIC"), a Florida corporation with its principal
place of business at 10590 N. Tantau Avenue, Cupertino, California 95014 is
effective as of the effective date set forth below ("EFFECTIVE DATE").

                                    RECITALS

A. Netscape is in the business of developing, manufacturing, marketing and
   distributing Internet-related products and technology, provides related
   services, and in connection with its marketing efforts, maintains World Wide
   Web ("WEB") sites for the provision of local-language geographically-targeted
   Internet content, navigation and directory services;

B. Concentric is in the business of offering certain Internet and Intranet-
   related services;

C. Netscape is implementing offerings to provide hosted applications to
   customers; such hosted applications will be a co-branded Service (as defined
   below) that allows individual professionals, small businesses and project-
   based users to quickly, easily, and economically run an Intranet for their
   business;  and

D. The parties wish to enter into this Agreement to specify the terms and
   conditions of their development,  implementation,  co-marketing, and support
   of the Service.

NOW, THEREFORE, in consideration of the mutual covenants contained herein, the
parties agree as follows:

1.   DEFINITIONS.

For purposes of this Agreement, in addition to the capitalized terms defined
elsewhere in this Agreement, the following terms shall have the meanings set
forth below:

"APPLICATIONS" means the Intranet applications that will be provided to
Customers via the Service.  Applications will include:  web publishing, email,
private discussion groups operated by Customers, directory, and document
publishing, collaboration, and management.  Additional applications may include,
but are not limited to:  calendering, conferencing, HR handbooks, accounting and
financial, timesheet tracking and billing, sales automation, and job postings.

"CO-BRANDED" means bearing the Service Name.

"CONCENTRIC BRAND SERVICE" means the service described as "Concentric Brand
Service" in Exhibit A.
            --------- 
"CONCENTRIC WEB SITE" means the Concentric Web site specified in Exhibit A.
                                                                 --------- 

"CUSTOMER" means an individual, sole proprietorship, partnership, corporation,
or other legal entity that registers for the Service in accordance with the
terms and conditions of this Agreement.
<PAGE>
 
"NETSCAPE'S WEB SITE" means the collection of HTML documents accessible by the
public via the Internet at the URL listed on Exhibit B and/or at such other URL
                                             ---------
or URLs as Netscape may designate. For purposes of this Agreement, Netscape's
Web Site shall include, without limitation, the Netscape Services Home Page.

"NETSCAPE'S HOME PAGE" means the home page of Netscape's Web Site.

"NETSCAPE SERVICES HOME PAGE" means the first page that is linked to from
Netscape's Web Site when an end user clicks on the button described in Section
3.1.

"PAYMENT" means the amount specified as "Payment" on Exhibit C.
                                                     --------- 

"SERVICE" means a hosted applications service offered to customers that will:
(a) allow individual professionals and small businesses to quickly, easily, and
economically establish and run an intranet; and (b) use Netscape SuiteSpot
software features.  The Service will be Co-Branded by Netscape and Concentric
pursuant to this Agreement.  For purposes of this Agreement, the Netscape
Services Home Page will not be deemed a part of the Service.

"SERVICE AD INVENTORY" means the electronic advertising inventory within the
Service.

"SERVICE LAUNCH DATE" means the first date on which the Service is fully
functional and accessible to Customers, as described in this Agreement.

"SERVICE NAME" means:  (i) the name initially agreed to by the parties for
purposes of co-branding the Service; and (ii) any replacement name(s) determined
by mutual agreement of the parties.

"TERM" means the period specified as "Term" on Exhibit A.
                                               --------- 
"THIRD PARTY PROVIDER" means a company that provides applications for use by
Customers in the Service.

2.   TERRITORY.  The geographic scope of this Agreement is intended to be the
U.S. and English-speaking Canada ("Territory").  To the extent that the Service
                                   ---------                                   
may be used by Customers outside of the Territory, such use will also be subject
to the terms and conditions of this Agreement.

3.   SERVICE FEATURES.  The Service shall conform with the following 
requirements:

     3.1. Netscape's Home Page.  A menu item, with a name chosen by Netscape,
          --------------------                                               
will appear above the fold on Netscape's Home Page no later than the Service
Launch Date and for the remainder of the Term.  When the button corresponding to
such menu item is selected by an end user, the end user will be linked to the
Netscape Services Home Page.

     3.2. Netscape Services Home Page.
          --------------------------- 

          (a) The Netscape Services Home Page will:  (i) be designed, developed,
produced and managed by Netscape, including but not limited to hiring and
managing creative and technical staff as needed to do so; (ii) be hosted and
maintained solely on Netscapes's servers; (iii) have a dedicated [*] (or such
other [*] as Netscape may determine); and (iv) be directly linked, [*], from
Netscape's Home Page. The parties acknowledge and agree that all access to the
Netscape Services Home Page shall be deemed to be via Netscape's Web Site, and
therefore [*]. The parties acknowledge that it is their intent that the
principal function of the Netscape Services Home Page will be to drive traffic
to, and generate subscribers for, the Service.

          (b) On the Netscape Services Home Page, links to and information about
the Service will be accorded the majority of the [*] screen space. Within such
majority of such [*] screen space, there will be a link to Concentric's
enterprise access service, subject to the terms and conditions of this
Agreement. The remainder of such useable screen space will be the sole
responsibility of Netscape and will not be subject to the terms and conditions
of this Agreement.

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       2
<PAGE>
 
     3.3. Service Pages.
          ------------- 

          (a) The Service will:  (i) be produced and managed by Concentric,
including but not limited to hiring and managing creative, technical, customer
support, and general staff as needed to do so; (ii) be hosted and maintained
solely on [*]; and (iii) have a [*] (such as [*] or such other [*] as Netscape
may determine).

          (b) Concentric and Netscape will mutually agree to the design and look
and feel of the Service and its Web pages.  Netscape will be responsible for
assisting Concentric with the navigational and architectural structure for
displaying the contents of the Service's Web pages (i.e., text and graphical
elements).  At Netscape's expense, Netscape will provide the services of a
producer to assist with the design of the Service's Web pages.

          (c) Every page of the Service will be Co-Branded above the fold.

     3.4. Purchase, Implementation, Maintenance And Support. Subject to the
          --------------------------------------------------               
provisions of Exhibit C, Concentric expressly agrees that Concentric shall be
              ---------                                                      
solely responsible for the purchase, implementation, maintenance and support of
all software and hardware required to fulfill its obligations under this
Agreement.

     3.5. Target Market.  The Service's primary target market is as specified as
          -------------                                                         
"Target Market" on Exhibit A.
                   --------- 

     3.6. Name of the Service.  The initial Service Name, and any subsequent
          -------------------                                               
Service Names, will be mutually agreed upon by Netscape and Concentric.
Concentric shall not independently use the Service Names without Netscape's
prior written consent unless such use occurs in connection with Concentric's
advertising sales and promotional efforts on behalf of the Service in accordance
with this Agreement.  The Service Name shall be displayed on every page of the
Service and on no other locations without Netscape's prior written consent
except in connection with such advertising sales and promotional efforts on
behalf of such Service.  If a Service Name includes a co-branding component,
Concentric may not use the corresponding Service Name with Netscape's name
expunged.  Concentric may not use a Service Name independent of the Service
except as provided for above in this Section 3.6.

     3.7. Design of Service.  The Service shall be co-branded equally by
          -----------------                                             
Netscape and Concentric.  Netscape shall be responsible for creating, and
Concentric shall be responsible for implementing, the graphic user interface
including navigation, architecture, look and feel as well as the tone of the
Service, taking into consideration the cultural, economic and linguistic
qualities of such Service's Territory;  provided, however, that Netscape and
Concentric shall mutually agree to the initial design, and each subsequent
design, of the Service.

     3.8. Netscape Products.
          ----------------- 

          (a) Except as specified in subsection (b) below, Netscape does not
grant to Concentric under this Agreement any right or license to use any
trademarks, content, products or other technology.

          (b) Subject to the terms and conditions of this Agreement, Netscape
hereby grants to Concentric a non-exclusive, non-transferable license for the
Term to implement, utilize, and display to Customers and their end users within
the Service, all of Netscape's Design Contributions.  "NETSCAPE'S DESIGN
CONTRIBUTIONS" means Netscape's contributions under this Agreement to the look
and feel and overall design of the Service.   Upon the expiration or termination
of this Agreement, Concentric will immediately discontinue all of its use of
Netscape's Design Contributions, except as may be expressly permitted by this
Agreement.

     3.9. Roll-out Schedule.   The parties will use their reasonable best
          -----------------                                              
efforts to meet the phased roll-out requirements for the Service as specified in
                                                                                
Exhibit  D.
- ---------- 

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       3
<PAGE>
 
     3.10.  Customer Registration.   Each Customer will register for the Service
            ---------------------                                               
in accordance with Exhibit E.  Any and all information regarding each Customer
                   ---------                                                  
and its end users that is obtained by Concentric through, or in connection with,
the Service will be subject to the terms and conditions of Exhibit E.
                                                           ---------- 

     3.11.  Separate Servers.   Concentric agrees that, beginning no later than
            ----------------                                                   
January 1, 1998, the primary functions and applications of the Service will be
run on dedicated hardware servers throughout the remainder of the Term.

     3.12.  Technical Support.   During the Term:
            -----------------                    

          (a) Concentric shall provide technical support services for the
Service to Netscape on a timely basis, appoint a technical contact to whom
Netscape may address all technical questions relating to the Service, and use
its reasonable commercial efforts to promptly remedy any material misplacement
or malfunctioning of the Service; provided, however, that Concentric will
provide the foregoing no less effectively and timely than it provides such
services in connection with other Concentric services.

          (b) Concentric shall be responsible for each Customer's maintenance
and support requirements in connection with the Service, which will be mutually
agreed to by Netscape and Concentric in the form of written maintenance and
support guidelines.  In Concentric's performance of such obligations, the
Customers shall not be disadvantaged or suffer from inferior performance
relative to the customers of the Concentric Brand Service and other Concentric
Internet offerings.

