<PAGE>

                                                                   Exhibit 10.38
                                                                   -------------

                                 PROMISSORY NOTE

     For value received on June 15, 2000, David Kirkpatrick (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
$125,000 Dollars (the "Loan Amount"). The outstanding principal amount of this
Note shall be payable at 35 Industrial Way, Rochester New Hampshire, 03866, on
the earlier of: (i) February 28, 2002; and (ii) as described in the following
sentence. Upon any sale by the Executive of any shares of Cabletron common stock
prior to February 28, 2002, the Executive shall repay Cabletron an amount equal
to the net proceeds of the sale (after tax) or the total remaining unpaid
principal (taking into account any forgiveness that has occurred pursuant to the
following paragraph), whichever is less.

     Upon completion of continuous employment by the Executive from the date of
this Promissory Note to February 28, 2001, Cabletron shall forgive the lesser of
(i) 25 percent of the Loan Amount; and (ii) the remaining unpaid principal. Upon
completion of continuous employment by the Executive from the date of this
Promissory Note to February 28, 2002, Cabletron shall forgive the lesser of (i)
75 percent of the Loan Amount; and (ii) the remaining unpaid principal. Any
amount of this Note forgiven by the Company will be reported to the Executive as
taxable wages.

     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;

                                       1
<PAGE>

     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/ David Kirkpatrick                            /s/ Piyush Patel
----------------------------                     -------------------------
David Kirkpatrick                                Piyush Patel
                                                 CEO and President

6/15/2000                                        6/15/2000
----------------------------                     -------------------------
Date                                             Date

                                       2