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<TITLE>TYPE: NT 10-Q</TITLE>
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<font size=-1>TYPE: NT 10-Q</font>
<br><font size=-1>SEQUENCE: 1</font>
<br><font size=-1>DESCRIPTION: LATE FILING OF FORM 10-Q</font>
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<p><font size=-1>UNITED STATES</font>
<br><font size=-1>SECURITIES AND EXCHANGE COMMISSION</font>
<p><font size=-1>Washington, D.C. 20549</font>
<p><font size=-1>FORM 12b-25</font>
<p><font size=-1>SEC FILE NUMBER <b>1-10228</b></font>
<p><font size=-1>NOTIFICATION OF LATE FILING</font></center>
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<td VALIGN=TOP WIDTH="20%"><font size=-1>(Check One):</font></td>
<td VALIGN=TOP WIDTH="54%"><font size=-1>[ ] Form 10-K and Form 10-KSB</font>
<br><font size=-1>[ } Form 20-F [ ] Form 11-K</font>
<br><font size=-1>[<b>X</b>] Form 10-Q and Form 10-QSB</font>
<br><font size=-1>[ ] Form N-SAR</font></td>
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<p><font size=-1>For Period Ended: <b><u>November 30, 1999</u></b></font>
<p><font size=-1>[_] Transition Report on Form 10-K</font>
<br><font size=-1>[_] Transition Report on Form 20-F</font>
<br><font size=-1>[_] Transition Report on Form 11-K</font>
<br><font size=-1>[_] Transition Report on Form 10-Q</font>
<br><font size=-1>[_] Transition Report on Form N-SAR</font>
<p><font size=-1>For the Transition Period Ended:</font>
<br>
<br>
<p><font size=-1>Read Attached Instruction Sheet Before Preparing Form.
Please Print or Type.</font>
<p><font size=-1>NOTHING IN THIS FORM SHALL BE CONSTRUED TO IMPLY THAT
THE COMMISSION HAS VERIFIED ANY INFORMATION CONTAINED HEREIN.</font>
<br>
<br>
<p><font size=-1>If the notification relates to a portion of the filing
checked above, identify the Item(s) to which the notification relates:</font>
<p><u><font size=-1>Not applicable</font></u>
<p><font size=-1>PART I--REGISTRANT INFORMATION</font>
<p><u><font size=-1>Full Name of Registrant</font></u>
<br><b><font size=-1>Cabletron Systems, Inc.</font></b>
<p><u><font size=-1>Former Name if Applicable</font></u>
<br><font size=-1>Not applicable</font>
<p><u><font size=-1>Address of Principal Executive Office (Street and Number)</font></u>
<br><b><font size=-1>35 Industrial Way</font></b>
<p><u><font size=-1>City, State and Zip Code</font></u>
<br><b><font size=-1>Rochester, New Hampshire 03867</font></b>
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<br>
<br>
<br>
<p><font size=-1>PART II--RULES 12b-25(b) AND (c)</font>
<p><font size=-1>If the subject report could not be filed without unreasonable
effort or expense and the Registrant seeks relief pursuant to Rule 12b-25(b),
the following should be completed. (Check box if appropriate)</font>
<p><font size=-1>|(a) The reasons described in reasonable detail in Part
III of this form</font>
<br><font size=-1>| could not be eliminated without unreasonable effort
or expense;</font>
<p><font size=-1>|(b) The subject annual report, semi-annual report, transition
report</font>
<br><font size=-1>| on Form 10-K, Form 20-F, 11-K, or Form N-SAR, or portion
thereof,</font>
<br><font size=-1>[X]| will be filed on or before the fifteenth calendar
day following the</font>
<br><font size=-1>| prescribed due date; or the subject quarterly report
or transition</font>
<br><font size=-1>| report on Form 10-Q, or portion thereof, will be filed
on or before</font>
<br><font size=-1>| the fifth calendar day following the prescribed due
date; and</font>
<p><font size=-1>|(c) The accountant's statement or other exhibit required
by</font>
<br><font size=-1>Rule 12b-25(c) has been attached if applicable.</font>
<p><font size=-1>PART III--NARRATIVE</font>
<p><font size=-1>State below in reasonable detail the reasons why the Form
10-K and Form 10-KSB, 20-F, 11-K, 10-Q and Form 10-QSB, N-SAR, or the transition
report or portion thereof, could not be filed within the prescribed time
period. (ATTACH EXTRA SHEETS IF NEEDED )</font>
<p><font size=-1>As a result of Compaq Computer Corporation termination
of its OEM agreement with the Company, the Company is in the process of
resolving accounting issues related to this matter which effect the amount
of Other Income and Deferred Revenue in this quarter. The Company has been
unable to timely file its Quarterly Report on Form 10-Q without unreasonable
effort and expense. The Company anticipates filing its Quarterly Report
by the afternoon of Tuesday, January 18, 2000.</font>
<br>
<br>
<br>
<br>
<p><font size=-1>PART IV--OTHER INFORMATION</font>
<p><font size=-1>(1) Name and telephone number of person to contact in
regard to this notification</font>
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<center><u><font size=-1>David J. Kirkpatrick</font></u>
<br>(Name)</center>
</td>
<td VALIGN=TOP WIDTH="33%">
<center><u><font size=-1>(603)</font></u>
<br>(Area Code)</center>
</td>
<td VALIGN=TOP WIDTH="33%">
<center><u><font size=-1>332-9400</font></u>
<br>(Telephone Number)</center>
</td>
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<p><font size=-1>(2) Have all other periodic reports required under Section
13 or 15(d) of the Securities Exchange Act of 1934 or Section 30 of the
Investment Company Act of 1940 during the preceding 12 months or for such
shorter period that the registrant was required to file such report(s)
been filed? If the answer is no, identify report(s). [X] Yes [_] No</font>
<p><font size=-1>(3) Is it anticipated that any significant change in results
of operations from the corresponding period for the last fiscal year will
be reflected by the earnings statements to be included in the subject report
or portion thereof? [ ] Yes [X] No</font>
<p><font size=-1>If so, attach an explanation of the anticipated change,
both narratively and quantitatively, and, if appropriate, state the reasons
why a reasonable estimate of the results cannot be made.</font>
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<p><u><font size=-1>Cabletron Systems, Inc.</font></u>
<br><font size=-1>(Name of Registrant as Specified in Charter)</font></center>
<p><font size=-1>has caused this notification to be signed on its behalf
by the undersigned hereunto duly authorized.</font>
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<center><u><font size=-1>January 14, 2000</font></u>
<br><u>(Date)</u></center>
</td>
<td VALIGN=TOP WIDTH="46%"><font size=-1>By: <u>/s/ David J. Kirkpatrick</u></font>
<br><font size=-1>David J. Kirkpatrick</font>
<br><font size=-1>Corporate Executive Vice President</font>
<br><font size=-1>of Finance and Chief Financial Officer</font></td>
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