          (c) Concentric will provide front line support to the Third Party
Providers. If Concentric receives any questions from a prospective or existing
Third Party Provider relating to specific development or technical support (such
as how to develop on the Netscape platform), Concentric will refer the
prospective or existing Third Party Provider to the Netscape Developer Program
as described on Netscape's Web Site.

          (d) Concentric will provide Netscape at no charge with two (2) test
accounts that will permit Netscape to access and test the functionality of the
Service at any  time during the Term.

4.   REPORTS.

     4.1. Search Field.  A field providing search functionality may be included
          ------------                                                         
on pages within the Service as the parties may mutually determine.  The search
executed from the search field will initially only cover content within such
search field's Service itself.  When the results to a search query are returned,
a user may be given the option of expanding the scope of the search to
encompass the World Wide Web using one of [*] search engines as appropriate
for the Territory. The user will also be offered the choice of executing
another search limited to the content of such Service. The terms and
conditions of this paragraph will not apply to pages created solely by
Customers without the assistance of the Service.

     4.2. Search Field Positioning. The search field described in Section 4.1
          ------------------------                                           
shall appear below the fold on any page in which the search field is listed.
The search engine companies which appear as expanded search options, as well as
the positioning of the search engine companies on the page served to end users
in conjunction with the end user's search results, are subject to Netscape's
approval. Concentric shall not charge any of the search engine companies for
these listings. Netscape reserves the right to review the [*] search field in
the Service as such search functionality may impact [*], and require that the
search functionality in any or all Service be [*] or [*].

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.



                                       4
<PAGE>
 
     4.3. Monthly Search Reports. Within fifteen (15) days of the end of each
          ----------------------                                             
month during the Term, Concentric shall provide Netscape with monthly reports
detailing the following information for each day during the month covered in the
report:

   . any information collected in the course of operating the Service about 
     [*] that Concentric collects whether such information is [*] or
     technology-provided.

The parties shall mutually determine the format and the date of submission for
this monthly report.  The information contained in each report shall be
Netscape's and Concentric's Confidential Information.

     4.4. Weekly Log Reports.  On a weekly basis, Concentric shall provide
          ------------------                                              
Netscape with the daily [*] logs for the Service. The information contained in
the report shall be Netscape's and Concentric's Confidential Information,
provided, however that Netscape shall have the right to use the information
contained in such reports in Netscape's private and public reporting of access
to (i) the Service in the aggregate, (ii) Netscape's Web Site, individually
and in the aggregate, and (iii) Netscape's web sites worldwide in the
aggregate.

5.   APPLICATIONS  FOR THE SERVICE.

     5.1. Selection of Applications.  Applications and content for the Service
          -------------------------                                           
will be as mutually agreed to by Netscape and Concentric in writing from time to
time.

     5.2. Concentric and Netscape Applications.  Any and all Applications
          ------------------------------------                           
provided by Concentric or Netscape for the Service will be accounted for solely
in accordance with Exhibit C.
                   --------- 

     5.3. Third Party Provider Applications.  To the extent that Netscape and
          ---------------------------------                                  
Concentric mutually agree that  any applications for the Service are to be
supplied by a Third Party Provider:  (a)  such third party will be compensated
as mutually agreed by Netscape and Concentric; and (b) Netscape will not be
excluded from, or denied any right with respect to, such third party or its
Applications.  Such third party will supply such applications pursuant to an
agreement between such third party and Concentric containing terms and
conditions, and in a form, mutually agreed by Netscape and Concentric, including
at a minimum the following:  (i) the Third Party Provider will fully indemnify
Concentric and Netscape against any  third party claims arising from content
posted, displayed, or transmitted on the Service by Customer or its end users;
(ii) any and all liability of Netscape in connection with such agreement will be
disclaimed; and (iii) Netscape will be specified as a third party beneficiary of
such agreement.

     5.4. Customer's Selection of Applications.  During the registration process
          ------------------------------------                                  
or thereafter, each Customer shall electronically specify which applications it
wishes to utilize in the Service.  Concentric will be responsible for
configuring and maintaining each Customer's use of the Service in accordance
with Customer's requests to Concentric.

     5.5. Integrated Community.  Netscape and Concentric acknowledge that the
          --------------------                                               
intent of the Service is to provide an "integrated community" experience for end
users and not to provide Concentric with any [*] in listings
relative to any other Third Party Provider, unless such [*] is agreed to by
Netscape. Promotion of Concentric's web sites and Internet-related services
will be minimized to prevent diversion of user traffic from the Service.
Promotion of Concentric within a Service will be subject to Netscape's
approval.

6.   MARKETING.

     6.1. Netscape's Marketing.  During the Term, 
          --------------------                                                  
[*] which is: (i) a intranet applications hosting service, (ii) [*], (iii) [*]
to (within

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       5
<PAGE>
 
[*] from) the then-current home page of Netscape's U.S. English-language Web
site, and (iv) is operated in the English language.

     6.2. Concentric's Marketing. During the Term, and 
          ----------------------                                              
[*] adequately focused on developing and maintaining the Service, Concentric
[*] which is: (i) a [*], (ii) [*] users, and (iii) is operated in the English
language. Notwithstanding the foregoing, [*] as a [*] service until [*].

7.   CONCENTRIC'S OBLIGATIONS.
 
     7.1. Production, Technology and Content Programming.
          ---------------------------------------------- 

          (a) Concentric shall be responsible for all hosting, production, and
programming of the Service, consistent with each Customer's specifications. The
Service shall not be [*] from [*] production, programming or performance [*].
The Service shall perform [*] standards as the Concentric Brand Service.
Concentric shall perform its duties described herein with [*] as it employs
with respect to its [*] and Web sites and the services and Web sites
Concentric may operate for third parties, and Concentric [*] own Web sites or
services, or those of any third party, [*] Service.

          (b) With respect to features and functionalities offered within the
Service, Concentric shall [*] a technology which might [*] Netscape products
or services (except for technologies developed by Concentric and not covered
elsewhere in this Agreement), unless Concentric has obtained Netscape's
written approval to use such a competing technology. Concentric will ensure
that all technologies and services provided by suppliers for the Service will
be compliant and compatible with Netscape technologies. Concentric will
optimize the Service to use Netscape's most current technologies, which will
be fully operational and available to Customers [*] of each new Netscape
client product, unless the parties mutually agree that the implementation of a
certain technology is not technically feasible for the Service.

          (c) Concentric's obligation to produce the Service, including without
limitation offering hosting, production services, technology and programming
which [*] established by Concentric on its own Web site or
services (or the Web site or services Concentric manages for any third party)
and [*], is a material obligation of Concentric under
this Agreement.

     7.2. Advertising.  Advertising and similar promotions within the Service
          -----------                                                        
will be designed by mutual agreement of Netscape and Concentric. Netscape will
manage and sell all advertising and sponsorships within the Service Ad
Inventory.  Netscape will manage the advertising product and services with the
[*] of professionalism Netscape exercises with respect to Netscape's own
Web sites.

     7.3. Harm to Netscape.
          ---------------- 

          (a) Netscape may, in its reasonable discretion, at any time [*]
or publish, or direct Concentric to refuse to accept or publish and [*]
publication of, a Third Party Provider application, an advertisement and/or
other content on the Service and any other areas related to the Service if
such content is, in Netscape's [*], including, without limitation, any
material that encourages conduct that would constitute a criminal offense,
give rise to civil liability, or otherwise violate any applicable local,
state, national or international law.

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       6
<PAGE>
 
          (b) If Netscape, in its [*], at any time determines that any of
Concentric's [*] and [*], including but not limited to the [*] contains or
presents any material that has been prepared by or for Concentric or a Third
Party Provider in a manner that Netscape [*] or an infringement of Netscape's or
a third party's rights, or unlawful in any country or territory, Netscape may
immediately terminate this Agreement if Concentric has not revised to Netscape's
reasonable satisfaction that material or presentation within three (3) business
days of notification by any means from Netscape.

          (c) If Netscape, in its [*], at any time determines that any of
Concentric's [*] and [*], including but not limited to the [*] contains any
material or presents any material (other than material within the scope of
subsection (b) above) in a manner that Netscape [*] or an infringement of
Netscape's or a third party's rights, or unlawful in any country or territory,
Netscape may immediately terminate this Agreement if Concentric has not revised
to Netscape's reasonable satisfaction that material or presentation within three
(3) business days of notification by any means from Netscape.

          (d) To the extent that, following a notification by Netscape to
Concentric pursuant to subsection (b) or (c) above, Concentric's good faith
actions undertaken in accordance with such notification result in a third party
affected by such actions initiating claims against Concentric for damage
allegedly caused by such actions of Concentric, then:

              (i)    if such actions were in connection with the Service,
Concentric's [*] paid in [*] such action will be treated as [*] of the Service
in accordance with Exhibit C;
                   ---------
or

              (ii)   if such actions were in connection with any [*] other 
than the Service, Concentric's [*] paid in [*] such action will 
[*] by Netscape;

provided that Concentric will (A) promptly notify Netscape in writing of any
such claim and (B) if such claim is under subsection (ii) above, Concentric will
grant Netscape control of the defense and all related settlement negotiations,
and will cooperate with Netscape, at Netscape's expense, in defending or
settling such claim.

          (e) Concentric will prepare, and propose to Netscape: (i) the initial
[*] that will govern the use of the Service by Customers and their end users;
and (ii) from time to time, appropriate modifications and additions to such [*]
Concentric and Netscape will [*] on such [*] and all material modifications and
additions thereto, prior to their implementation. Such [*] will govern each
Customer's, and its end users', use of the Service. Concentric will be
responsible for [*] in a manner [*] by Concentric and Netscape. Subject to
the terms and conditions hereof, Netscape and Concentric will reasonably [*]
against Customers or end users that [*] them.

