EXHIBIT 10.25

PROMISSORY NOTE

For value received on April 12, 2000, Piyush
   Patel (hereinafter "Executive") promises to pay to the order
   of Cabletron Systems, Inc., or any of its subsidiaries (hereinafter
   "Company" or "Cabletron"), the principal sum of $385,000
   Dollars (the "Loan Amount"). The outstanding principal amount of
   this Note, along with interest accruing at a rate of 6.46% per annum, shall
   be payable at 35 Industrial Way, Rochester New Hampshire, 03866, on the
   earlier of: (i) two years from the above stated date; and (ii) as described
   in the following sentence. Upon any sale by the Executive of any shares of
   Cabletron common stock within two years following the date of this
   Promissory Note, the Executive shall repay Cabletron an amount equal to the
   net proceeds of the sale (after tax) or the total remaining unpaid,
   whichever is less.

In the event: (i) the Executive's employment with
   Cabletron is terminated by the Company without cause, or (ii) the death of
   the Executive, the entire remaining unpaid principal shall be forgiven.
   "Cause" shall mean a criminal felony, crimes of moral turpitude,
   deliberate harm of Cabletron, including fraud or embezzlement, and gross and
   repeated failure (after written notice) to perform Executive's
   duties.

To secure Executive's prompt, punctual and faithful
   performance of each of Executive's obligations under this Note, Executive
   hereby assigns to Cabletron all rights of Executive to property, monies and
   credits for which Cabletron is obligated to Executive, and which is in the
   possession of Cabletron or any affiliate or subsidiary at the time of
   default by Executive under this Note and at any time after such default,
   which property, monies and credits shall include, without limitations,
   salary, bonuses, vacation pay, and insurance proceeds. The term
   "Collateral" shall refer to all interest of Executive assigned to
   Cabletron pursuant to this paragraph.

In the event of a default by Executive under this Note,
   Cabletron shall be permitted to apply the Collateral toward the Executive's
   liabilities under this Note, and Executive hereby waives notice of
   nonpayment, demand, presentment, protest and all forms of demand and notice.
   The Executive shall remain liable to Cabletron for any deficiency remaining
   following such applications.

This Note shall be in default upon the occurrence of
   any of the following:

1. Executive fails to pay all principal owed under this
   Note when due, and such failure continues uncured for fifteen (15)
   days;
2. The Executive shall (i) admit in writing his inability
   to pay his debts generally as they become due, (ii) file a petition to
   answer seeking reorganization or arrangement of the federal bankruptcy laws
   or any other applicable law or statute of the United States of America or
   any state thereof, or any other jurisdiction, (iii) make an assignment or
   other arrangement for the benefit of his creditors generally, (iv) consent
   to the appointment of a receiver of himself, or (v) have an order for relief
   in bankruptcy entered against or with respect to him, provided such order
   shall not be vacated, set aside or stayed within thirty (30) days after the
   date of entry thereof.

If this Note is in default, the entire outstanding
   principal balance on this Note shall become immediately due and payable,
   without further notice. Should any part of the principal amount be collected
   after default by law or through an attorney-at-law, the Company shall be
   entitled to collect from the Executive, in addition to the default amount,
   all attorney fees, together with all other costs of collection.

All rights, powers, and remedies provided for herein
   are cumulative and nonexclusive. The failure or delay of the holder to
   exercise a right, power, or remedy hereunder shall not operate as a waiver
   thereof of the same or any other right, power, or remedy on any future
   occasion.

This Note, and all rights, powers, remedies and
   obligations arising from this Note, shall be construed according to and
   governed by the laws of the State of New Hampshire.

IN WITNESS WHEREOF, the Executive has hereunto set his
   hand and seal effective the date first above written

|Executive       | Cabletron Systems, Inc.         
|--------------- | --------------------------------
|                |                                 
|/s/Piyush Patel | /s/David Kirkpatrick            
|Piyush Patel    | David Kirkpatrick               
|                | Executive Vice President and CFO
|                |                                 
|4/12/00         | 4/12/00                         
|Date            | Date                            
|                |