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                                                                     EXHIBIT 4.3

Number                                                                 Shares
------                                                                 ------

 --                                                                      --


                            CABLETRON SYSTEMS, INC.

             Series B Convertible Preferred Stock, $1.00 Par Value

      SEE REVERSE SIDE FOR RESTRICTIONS ON TRANSFER AND CLASSES OF STOCK

     This certifies that -SPECIMEN- is the owner of -ZERO- shares, fully paid
and non-assessable, of the Series B Convertible Preferred Stock of CABLETRON
SYSTEMS, INC., a Delaware corporation, transferable only on the books of the
corporation by the holder hereof in person or by attorney upon surrender of this
certificate properly endorsed.

     This certificate and the shares represented hereby are subject to the
General Corporation Law of the State of Delaware and to the Certificate of
Incorporation and the By-laws of the corporation, in each case as from time to
time amended.

     IN WITNESS WHEREOF, CABLETRON SYSTEMS, INC. has caused this certificate to
be signed by its duly authorized officers and its corporate seal to be hereto
affixed this __ day of __________.



--------------------------------               ---------------------------------
An one of Chairman,                            Any one of Treasurer,
Vice Chairman, President or Vice               Assistant Treasurer, Secretary or
President                                      Assistant Secretary

                                    [SEAL]
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                           RESTRICTIONS ON TRANSFER
                           ------------------------
     The Securities represented hereby have not been registered under the
Securities Act of 1933, as amended (the "Act"), and may not be offered, sold or
otherwise transferred, assigned, pledged or hypothecated unless and until
registered under the Act or unless the Corporation has received an opinion of
counsel satisfactory to the Corporation and its counsel that such registration
is not required.

     The holder of the securities represented by this certificate is subject to
certain obligations contained in a Standstill Agreement dated as of August 29,
2000, a copy of which is available for inspection at the principal office of the
issuer hereof, and will be furnished without charge to the holder of such
securities upon written request.

                                  ASSIGNMENT
                                  ----------

     For value received, the undersigned hereby sells, assigns and transfers to
______________________________  __________________ shares of the capital stock
represented by this certificate, and does hereby irrevocably constitute and
appoint _________________________________ attorney to transfer such stock on the
books ___________________________________ with full power of substitution in the
premises.

Dated _____________________

                           Signature of registered owner corresponding exactly
                           to the name of such owner as written on the face of
                           this certificate.


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