     7.4. Netscape Now Program Compliance on Concentric's Web Site and the
Services.

          (a) Subject to the provisions of Section 8.6 Concentric shall display
the "Netscape Now" button [*] of the Services and on [*], on [*] Concentric's
Web site linked to the Service, and on [*] on any Concentric web site which
(except as provided under Section 8.6(c)) contains a (i) [*] or (ii) [*] or
(iii) [*] and use best efforts to include the following statement (or a
statement designated by Netscape and generally used by Netscape as a successor
to the following statement or in connection with any successor program to
Netscape's Netscape Now program) next to the Netscape Now button: "This site is
best viewed with Netscape

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.



                                       7
<PAGE>
 
Communicator. Download Netscape Now!" Concentric will produce each such page
such that when an end user presses or clicks on the Netscape Now button (or such
other button used in connection with any successor program to the Netscape Now
program), the end user's Internet client software will access the applicable
HTML page located at a URL supplied by Netscape. On any page on which the
Netscape Now button, or a successor button, is displayed, the Netscape Now
button shall be [*] and [*] the virtual [*] for any third party [*] or [*]
Concentric shall use reasonable commercial efforts promptly to remedy any
misplacement of the Netscape Now button on its home page or other pages or any
malfunctioning of the button, provided Netscape will fully cooperate with
Concentric to remedy any such misplacement or malfunctioning, and provided
further that Concentric shall not incur liability for any failure to remedy such
misplacement or malfunctioning if such remedy is not within the reasonable
control of Concentric. In the event that Netscape replaces the Netscape Now
program with a successor program, Netscape shall advise Concentric and
Concentric shall produce each such page to conform to such successor program,
provided Concentric's obligations under such successor program shall not be
materially increased. Netscape hereby grants Concentric a nonexclusive,
nontransferable, nonassignable, nonsublicensable, royalty-free license to
perform and display the Netscape Now button directly in connection with
fulfilling the foregoing obligation. Concentric's use of the Netscape Now button
shall be in accordance with Netscape's reasonable policies regarding advertising
and trademark usage as established from time to time by Netscape, including the
guidelines of the Netscape Now Program published on Netscape's U.S. English-
language Web Site. Concentric acknowledges that the Netscape Now button is a
proprietary logo of Netscape and contains Netscape's trademarks. In the event
that Netscape determines that Concentric's use of the Netscape Now button is
inconsistent with Netscape's quality standards, then Netscape shall have the
right to suspend immediately such use of the Netscape Now button. Concentric
understands and agrees that the use of the Netscape Now button in connection
with this Agreement shall not create any right, title or interest in or to the
use of the Netscape Now button or associated trademarks and that all such use
and goodwill associated with the Netscape Now button and associated trademarks
will inure to the benefit of Netscape. Concentric agrees not to register or use
any trademark that is similar to the Netscape Now button. Concentric further
agrees that it will not use the Netscape Now button in a misleading manner or
otherwise in a manner that could tend to reflect adversely on Netscape or its
products.

     7.5. Marketing Collateral.  Concentric will maintain on the Service readily
          --------------------                                                  
available on-line marketing collateral for the Service.  The collateral will be
updated on a timely and on an as-needed basis.

     7.6. Service Enrollment Support.  Concentric shall provide information and
          --------------------------                                           
application development support to Third Party Providers regarding participation
in the Service.

     7.7. Use of Netscape's Menu Applets. In addition, Concentric shall, at
          ------------------------------                                   
Netscape's request, implement user interface elements and interface applications
for the Service, provided that, in Concentric's reasonable judgment, such
implementation does not require extraordinary development efforts in the
operation of the Service.

8.   JOINT ACTIVITIES AND OWNERSHIP.

     8.1. Press Plans.  Concentric and Netscape agree to participate in a joint
          -----------                                                          
press announcement regarding the Service which will take place on a mutually
agreed upon date.  The parties shall agree to the form and content of the joint
press release.  Notwithstanding the foregoing, either party may issue its own
press release, subject to the other party's prior approval of the content within
the release; with respect to major advertising and marketing deal announcements
regarding the Service, Netscape and Concentric shall each use its reasonable
commercial efforts to respond to a request for such approval within forty-eight
(48) hours of its 


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       8
<PAGE>
 
receipt of a copy of the proposed announcement, provided that neither party will
in any event make any such announcement without first receiving the other
party's prior approval. In any press announcement regarding any or all of the
Service, both Concentric and Netscape's name and logo shall be included in the
press release, and the names and logos shall appear with equal prominence.
Interviews with the press regarding announcement of the Service shall be
coordinated between both Netscape and Concentric.

     8.2. Research.  If Concentric or Netscape conducts any research regarding
          --------                                                            
any or all of the Service, such research results shall be shared between both
companies on a timely basis.  If Concentric or Netscape conducts a study on
their respective Web sites, both companies shall include the Service in the
study, as appropriate.  Concentric will conduct substantially the same level and
as much research and data collection regarding the Service as Concentric
conducts with respect to the Concentric Brand Service and other Concentric
offerings.

     8.3. Quarterly Reviews of the Service.  Netscape and Concentric agree to
          --------------------------------                                   
establish quarterly reviews of the Service to evaluate the Service and agree to
modifications and improvements to the Service.

     8.4. Design Reviews and Ownership.
          ---------------------------- 

          (a) Design Review.  Netscape and Concentric shall mutually agree to
              -------------                                                  
all significant changes and enhancements to the look and feel of the Service,
including, but not limited to, significant new artwork or functional changes.

          (b) Look and Feel of Collective Work and Individual Contributions.
              -------------------------------------------------------------  
[*]  Notwithstanding the foregoing, the ownership rights of Concentric, each
Third Party Provider, and their respective licensors to the look and feel of any
and all contributions to such collective work shall not be diminished or
otherwise affected by Netscape's rights in such collective work.

          (c) Ownership of Other Copyrightable Subject Matter.  Copyrighted
              -----------------------------------------------              
elements contained in the Service shall be the property of the copyright owner.

          (d) Post-Termination License.  Concentric hereby grants to Netscape a
              ------------------------                                         
[*] without payment or other charge therefor, to use the [*] in association with
such Service or any future service after the termination or expiration of this
Agreement.

          (e) Independent Development.  Subject to the terms and conditions of
              -----------------------                                         
the Non-Disclosure Agreement attached hereto as Exhibit F, nothing contained
                                                ---------                   
herein shall prevent Netscape or Concentric from independently developing
features or functionality which are similar to the features and functionality
owned by the other party and implemented in the Service.

     8.5. Optimize for Netscape Technology.
          -------------------------------- 

          (a) Concentric will [*] to use Netscape's [*] Such [*] will be fully
operational and public [*] to the release of new Netscape client products,
unless both parties mutually agree that the implementation of a certain
technology is not technically feasible.

          (b) In order to [*] support of current Internet browser technologies,
Concentric shall implement a [*] Concentric's own Web sites implementing at
least one of the following: [*] or the then current [*] technology (or
subsequent features displayable by an end user's browser). Such features shall
be positioned [*] of the Service and within at least one [*] location on
Concentric's own Web site. The [*] shall be fully operational and publicly
accessible at the [*] client products.


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

                                       9
<PAGE>
 
     8.6. Netscape Software:  In order to [*] between Concentric and Netscape
          -----------------
and [*] of Netscape's products, Concentric agrees to [*] on an [*] basis.
This means that Netscape shall receive [*] to any other Internet client software
company, except as described below:

          (a) On Concentric's home page, such page currently being located at
http://www.concentric.net, or any successor home page which is Concentric's
primary web site referring to their service offerings, Netscape [*] will
include, but is not limited to, the Netscape logo or other promotional
elements, subject to the terms and conditions of Section 7.4.

          (b)  On Concentric's enterprise web site, or such page currently being
located at http://enterprise.concentric.net, or any successor web site which is
Concentric's primary web site offering services to their enterprise customers,
Netscape will receive [*] and positioning and such [*] client or server [*].
Such [*] and [*] will be subject to the terms and conditions of Section 7.4.

          (c)  Notwithstanding the foregoing, the parties acknowledge that with
regard to the [*] Concentric's Web site, such portion located at the URL
http://home.concentric.net, and solely with regard to the [*] Internet browser
client software, and only until the [*] between Concentric and any [*] Netscape
may [*] which is [*] than the [*] received by a third-party Internet [*]
provider.

     8.7. Advertising of the Service.  Netscape will promote the Service through
          --------------------------                                            
advertising placement on its site and other sites.

     8.8. InBox Direct.  Netscape will promote the Service within appropriate
          ------------                                                       
Netscape newsletters that it manages in the InBox Direct program.  Netscape will
provide, produce, and manage a Service newsletter with a premium position in
InBox Direct.

     8.9. Netscape Netcaster. Netscape will provide, produce, and manage a
          ------------------                                              
dedicated Service channel or a Service feature section within the Netscape
Channel.

     8.10.  Other Co-Marketing Activities.  In addition to activities set forth
            -----------------------------                                      
in this Section 8, the parties shall participate in other co-marketing
activities related to the Service and this Agreement as agreed to by the parties
from time to time.

