<PAGE> 1
EXHIBIT 5.1
[ROPES & GRAY LETTERHEAD]
, 2000
Cabletron Systems, Inc.
35 Industrial Way
Rochester, New Hampshire 03867
Ladies and Gentlemen:
Re: Cabletron Systems, Inc.
This opinion is furnished to you in connection with a registration
statement on Form S-4 (the "Registration Statement") filed with the Securities
and Exchange Commission (the "Commission") under the Securities Act of 1933, as
amended, for the registration of an aggregate of 7,250,000 shares of Common
Stock, par value $0.01 per share (the "Common Shares"), and 50,000 shares of
Series C Convertible Preferred Stock, par value $1.00 per share the "Preferred
Shares" and together with the Common Shares, the "Shares"), of Cabletron
Systems, Inc., a Delaware corporation (the "Company"). Up to 4,000,000 Common
Shares (such shares, the "Common Merger Shares" and together with the Preferred
Shares, the "Merger Shares") and all of the Preferred Shares will be issued in
exchange for shares of common stock, par value $.00001 per share ("Indus River
Common Stock"), shares of Series A Convertible Preferred Stock, par value
$.00001 per share, shares of Series B Convertible Preferred Stock, par value
$.00001 per share, shares of Series C Convertible Preferred Stock, par value
$.00001 per share, and shares of Series D Convertible Preferred Stock, par value
$.00001 per share, and all shares of Indus River Common Stock issuable under
options and warrants to purchase Indus River Common Stock (other than certain
excluded options) of Indus River Networks, Inc. ("Indus River"), pursuant to an
Agreement and Plan of Merger dated as of August 18, 2000 (the "Merger
Agreement"), among the Company, Indus River and Acton Acquisition, Inc. ("Merger
Sub"), a Delaware corporation and a wholly-owned subsidiary of the Company. The
Merger Agreement provides for Merger Sub to merge with and into Indus River (the
"Merger") and for Indus River to survive the Merger as a wholly-owned
subsidiary of the Company. In addition, up to 3,250,000 Common Shares may be
issued by the Company upon the conversion of the Preferred Shares in accordance
with the provisions of the Certificate of Designation, Preferences and Rights of
the Series C Convertible Preferred Stock of Cabletron Systems, Inc. (the
"Certificate of Designation").
We have acted as counsel for the Company in connection with the issuance of
the Merger Shares pursuant to the Merger. For purposes of our opinion, we have
examined and relied upon such documents, records, certificates and other
instruments as we have deemed necessary.
<PAGE> 2
We express no opinion as to the applicability of compliance with or effect
of Federal law or the law of any jurisdiction other than the Commonwealth of
Massachusetts and the corporate laws of the State of Delaware.
Based on the foregoing, we are of the opinion that the Merger Shares being
issued by the Company pursuant to the Merger and the Common Shares to be issued
upon conversion of the Preferred Shares, have been duly authorized and, when
issued in accordance with the Merger Agreement or in accordance with the terms
of the Certificate of Designation, as applicable, will be fully paid and
nonassessable.
We hereby consent to the filing of this opinion as part of the Registration
Statement and to the use of our name therein and in the related Proxy
Statement/Prospectus under the caption "Legal Matters."
This opinion is to be used only in connection with the issuance of the
Shares while the Registration Statement is in effect.
Very truly yours,
Ropes & Gray
-2-
