<TABLE> <S> <C>
<PAGE>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY INFORMATION EXTRACTED FROM THE CONSOLIDATED
BALANCE SHEET, CONSOLIDATED STATEMENT OF OPERATIONS AND THE CONSOLIDATED
STATEMENT OF CASH FLOWS INCLUDED IN THE COMPANY'S FORM 10-Q FOR THE NINE MONTHS
ENDED DECEMBER 2, 2000 AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIAL STATEMENTS.
</LEGEND>
<CIK> 0000846909
<NAME> CABLETRON SYSTEMS, INC.
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> 9-MOS
<FISCAL-YEAR-END> MAR-03-2001
<PERIOD-START> MAR-01-2000
<PERIOD-END> DEC-02-2000
<CASH> 251,763
<SECURITIES> 238,205
<RECEIVABLES> 195,829
<ALLOWANCES> 24,487
<INVENTORY> 89,024
<CURRENT-ASSETS> 967,927
<PP&E> 344,240
<DEPRECIATION> 250,946
<TOTAL-ASSETS> 1,693,570
<CURRENT-LIABILITIES> 518,848
<BONDS> 0
0
70,966
<COMMON> 1,866
<OTHER-SE> 1,083,108
<TOTAL-LIABILITY-AND-EQUITY> 1,693,570
<SALES> 785,437
<TOTAL-REVENUES> 785,437
<CGS> 417,746
<TOTAL-COSTS> 417,746
<OTHER-EXPENSES> 888,386
<LOSS-PROVISION> 0
<INTEREST-EXPENSE> (27,238)
<INCOME-PRETAX> (255,983)
<INCOME-TAX> (181,177)
<INCOME-CONTINUING> (181,177)
<DISCONTINUED> 0
<EXTRAORDINARY> 0
<CHANGES> 0
<NET-INCOME> (201,038)
<EPS-BASIC> (1.09)
<EPS-DILUTED> (1.09)
</TABLE>