9.   PAYMENT.

     9.1. Payment Amounts.  For the benefits and services provided by Netscape
          ---------------                                                     
to Concentric during the Term, Concentric shall remit to Netscape the Payments
of Applications Hosting Net Revenues as set forth on Exhibit C.  For the
                                                     ---------          
benefits and services provided by Concentric to Netscape during the Term,
Netscape shall remit to Concentric the Payments or Advertising Net Revenue as
set forth on Exhibit C.
             --------- 

     9.2. Timing of Payment. Each party shall make the Payments in accordance
          -----------------                                                  
with the schedule set forth on Exhibit C.
                               --------- 

     9.3. Currency, Interest and Taxes.  All amounts payable hereunder are
          ----------------------------                                    
denominated in U.S. Dollars, and all amounts payable to Netscape hereunder shall
be remitted in U.S. Dollars.  Any portion of any Payment which has not been paid
to Netscape within the applicable time set forth herein shall bear interest at
the lesser of (i) one percent (1%) per month, or (ii) the maximum


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       10
<PAGE>
 
amount allowed by law. All payments due hereunder are exclusive of any
applicable taxes. Concentric shall be responsible for all applicable national,
state and local taxes, value added or sales taxes, exchange, interest, banking,
collection and other charges and levies and assessments pertaining to payments,
other than U.S. taxes based on Netscape's net income. If Concentric is required
by law to make any deduction or to withhold from any sum payable to Netscape by
Concentric hereunder, (i) Concentric shall effect such deduction or withholding,
remit such amounts to the appropriate taxing authorities and promptly furnish
Netscape with tax receipts evidencing the payments of such amounts, and (ii) the
sum payable by Concentric upon which the deduction or withholding is based shall
be increased to the extent necessary to ensure that, after such deduction or
withholding, Netscape receives and retains, free from liability for such
deduction or withholding, a net amount equal to the amount Netscape would have
received and retained in the absence of such required deduction or withholding.

10.  CUSTOMER BILLING.  Concentric will be responsible for Customer billing.
Such billing must be Co-Branded no later than January 1, 1998 and throughout the
remainder of the Term; Concentric will use reasonable commercial efforts to
implement Co-Branded billing prior to such date.  All billing procedures and
requirements will be mutually agreed by Netscape and Concentric.

11.  REPORTING, AUDIT RIGHTS AND MILESTONES.

     11.1 Reporting.  Within fifteen (15) days after the end of each month
          ---------                                                       
during the Term:  (i)  Concentric shall provide Netscape with a report in common
log format describing the total number of hits and page impressions for each of
the pages in the Service, and such other tracking information as the parties
shall mutually agree ("Access Logs"), and (ii) Netscape shall provide Concentric
                       -----------                                              
with a report describing the number of redirects of traffic to the Service from
Netscape's Web Site and such other tracking information as the parties shall
mutually agree.

     11.2.  Audit Rights.
            ------------ 

          (a) Concentric shall retain complete, clear and accurate records
regarding its activities under this Agreement.  Each June and December during
the Term, the parties shall review the financial results for the Service and
Access Logs.

          (b) Netscape shall retain complete, clear and accurate records
regarding its obligation to make Advertising Net Revenue Payments to Concentric
pursuant to Exhibit C.
            --------- 

          (c) Each party shall have the right, upon no less than fifteen (15)
days prior written notice to the other party, to cause an independent Certified
Public Accountant to inspect and audit, during the audited party's normal
business hours, all relevant records of the audited party upon which its
Payments under Exhibit C are based.  The costs of such audit shall be paid by
               ---------                                                     
the auditing party provided, however, that if said inspection shall reveal an
error in excess of five percent (5%) in monies due to the auditing party by the
audited party, the audited party shall pay for the audit.  Each party's audit
rights as described herein shall continue for two (2) months after the
expiration or termination of this Agreement.

     11.3.  Milestones.
            ---------- 

          (a) Netscape and Concentric agree to establish quarterly reviews of
the Service with the intent to review the success of the Service and agree to
modifications and improvements to the Service.

          (b) Netscape and Concentric agree to review the business plan for the
Service after twelve (12) months of its operation for the purpose of mutually
agreeing to revised Customer, gross revenue targets, net revenue targets, and
any other targets mutually agreed to by the parties (collectively "Milestones").
                                                                  ----------- 
The current targets are to reach monthly run rates of [*] per
month, [*] in gross revenues per month, and [*] in net revenues per month, by
the [*] month of the Service's operation. If the parties cannot mutually
agree to

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

                                       11
<PAGE>
 
revised Milestones, then the monthly run-rate Milestones for the next review
shall be set at double the average actual monthly gross revenues for months 9-
12, and net revenues shall be at [*] of such monthly gross revenues.

          (c) Netscape and Concentric agree to review the revised Milestones
three (3) months prior to the end of the Term (including any extension of the
Term) ("End-of-Term Review") for the purpose of:  (i) discussing the performance
        ------------------                                                      
of the Service and the desirability of extending the Term; and (ii)  mutually
agreeing to revised Milestones.

12.  TERM AND TERMINATION.

     12.1.  Term.  Unless earlier terminated pursuant to the provisions of
            ----                                                          
Section 12.2, the this Agreement shall remain in force for the Term. The Term
will automatically be extended for not more than [*] have been met. If such
Milestones [*] of the Term (including any extension of the Term), either party
may decline to extend the term by giving the other party written notice thereof
within three (3) business days following the applicable End-of-Term Review.

     12.2.  Termination for Cause.  Either party shall have the right to
            ---------------------                                       
terminate this Agreement upon a material default by the other party of any of
its material obligations under this Agreement, unless within thirty (30)
calendar days after written notice of such default the defaulting party remedies
such default.

     12.3.  Rights Upon Termination or Expiration.
            ------------------------------------- 

            (a)  Upon expiration or termination of this Agreement, at Netscape's
option, either:  (i)  Concentric shall remain obligated to provide support
service and maintenance operations for the Service for a period of six (6)
months from the time of termination or expiration on the terms and conditions of
this Agreement; and (ii) Netscape will (subject to Concentric's proprietary
rights) have the right to develop [*] and Concentric [*] to produce the Service.
In either event, upon the termination of its obligations to Netscape in regard
to the Service, Concentric will (subject to Netscape's proprietary rights) have
the right to produce a similar service, but Concentric will no longer have the
right to use the Service Name or the Service's domain name.

            (b)  Following the expiration or termination of this Agreement,
Netscape and Concentric will provide a transition period of six (6) months to
Customers, during which time Concentric and Netscape [*] provided by either
party. Netscape and Concentric [*] to Customers about such expiration or
termination if such communications take place through the operating channels of
the Service, provided that such agreement will not be unreasonably withheld or
delayed. If after such agreement, [*] After the period of [*] the Customer
accounts [*] the similar service they prefer will [*] In this case, equitably
shall be defined as near equal in terms of: (i) [*] (ii) [*] and (iii) [*] with
the Service.

            (c)  Following any termination or expiration of this Agreement,
Netscape shall have the right, without any additional payment, charge or royalty
to Concentric, to produce versions of the Service which do not include
Concentric's proprietary technology, logo or name but which might employ a
graphic user interface which is substantially similar to the graphic user
interfaces of the Service.

            (d)  In addition to the right to receive amounts payable at the 
time of the termination of expiration of this Agreement, Sections 8.4 ("Design
Reviews and Ownership"), 11.2 ("Audit Rights"), 12.3 ("Rights Upon Termination
or Expiration"), 12.4 ("No Compensation"), 13

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       12
<PAGE>
 
("Warranties and Indemnification"), 14 ("Limitation of Liability") and 15
("General"), and provisions on Exhibits attached hereto that provide for their
survival, shall survive the termination or expiration of this Agreement for any
reason. Provisions of other Sections which, by their nature, must remain in
effect beyond the termination or expiration of this Agreement, shall also
survive termination or expiration of this Agreement for any reason.

     12.4.  No Compensation.  Neither party shall be entitled to any
            ---------------                                         
compensation, damages or payments in respect to goodwill that has been
established or for any damages on account of prospective profits or anticipated
sales, and shall not be entitled to reimbursement in any amount for any
training, advertising, market development, investments, leases or other costs
that shall have been expended by it before the expiration or termination of this
Agreement, regardless of the reason for or method of termination of this
Agreement.  Each party hereby waives its rights under applicable laws for any
such compensation, reimbursement or damages.

13.  WARRANTIES AND INDEMNIFICATION

     13.1   Title.
            ----- 

            (a)  Concentric warrants that (i)  it has the right to perform the
services set forth in this Agreement, (ii) such performance does not infringe on
any third parties' proprietary or personal rights, (iii) it owns or licenses all
rights, title and interest in and to the technology underlying the production of
the Service, (iv) Netscape shall not be obligated to pay any fees or royalties
in connection with the Service other than as specifically set forth in this
Agreement, and (v) there are no pending or threatened lawsuits concerning any
aspect of the Service or the technology underlying the Service.

            (b)  Netscape warrants that (i)  it has the right to perform the
services set forth in this Agreement, (ii) such performance does not infringe on
any third parties' proprietary or personal rights, (iii) it owns or licenses all
rights, title and interest in and to Netscape Design Contributions, (iv)
Concentric shall not be obligated to pay any fees or royalties in connection
with the Service other than as specifically set forth in this Agreement, and (v)
to the best of Netscape's knowledge, there are no pending or threatened lawsuits
concerning any aspect of the Service or the technology underlying the Service.

     13.2.  Performance.  Concentric warrants that the Service will function
            -----------                                                     
substantially in accordance with the specifications set forth in this Agreement
and as the parties may determine from time to time.  Concentric shall repair any
malfunctions of the Service within a reasonable period of time (not to exceed
two (2) days) after notice by any party of such condition.

     13.3   Responsibility.  Concentric represents and warrants to Netscape that
            --------------                                                      
the [*] (other than the [*] which will appear on the Service or any other areas
related to the Service, and [*] will not violate any criminal laws or any rights
of any third parties, including, but not limited to, infringement or
misappropriation of any copyright, patent, trademark, trade secret, music,
image, or other proprietary or property right, false advertising, unfair
competition, defamation, invasion of privacy or rights of celebrity, violation
of any antidiscrimination law or regulation, or any other right of any person or
entity, or otherwise violate any applicable local, state, national or
international law.

     13.4.  Disclaimer.  THE WARRANTIES PROVIDED BY CONCENTRIC HEREIN ARE THE
            ----------                                                       
ONLY WARRANTIES PROVIDED BY EITHER PARTY WITH RESPECT TO THE SERVICES.  EACH
PARTY DISCLAIMS ANY AND ALL OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING ANY
IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, WITH
RESPECT TO THE SERVICES.


