<PAGE>

                                                                  EXHIBIT 10.36

                               PROMISSORY NOTE

        For value received on April 12, 2000, Romulus Pereira (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 $400,000 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 two years from
the above stated date.

        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
<PAGE>

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 goverened 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/ Romulus Pereira                     /s/ David Kirkpatrick
----------------------------            ----------------------------
Romulus Pereira                         David Kirkpatrick
                                        Executive Vice President and CFO


-------------                           -------------
Date                                    Date








                                      2