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

                                       13
<PAGE>
 
     13.5.  Indemnification.
            --------------- 

            (a)  Concentric agrees to indemnify Netscape and to hold Netscape
harmless from any and all liability, loss, damages, claims, or causes of action,
including reasonable legal fees and expenses that may be incurred by Netscape,
arising out of or related to Concentric's breach of any of the foregoing
representations and warranties or arising from third party claims alleging that
[*] of the Service granted by Concentric hereunder infringes any trademark,
copyright, or trade secret of any third party. In connection with such
indemnification, Netscape will (i) promptly notify Concentric in writing of any
such claim and grant Concentric control of the defense and all related
settlement negotiations, and (ii) cooperate with Concentric, at Concentric's
expense, in defending or settling such claim; provided that if any settlement
results in any ongoing liability to, or prejudices or detrimentally impacts
Netscape, and such obligation, liability, prejudice or impact can reasonably be
expected to be material, then such settlement shall require Netscape's written
consent. In connection with any such claim, Netscape may have its own counsel in
attendance at all public interactions and substantive negotiations at its own
cost and expense.

            (b)  Netscape agrees to indemnify Concentric and to hold Concentric
harmless from any and all liability, loss, damages, claims, or causes of action,
including reasonable legal fees and expenses that may be incurred by Concentric,
arising out of or related to Netscape's breach of any of the foregoing
representations and warranties or arising from third party claims alleging that
[*] of the Service granted by Netscape hereunder infringes any copyright or
trade secret of any third party. In connection with such indemnification,
Concentric will (i) promptly notify Netscape in writing of any such claim and
grant Netscape control of the defense and all related settlement negotiations,
and (ii) cooperate with Netscape, at Netscape's expense, in defending or
settling such claim; provided that if any settlement results in any ongoing
liability to, or prejudices or detrimentally impacts Concentric, and such
obligation, liability, prejudice or impact can reasonably be expected to be
material, then such settlement shall require Concentric's written consent. In
connection with any such claim, Concentric may have its own counsel in
attendance at all public interactions and substantive negotiations at its own
cost and expense.

14.  LIMITATION OF LIABILITY.  [*] IN NO EVENT WILL EITHER PARTY BE LIABLE FOR
ANY LOST PROFITS OR ANY FORM OF INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL
DAMAGES OF ANY CHARACTER FROM ANY CAUSES OF ACTION OF ANY KIND WITH RESPECT TO
THIS AGREEMENT OR THE TECHNOLOGY LICENSED HEREUNDER, WHETHER ARISING IN TORT
(INCLUDING NEGLIGENCE), CONTRACT, OR OTHERWISE, EVEN IF IT HAS BEEN INFORMED IN
ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES.

15.  GENERAL.

     15.1.  Governing Law.  This Agreement shall be subject to and governed in 
            ------------- 
all respects by the statutes and laws of the State of California without regard
to the conflicts of laws principles thereof. The Superior Court of Santa Clara
County and/or the United States District Court for the Northern District of
California shall have exclusive jurisdiction and venue over all controversies in
connection herewith, and each party hereby consents to such exclusive and
personal jurisdiction and venue.

     15.2.  Entire Agreement.  This Agreement, including the exhibits and 
            ---------------- 
attachments referenced on the signature page hereto, constitutes the entire
Agreement and understanding between the parties and integrates all prior
discussions between them related to its subject matter. No modification of any
of the terms of this Agreement shall be valid unless in writing and signed by an
authorized representative of each party.


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

                                       14
<PAGE>
 
     15.3.  Assignment.
            ----------

            (a)  Concentric may not assign any of its rights or delegate any of
its duties under this Agreement, or otherwise transfer this Agreement (by
merger, operation of law or otherwise) without the prior written consent of
Netscape. Any attempted assignment, delegation or transfer in derogation hereof
shall be null and void.

            (b)  In the event of any Change of Control of Concentric, Netscape
will have the right to terminate this Agreement upon thirty (30) days prior
written notice to Concentric. "CHANGE OF CONTROL" means any transaction(s) as a
result of which either: (i) more than 20% of Concentric's voting securities are
held by a single individual or legal entity; or (ii) [*] For the purposes of 
Subsection (ii) [*]

            (c)  Notwithstanding Section 15.3(a) and 15.3(b) above, Concentric
shall have the right to reincorporate under the laws of any State without the
prior consent of Netscape.

     15.4.  Notices.  All notices required or permitted hereunder shall be 
            -------
given in writing addressed to the respective parties as set forth below and
shall either be (i) personally delivered, (ii) transmitted by postage prepaid
certified mail, return receipt requested, or (iii) transmitted by nationally-
recognized private express courier, and shall be deemed to have been given on
the date of receipt if delivered personally, or two (2) days after deposit in
mail or express courier. Either party may change its address for purposes hereof
by written notice to the other in accordance with the provisions of this
Subsection. The addresses for the parties are as follows:

     CONCENTRIC:                         NETSCAPE:
 
     Concentric Network Corporation      Netscape Communications Corporation
     10590 N. Tantau Avenue              501 East Middlefield Road, MV-002 
     Cupertino, CA  95014                Mountain View, CA 94043               
     Fax: (408) 342-2876                 Fax: (415) 528-4123                   
     Attn: Mike Anthofer,                Attn: General Counsel                  
     Senior Vice President               
      and Chief Financial Officer
 

     15.5.  Confidentiality.  Subject to the terms and conditions of the 
            ---------------
Non-Disclosure Agreement attached hereto as Exhibit F, all disclosures of
proprietary and/or confidential information in connection with this Agreement as
well as the contents of this Agreement, the financial arrangements described in
this Agreement, the Third Party Providers, advertising sales, [*] and [*]
related to the Service shall be governed by the terms of the Mutual Non-
Disclosure Agreement attached hereto as Exhibit H. The information contained in
                                        ---------
the reports provided by each party hereunder shall be deemed the Confidential
Information of the disclosing party. Notwithstanding the foregoing, Netscape
may, in its sole discretion, make publicly available the auditing of traffic
results and indicate that [*] of the information.

     15.6.  Force Majeure.  Neither party will be responsible for any failure 
            -------------
to perform its obligations under this Agreement due to causes beyond its
reasonable control, including but not limited to, acts of God, war, riot,
embargoes, acts of civil or military authorities, fire, floods or accidents,
provided that (a) such party promptly notifies the other party thereof and (b)
such failure does not continue for more than three (3) days.

     15.7.  Waiver.  The waiver, express or implied, by either party of any 
            ------
breach of this Agreement by the other party will not waive any subsequent breach
by such party of the same or a different kind.


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

                                       15
<PAGE>
 
     15.8.  Headings.  The headings to the Sections and Subsections of this 
            --------
Agreement are included merely for convenience of reference and shall not affect
the meaning of the language included therein.

     15.9.  Independent Contractors.  The parties acknowledge and agree that 
            -----------------------
they are dealing with each other hereunder as independent contractors. Nothing
contained in this Agreement shall be interpreted as constituting either party
the joint venturer, employee or partner of the other party or as conferring upon
either party the power of authority to bind the other party in any transaction
with third parties.

     15.10. Severability. In the event any provision of this Agreement is held 
            ------------
by a court or other tribunal of competent jurisdiction to be unenforceable, such
provision shall be reformed only to the extent necessary to make it enforceable,
and the other provisions of this Agreement will remain in full force and effect.

     15.11. Counterparts.  This Agreement may be executed in two or more 
            ------------
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument. For purposes hereof, a
facsimile copy of this Agreement, including the signature pages hereto, shall be
deemed to be an original. Notwithstanding the foregoing, the parties shall
deliver original execution copies of this Agreement to one another as soon as
practicable following execution thereof.

 
The parties have duly executed this Agreement as of the later of the two (2)
 dates set forth below.

CONCENTRIC:                                NETSCAPE:                          
                                                                              
CONCENTRIC NETWORK                         NETSCAPE COMMUNICATIONS            
 CORPORATION                               CORPORATION                        
                                                                              
                                                                              
By: /s/                                    By: /s/
   ---------------------------------          --------------------------------  
Print Name:                                Print Name:                        
           -------------------------                  ------------------------  
Title:                                     Title:                             
      ------------------------------             -----------------------------  
Date:                                      Date:                              
     ------------------------------             ------------------------------

Concentric Network                         Netscape Address:                  
 Corporation                                                                  
10590 N. Tantau Avenue                     501 East Middlefield Road, MV-002  
Cupertino, CA  95014                       Mountain View, California  94043   
USA                                        USA                                
Attention:  Mike Anthofer                  Attention:  General Counsel        
Facsimile:  (408) 342-2876                 Facsimile:  (415) 528-4123         
Email:                                     Email:                              
      -----------------------------              -----------------------------  
Effective Date: June 23, 1997

                                       16
<PAGE>
 
                                   EXHIBIT A
                             ADDITIONAL DEFINITIONS

"Concentric Brand Service" means the Concentric service which currently
 ------------------------                                              
includes: establishing a presence on the Internet, site traffic monitor,
managing multiple email accounts, file storage and the posting of HTML pages to
the Internet.  "ConcentricHost" currently consists of the following three
services:  (i) ConcentricHost HomeOffice", (ii) "ConcentricHost SmallBusiness",
and (iii) "ConcentricHost Premium".


"CONCENTRIC WEB SITE" consists of Web pages managed and hosted by Concentric,
 -------------------                                                         
including but not limited to the following Universal Resource Locators (URLs):

http://www.concentric.net
http://enterprise.concentric.net
http://home.concentric.net.

Target Market:  [*]
- -------------                                                               


Term:     [*]
- ----                                       


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

                                       17
<PAGE>
 
                                   EXHIBIT B
                              NETSCAPE'S WEB SITE



URL:  http://home.netscape.com
- ---                           

                                       18
<PAGE>
 
                                   EXHIBIT C
                                   ---------
                           REVENUE SPLITS AND BILLING


                                     [*]

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions. A total of 2 pages has been 
omitted from this Exhibit.


                                       19
<PAGE>
 
                                     [*]

 
[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions. A total of 2 pages has been 
omitted from this Exhibit.
 


                                       20
<PAGE>
 
                                   EXHIBIT D
                               ROLL-OUT SCHEDULE


[*]

 
[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

<PAGE>
 
                                   EXHIBIT E
                             CUSTOMER REGISTRATION


1.   Registration Process.
     -------------------- 

     (a) Initially, the Service will use the [*] in conjunction with a 
[*] presented to new Customers.  At the time the Customer is asked
to register, the Customer will be notified as to what data is required for them
to provide, how the data will be used and who will have access to the data.
Concentric will [*] at a time interval and format to be mutually agreed upon 
by the parties.

     (b) The parties hereto acknowledge that it is their intent to integrate the
Service' user registration processes with Netscape's "Universal Registration"
system when such system becomes available. At such time as each registration
process is transferred to Netscape, Netscape shall use reasonable commercial
efforts [*] process as [*] by Concentric. At such time as Netscape's "Universal
Registration" system is deployed, Netscape will provide to [*] in a format and
timeframe to be mutually agreed upon by Netscape and Concentric. Netscape and
Concentric shall use reasonable commercial efforts to coordinate the [*] from
Netscape to Concentric at such time as Netscape's "Universal Registration"
system is used in connection with the Service.

2.   Additional User Information.  If Concentric collects information about
     ---------------------------                                           
users accessing the Service, in addition to information supplied during the
registration process, such information shall be made available to Netscape in a
format and timeframe as the parties shall mutually agree.

3.   Personal Data Confidential;  Ownership.  Except as mutually agreed by
     --------------------------------------                               
Netscape and Concentric, [*] as well as [*] shall be the [*] of, and [*]
Netscape and Concentric, provided that:

     (a)  names shall not be resold or disclosed to third parties;

     (b)  [*]

     (c)  [*]

     (d)  [*]

     (e)  Netscape and Concentric must agree to user disclosure requirements
          that are consistent with the Open Profiling Standard (OPS).

Both Netscape and Concentric will have rights to [*] If either party [*] while
in the Service, both Concentric and Netscape will have rights to the additional
information. In the event of an acquisition or merger of Concentric with a [*]
Netscape, Concentric will forfeit its [*] acquired through the Service. Such
named companies are [*]



[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       22
<PAGE>
 
                                   EXHIBIT F
                        MUTUAL NON-DISCLOSURE AGREEMENT

This mutual Confidential Disclosure Agreement ("Agreement") is entered into
between Netscape Communications Corporation ("Netscape") and Concentric Network
Corporation ("Company"), and is effective as of the date of execution by
Netscape ("Effective Date").  Each party (the "Receiving Party") understands
that the other party (the "Disclosing Party") may disclose certain Confidential
Information (as defined in Section 1 below) under this Agreement.  Netscape and
Company agree as follows:

1.   DEFINITION.  "Confidential Information" shall mean (i) all information
     disclosed in tangible form by the Disclosing Party and marked
     "confidential" or "proprietary", and (ii) all information disclosed orally
     or otherwise in intangible form by the Disclosing Party and designated as
     confidential or proprietary at the time of disclosure.  Confidential
     Information may include, without limitation, computer programs, code,
     algorithms, names and expertise of employees and consultants, know-how,
     formulas, processes, ideas, inventions (whether patentable or not),
     schematics and other technical, business, financial and product development
     plans, forecasts, strategies and information.

2.   PURPOSE.  The Receiving Party shall use the Confidential Information only
     for the following purpose:  to fulfill each party's commitments under the
     Co-Marketing Services Agreement dated June 23, 1997.

3.   CONFIDENTIALITY OBLIGATION.  The Receiving Party agrees to protect the
     Confidential Information by using the same degree of care, but not less
     than a reasonable degree of care, to prevent the unauthorized use,
     dissemination or publication of the Confidential Information as the
     Receiving Party uses to protect its own confidential or proprietary
     Information of a like nature.  The Receiving Party shall limit the use of
     and access to the Disclosing Party's Confidential Information to the
     Receiving Party's employees or independent contractors who need to know
     such Confidential Information for the purpose set forth in Section 2 above
     and who have entered into binding obligations of confidentiality
     substantially similar to the obligations set forth herein.

4.   TERM.  The Receiving Party's obligations to protect Confidential
     Information hereunder shall expire 3 years from the date of each such
     disclosure of Confidential Information, except when such Confidential
     Information disclosed by the Disclosing Party is source code, in which case
     the Receiving Party's obligations to protect such Confidential Information
     shall be perpetual.

5.   EXCLUSIONS.  Confidential Information as defined in Section 1 above shall
     not include Confidential Information that:  (i) is or becomes a matter of
     public knowledge through no fault of the Receiving Party; or (ii) was in
     the Receiving Party's possession or known by it prior to receipt from the
     Disclosing Party; or (iii) was rightfully disclosed to the Receiving Party
     by another person without restriction; or (iv) is independently developed
     by the Receiving Party without access to such Confidential Information.
     The Receiving Party may disclose Confidential Information pursuant to any
     statutory or regulatory authority or court order, provided the Disclosing
     Party  is given prompt written notice of such requirement and the scope of
     such disclosure is limited to the extent possible.

6.   RETURN OF CONFIDENTIAL INFORMATION.  Upon written request by the Disclosing
     Party at any time, the Receiving Party shall:  (i) turn over to the
     Disclosing Party all Confidential Information of the Disclosing Party, all
     documents or media containing the Confidential Information, and any and all
     copies or extracts thereof, or (ii) destroy the Confidential Information,
     and any and all copies or extracts thereof, and provide the Disclosing
     Party with written certification of such destruction signed by an
     authorized representative of the Receiving Party.

                                       23
<PAGE>
 
7.   EQUITABLE RELIEF.  The Receiving Party acknowledges and agrees that due to
     the unique nature of the Disclosing Party's Confidential Information, there
     may be no adequate remedy at law for any breach of its obligations.  The
     Receiving Party further acknowledges that any such breach may allow the
     Receiving Party or third parties to unfairly compete with the Disclosing
     Party resulting in irreparable harm to the Disclosing Party, and,
     therefore, that upon any such breach or any threat thereof, the Disclosing
     Party shall be entitled to seek appropriate equitable relief in addition to
     whatever remedies it may have at law.  The Receiving Party will notify the
     Disclosing Party in writing immediately upon the occurrence of any such
     unauthorized release or other breach.

8.   INTELLECTUAL PROPERTY RIGHTS.  Neither party acquires any intellectual
     property rights under this Agreement or through any disclosure hereunder,
     except the limited right to use such Confidential Information in accordance
     with this Agreement.

9.   WARRANTY.  The Confidential Information disclosed under this Agreement is
     delivered "AS IS", and all representations or warranties, whether express
     or implied, including warranties or conditions for fitness for a particular
     purpose, merchantability, title and noninfringement are hereby disclaimed.

10.  NETSCAPE SUBSIDIARIES.  Netscape's wholly owned subsidiaries, by signing
     this Agreement on behalf of Netscape and returning a fully executed
     original or copy to the Netscape Legal Department, shall be entitled to
     disclose Netscape's Confidential Information and receive Company's
     Confidential Information on behalf of Netscape under this Agreement,
     provided such subsidiaries comply with the terms and conditions of this
     Agreement and further provided such disclosures or receipt of Confidential
     Information are governed by the terms and conditions of this Agreement.

11.  GENERAL.  This Agreement supersedes all prior discussions and writings with
     respect to the subject matter hereof, and constitutes the entire agreement
     between the parties with respect to the subject matter hereof.  No waiver
     or modification of this Agreement will be binding upon either party unless
     made in writing and signed by a duly authorized representative of each
     party and no failure or delay in enforcing any right will be deemed a
     waiver.  The parties understand that nothing herein requires either party
     to proceed with any proposed transaction or relationship in connection with
     which Confidential Information may be disclosed.  In the event that any of
     the provisions of this Agreement shall be held by a court or other tribunal
     of competent jurisdiction to be unenforceable, the remaining portions
     hereof shall remain in full force and effect.  This Agreement shall be
     governed by the laws of the State of California without regard to conflicts
     of laws provisions thereof and each party submits to the jurisdiction and
     venue of California State or federal court generally serving the Santa
     Clara county area with respect to the subject matter of this Agreement.
     The headings to the Sections of this Agreement are included merely for
     reference and shall not affect the meaning of the language included
     therein.  This Agreement is written in the English language only, which
     language shall be controlling in all respects.  Les parties aux presentes
     confirment leur volonte que cette convention de meme que tous les documents
     y compris tout avis qui s'y rattache, soient rediges en langue anglaise
     (translation:  "The parties confirm that this Agreement and all related
     documentation is and will be in the English language.")

                                       24
<PAGE>
 
COMPANY:                                 NETSCAPE:                           
                                                                             
CONCENTRIC NETWORK CORPORATION           NETSCAPE COMMUNICATIONS CORPORATION 
                                                                             
By: /s/                                  By: /s/                                
   ---------------------------               ---------------------------   
Print Name:                              Print Name:                         
           -------------------                      --------------------   
Title:                                   Title:                              
      ------------------------                 -------------------------   
Date:                                    Date:                               
     -------------------------                --------------------------   
                                                                             
Company Address:                         Netscape Address:                   
10590 N. Tantau Avenue                   501 East Middlefield Road, MV-002   
Cupertino, California  95014             Mountain View, California  94043    
USA                                      USA                                  

                                       25

<PAGE>
 
                                                                   EXHIBIT 10.39


                          TRADEMARK LICENSE AGREEMENT

This Trademark License Agreement ("AGREEMENT") is effective as of the 23rd day
of June, 1997 ("EFFECTIVE DATE") and is entered into by and between Netscape
Communications Corporation ("NETSCAPE"), a Delaware corporation located at 501
East Middlefield Road, Mountain View California 94043, and Concentric Network
Corporation ("CONCENTRIC"), a Florida corporation located at 10590 N. Tantau
Avenue, Cupertino, California 95014.

                                    RECITALS

A.   Netscape owns and uses the names and/or trademarks NETSCAPE and NETSCAPE
     VIRTUAL OFFICE and any applications or registrations therefor as listed on
                                                                               
     Exhibit A attached hereto (collectively referred to as the "MARKS"), in
     ---------                                                              
     connection with its Internet-related software products, services and
     technology;

B.   Concentric is in the business of offering certain Internet and Intranet-
     related services;

C.   Concentric desires to use the trademarks NETSCAPE and NETSCAPE VIRTUAL
     OFFICE solely in the titles set forth in Exhibit B in connection with
                                              ---------                   
     Intranet Service in the languages and geographic territories set forth
     opposite such titles in Exhibit B; and
                             ---------     

D.   Netscape is willing to permit such use of the Marks under the terms and
     conditions set forth in this Agreement.

NOW THEREFORE, THE PARTIES AGREE AS FOLLOWS:

1.   GRANT OF LICENSE.

     1.1  GRANT OF LICENSE.  Netscape hereby grants to Concentric a non-
exclusive, non-transferable, license to use the Marks in the title set forth in
                                                                               
Exhibit B solely in conjunction with [*] 
- ---------                                                                 
opposite such title (the "INTRANET SERVICE") which Intranet Service: (a) shall
promote Netscape's products and services; (b) shall be jointly developed by
Netscape and Concentric; and (c) shall reside [*] at a location to be mutually
agreed upon by both parties deploying Concentric's servers and be located [*]
from Netscape's web site. Concentric may only use the Marks as a part of the
complete title specified in Exhibit B and shall not separately use any element
                            ---------
or elements of the Marks.

     1.2  RESERVATION OF RIGHTS.  Netscape hereby reserves any and all rights
not expressly and explicitly granted in this Agreement, including Netscape's
right to authorize or license use of the Marks or any other trademarks or names
containing NETSCAPE, to any third party for use in connection with any goods and
services, including, but not limited to, Intranet Service.  Without limiting the
rights reserved in the preceding sentence, Netscape hereby reserves any and all
rights to use, authorize use or license use of the Marks or any other trademarks
or names containing NETSCAPE in any geographic territory listed in Exhibit B in
                                                                   ---------   
a language or language(s), or in any other territory in any language, different
from the language listed next to such geographic territory in Exhibit B.  No
                                                              ---------     
right is provided to use any other Netscape trademark, including without
limitation the Netscape Horizon Logo.


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.

<PAGE>
 
2.   LICENSE FEE.  For the rights granted to Concentric herein, Concentric shall
pay Netscape license fee of Five million dollars ($5,000,000) payable as
follows:

     (a) Two million dollars ($2,000,000) payable by June 30, 1997; and

     (b) Three million dollars ($3,000,000) payable by July 30, 1997.

The license fee due hereunder is exclusive of any applicable taxes.  Concentric
shall be responsible for all applicable national, state and local taxes, value
added or sales taxes, exchange, interest, banking, collection and other charges
and levies and assessments pertaining to payments other than U.S. taxes based on
Netscape's net income.  If Concentric is required by law to make any deduction
or to withhold from any sum payable to Netscape by Concentric hereunder, (i)
Concentric shall effect such deduction or withholding, remit such amounts to the
appropriate taxing authorities and promptly furnish Netscape with tax receipts
evidencing the payments of such amounts, and (ii) the sum payable by Concentric
upon which the deduction or withholding is based shall be increased to the
extent necessary to ensure that, after such deduction or withholding, Netscape
receives and retains, free from liability for such deduction or withholding, a
net amount equal to the amount Netscape would have received and retained in the
absence of such required deduction or withholding.

3.   OWNERSHIP OF MARKS.  Concentric hereby acknowledges that Netscape is the
owner of the Marks, and any trademark applications and/or registrations thereto,
agrees that it will do nothing inconsistent with such ownership and agrees that
all use of the Marks by Concentric shall solely inure to the benefit of
Netscape.  Concentric agrees that nothing in this Agreement shall give
Concentric any right, title or interest in the Marks other than the right to use
the Marks in accordance with this Agreement.  Concentric agrees not to register
or attempt to register the Marks as a trademark, service mark, Internet domain
name, trade name, or any similar trademarks or name, with any domestic or
foreign governmental or quasi-governmental authority or otherwise.  Concentric
may not register or use the Marks or an abbreviation of the Marks as part of an
Internet domain name.  The provisions of this paragraph shall survive the
expiration or termination of this Agreement.

4.   USE OF THE MARKS; PROTECTION OF THE MARKS.

     4.1  PROPER USE.  Concentric agrees that all use of the Marks shall only
occur in connection with the Intranet Service and shall be in strict compliance
with the terms of this Agreement.  Concentric may use the Marks as set forth in
Section 1.1 as well as in connection with the promotion of the Intranet Service,
excluding merchandising or any software products.  Use of the Marks for
promotional purposes shall be submitted to Netscape for approval at least twenty
(20) business days prior to the promotional use of the Mark.  The Marks shall
always be used in the English language; however the VIRTUAL OFFICE term portion
of the Mark may be translated, upon approval by Netscape, to the non-English
designated language(s) listed in Exhibit B, if any.  No other modifications to
                                 ---------                                    
the Marks shall be made.  Concentric shall use the Marks in conformance with
Netscape's trademark guidelines ("TRADEMARK GUIDELINES"), set forth in Exhibit
                                                                       -------
C, which Trademark Guidelines may be revised by Netscape from time to time.
- -
Concentric agrees not to use any other trademark or service mark in combination
with the Marks other than as described in Section 1.1.  Concentric has no right
to sublicense, transfer, translate (except as provided in this Section 4.1) or
assign the use of the Marks or use the Marks for any other purpose other than
the purpose described herein.  Concentric may not use the Mark in connection
with, or for the benefit of, any third party's products or services.  Concentric
further agrees not to use the Marks on or in connection with any products or
services that are or could be deemed by Netscape, in its reasonable judgment, to
be obscene, pornographic, disparaging of Netscape or its products or products,
or otherwise in poor taste, or that are themselves unlawful or whose purpose is
to encourage unlawful activities by others.

                                       2
<PAGE>
 
     4.2  QUALITY STANDARDS.  Concentric agrees to maintain a consistent level
of quality of the Intranet Service performed in connection with the Marks
substantially equal to that found in Concentric's existing services.  Concentric
further agrees to maintain a level of quality in connection with its use of the
Marks that is consistent with general industry standards.

     4.3  MONITORING BY NETSCAPE.  Concentric acknowledges that Netscape has no
further obligations under this Agreement other than the right to periodically
monitor Concentric's use of the Marks in conjunction with the Intranet Service.
Upon request by Netscape, Concentric shall provide Netscape with representative
samples of each such use prior to the time the Marks are utilized on the
Internet, on an Intranet or in press materials or marketing or advertising
materials.  If Netscape determines that Concentric is using the Marks
improperly, and/or in connection with Intranet Service which do not meet the
standards set forth in Section 4.1 or Section 4.2, Netscape shall notify
Concentric, and Concentric shall remedy the improper use within two (2) business
days following receipt of such notice from Netscape.  Use of the Marks on goods
or services other than the Intranet Service or the promotion of the Intranet
Service, or in a manner inconsistent with the Trademark Guidelines, shall
constitute material breach of this Agreement.  If such material breach has not
been cured within two (2) business days following receipt of notice from
Netscape, this Agreement shall be terminated.

     4.4  LEGEND; DISCLAIMER.  Concentric shall include with any online
publication or publication in print containing the Marks a trademark legend
indicating that "Netscape is a trademark of Netscape Communications Corporation
registered in the US and in other jurisdictions and that the Marks are used
under license",  and a disclaimer that Concentric and not Netscape has produced
the Intranet Service and is responsible for the content thereof.

     4.5  NAVIGATION SERVICES.  If Netscape reasonably determines that the
[*] contain or present any material that constitutes an infringement of
Netscape's trademark, patents, copyrights or trade secrets, Concentric's right
to use the Marks pursuant to the grant described in Section 1.1 shall, upon
written notice from Netscape of such determination, be suspended until
Concentric has revised, removed or removed links to such material to
Netscape's reasonable satisfaction. If such revision or removal of, or removal
of links to, such material to Netscape's reasonable satisfaction has not
occurred within thirty (30) days of the notice from Netscape described in the
preceding sentence, Netscape may immediately terminate the license grant
described in Section 1.1. If Netscape reasonably determines that the Internet
Services contains or presents any material that could reasonably constitute an
infringement of a third party's copyright, trademark, patents or trade
secrets, Netscape may immediately terminate this Agreement if Concentric has
not revised to Netscape's reasonable satisfaction that material or
presentation within one (1) business day of written notice from Netscape.

     4.6  CONCENTRIC WEB SITES.  If Netscape, in its sole discretion, at any
time determines that [*], or any services provided by Concentric, contain any
material or present any material in a manner that Netscape reasonably deems
inaccurate or an improper tarnishment of Netscape, the Netscape products or
the Marks, or an infringement of Netscape's or a third party's rights,
including but not limited rights under trademark, patent, trade secret or
copyright laws, or unlawful in any country or territory, Netscape may
immediately terminate this Agreement if Concentric has not revised to
Netscape's reasonable satisfaction that material or presentation within three
(3) business days of written notice from Netscape; provided, however, that
Netscape's rights and Concentric's obligations under this paragraph will not
apply to material or presentations that are not within Concentric's control.

5.   CONFIDENTIAL INFORMATION AND DISCLOSURE.  Unless required by law, and
except to assert its rights hereunder or for disclosures to its own employees on
a "need to know" basis, each party agrees not to disclose the terms of this
Agreement or matters relating thereto without the prior written consent of the
other party, which consent shall not be unreasonably withheld.

 
[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                      3
<PAGE>
 
6.   INDEMNIFICATION.

     6.1  INDEMNIFICATION BY CONCENTRIC.  Concentric agrees to indemnify
Netscape and to hold Netscape harmless from any and all liability, loss,
damages, claims or causes of action, including reasonable legal fees and
expenses that may be incurred by Netscape, arising out of performance of this
Agreement, the operation of the Intranet Service, or Concentric's use of the
Marks and content on Concentric's web sites or services linked to or presented
or offered in conjunction with the Marks, except for liability, loss, damages,
claims or causes of action arising out of third party claims (i) that
Concentric's use of the Marks infringe that third party's valid and subsisting
U.S. trademark registration in the Marks or (ii) in respect of any act or
omission of Netscape giving rise to liability.  Netscape shall provide
Concentric with prompt written notice of any claim for which indemnification is
sought and cooperating fully with and allowing Concentric to control the defense
and settlement of such claim.  Netscape may not settle any such claim without
Concentric's prior written consent, which consent shall not be unreasonably
withheld.  Netscape shall have the right, at its own expense, to participate in
the defense of any such claim.

     6.2  INDEMNIFICATION BY NETSCAPE.  Netscape agrees to indemnify Concentric
and to hold Concentric harmless from any and all liability, loss, damages,
claims or causes of action, including reasonable legal fees and expenses that
may be incurred by Concentric, arising out of a third party claim that [*]
Concentric shall provide Netscape with prompt written notice of any claim for
which indemnification is sought and cooperating fully with and allowing
Netscape to control the defense and settlement of such claim. Concentric may
not settle any such claim without Netscape's prior written consent, which
consent shall not be unreasonably withheld. Concentric shall have the right,
at its own expense, to participate in the defense of any such claim.

7.   TERMINATION

     7.1   TERM AND TERMINATION.  [*] in Section 4.3, Section 4.5 or this
Section 7.1. Netscape shall have the right to terminate this Agreement upon
the occurrence of one or more of the following: (a) any material breach by
Concentric of its obligations under this Agreement which remains uncured for
thirty (30) days or more following written notice of such breach from
Netscape, (b) use of the Marks by Concentric in a manner which is disparaging
of Netscape or its products and services and which remains uncured for two (2)
days following notice from Netscape, (c) Concentric decides not to launch the
Intranet Service, or (d) the Intranet Service are discontinued.

     7.2   EFFECT OF TERMINATION.  Upon termination of the Agreement, 
Concentric agrees it shall immediately cease any and all use of the Marks.

8.   GENERAL

     8.1   GOVERNING LAW.  This Agreement shall be subject to and governed in 
all respects by the statutes and laws of the State of California without regard
to the conflicts of laws principles thereof. The Superior Court of Santa Clara
County and/or the United States District Court for the Northern District of
California shall have exclusive jurisdiction and venue over all controversies in
connection herewith, and each party hereby consents to such exclusive and
personal jurisdiction and venue.

     8.2   ENTIRE AGREEMENT.  This Agreement, including Exhibit A, Exhibit B, 
                                                        ---------  ---------
and Exhibit C attached hereto, constitutes the entire Agreement and
    ---------
understanding between the parties and integrates all prior discussions between
them related to its subject matter. No modification of any of the terms of this
Agreement shall be valid unless in writing and signed by an authorized
representative of each party.

[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       4
<PAGE>
 
     8.3   ASSIGNMENT.  Concentric may not assign any of its rights or delegate 
any of its duties under this Agreement, or otherwise transfer this Agreement (by
merger, operation of law or otherwise) without the prior written consent of
Netscape. Any attempted assignment, delegation or transfer in derogation hereof
shall be null and void.

     8.4   NOTICES.  All notices required or permitted hereunder shall be given 
in writing addressed to the respective parties as set forth below and shall
either be (a) personally delivered or (b) transmitted by nationally-recognized
private express courier, and shall be deemed to have been given on the date of
receipt if delivered personally, or two (2) days after deposit with such express
courier. Either party may change its address for purposes hereof by written
notice to the other in accordance with the provisions of this Subsection. The
addresses for the parties are as follows:

   CONCENTRIC:                            NETSCAPE:
 
   Concentric Network Corporation         Netscape Communications Corporation
   10590 N. Tantau Avenue                 501 East Middlefield Road, MV-002    
   Cupertino, CA  95014                   Mountain View, CA 94043              
   Fax: (408) 342-2876                    Fax: (415) 528-4123                  
   Attn: Mike Anthofer                    Attn: General Counsel                 
   Senior Vice President and
   Chief Financial Officer

     8.5  FORCE MAJEURE.  Neither party will be responsible for any failure to
perform its obligations under this Agreement due to causes beyond its reasonable
control, including but not limited to acts of God, war, riot, embargoes, acts of
civil or military authorities, fire, floods or accidents, provided that (a) such
party promptly notifies the other party thereof and (b) such failure does not
continue for more than three (3) days.

     8.6  WAIVER.  Any waiver, either expressed or implied, by either party of
any default by the other in the observance and performance of any of the
conditions, covenants of duties set forth herein shall not constitute or be
construed as a waiver of any subsequent or other default.

     8.7  HEADINGS.  The headings to the Sections and Subsections of this
Agreement are included merely for convenience of reference and shall not affect
the meaning of the language included therein.

     8.8  INDEPENDENT CONTRACTORS.  The parties acknowledge and agree that they
are dealing with each other hereunder as independent contractors.  Nothing
contained in the Agreement shall be interpreted as constituting either party the
joint venture or partner of the other party or as conferring upon either party
the power of authority to bind the other party in any transaction with third
parties.

     8.9  SURVIVAL. The provisions of Section 1.2 (Reservation of Rights), 3
(Ownership of Marks), 4.4 (Legend; Disclaimer), 5 (Confidential Information and
Disclosure), 6 (Indemnification), 7.2 (Effect of Termination) and 8 (General)
will survive any termination of this Agreement.

     8.10 EQUITABLE RELIEF.  Concentric recognizes and acknowledges that a
breach by Concentric of this Agreement will cause Netscape irreparable damage
which cannot be readily remedied in monetary damages in an action at law, and
may, in addition thereto, constitute an infringement of the Marks.  In the event
of any default or breach by Concentric that could result in irreparable harm to
Netscape or cause some loss or dilution of Netscape's goodwill, reputation, or
rights in the Marks, Netscape shall be entitled to immediate injunctive relief
to prevent such irreparable harm, loss, or dilution in addition to any other
remedies available.

     8.11 SEVERABILITY.  Except as otherwise set forth in this Agreement, the
provisions of this Agreement are severable, and if any one or more such
provisions shall be determined to be invalid, illegal or unenforceable, in whole
or in part, the validity, legality and enforceability of any of the remaining
provisions or portions thereof shall not in any way be affected thereby and
shall nevertheless be binding between the parties hereto.  Any such invalid,
illegal or unenforceable provision or portion thereof shall 

                                       5
<PAGE>
 
be changed and interpreted so as to best accomplish the objectives of such
provision or portion thereof within the limits of applicable law.

     8.12 ATTORNEY'S FEES.  In the event of any action, suit, or proceeding
brought by either party to enforce the terms of this Agreement, the prevailing
party shall be entitled to receive its costs, expert witness fees, and
reasonable attorneys fees and expenses, including costs and fees on appeal.
 
IN WITNESS WHEREOF, the parties have executed this Agreement as of the


 
CONCENTRIC NETWORK CORPORATION           NETSCAPE COMMUNICATIONS CORPORATION

 
By: /s/Henry R. Nothhaft                 By: /s/ Mike Homer
   ---------------------------------         ---------------------------------- 
Name:  Henry R. Nothhaft                 Name:   Mike Homer
     -------------------------------           -------------------------------- 
Title: Pres & CEO                        Title: Senior Vice President Marketing
      ------------------------------            ------------------------------- 
Date: 6/23/97                            Date:  6/23/97
     -------------------------------            -------------------------------


Exhibit A:  Licensed Netscape Trademarks
- ---------
 
Exhibit B:  Titles; Target Language and Geographic Combinations
- ---------

Exhibit C:  Trademark Guidelines
- ---------

                                       6
<PAGE>
 
                                   EXHIBIT A
                          LICENSED NETSCAPE TRADEMARKS

NETSCAPE                 U.S. FEDERAL TRADEMARK REGISTRATION NO. 2,027,552

NETSCAPE VIRTUAL OFFICE
<PAGE>
 
                                   EXHIBIT B
              TITLES; TARGET LANGUAGE AND GEOGRAPHIC COMBINATIONS

<TABLE>
<CAPTION>
                 Title                   Target Language        Geographic Territory
- ---------------------------------------  ---------------  --------------------------------
<S>                                      <C>              <C> 
NETSCAPE VIRTUAL OFFICE BY CONCENTRIC     [*]              [*]
</TABLE>


[*] Certain information on this page has been omitted and filed separately 
with the Securities and Exchange Commission. Confidential treatment has been 
requested with respect to the omitted portions.


                                       2
<PAGE>
 
                                   EXHIBIT C

TRADEMARK USE GUIDELINES


Netscape's Trademark Guidelines are published at the following URL:

     http://home.netscape.com/misc/trademarks.html#trademarks

<PAGE>
 
                                                                   EXHIBIT 23.2
 
              CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS
   
  We consent to the reference to our firm under the caption "Experts" and
"Selected Financial Data" and to the use of our report dated March 14, 1997
(except for Note 1 "The Company" and Note 5, as to which the date is June 23,
1997, and Note 10, as to which the date is July 30, 1997), in Amendment No. 5
to the Registration Statement (Form S-1) and the related Prospectus of
Concentric Network Corporation for the registration of 4,140,000 shares of its
common stock.     
                                             
                                          /s/ Ernst & Young LLP     
 
San Jose, California
   
July 30, 1997     
       


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