<PAGE>   1


                       SECURITIES AND EXCHANGE COMMISSION
                              Washington, DC 20549


                                  FORM 10-Q/A


               Quarterly Report Pursuant to Section 13 or 15(d) of
                       the Securities Exchange Act of 1934

                    For the Quarter Ended September 30, 1996

                         Commission File Number 0-20110


                              CROSSCOMM CORPORATION
                              ---------------------
             (Exact name of registrant as specified in its charter)

             DELAWARE                                              52-1513201
             --------                                              ----------
 (State or other jurisdiction                                  (I.R.S. Employer
of incorporation or organization)                                   I.D. No.)

450 DONALD LYNCH BOULEVARD, MARLBOROUGH, MASSACHUSETTS                01752
------------------------------------------------------             ----------
       (Address of principal executive office)                     (Zip Code)

                                 (508)-481-4060
                                 --------------
              (Registrant's telephone number, including area code)


Indicate by check mark whether registrant (1) has filed all reports required to
be filed by Section 13 or 15 (d) of the Securities Exchange Act of 1934 during
the preceding 12 months ( or for such shorter period that the registrant was
required to file such reports ) and (2) has been subject to such filing
requirements for the past 90 days.  YES X   No
                                       ---    ---


Indicate the number of shares outstanding of each of the registrant's classes of
common stock, as of the latest practicable date.

           CLASS                               OUTSTANDING AT NOVEMBER 1ST, 1996
           -----                               ---------------------------------

Common stock, $.01 par value                           9,196,361  shares


<PAGE>   2



                      MANAGEMENT'S DISCUSSION AND ANALYSIS
                OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

RESULTS OF OPERATIONS

Revenue
-------

The Company's product revenue increased by 5% from $7,747,000 for the three
months ended September 30, 1995 to $8,151,000 for the three months ended
September 30, 1996 and decreased by 9% from $27,869,000 to $25,238,000 for the
nine month periods ending September 30, 1995 and 1996, respectively. The
increase in product revenue for the three months ended September 30, 1996
compared to the same period in 1995 is primarily attributable to revenues from
the Company's asynchronous transfer mode ("ATM") and local area network ("LAN")
switching products more than offsetting the decline in router product revenue.
Both router volume and average selling prices of router products have declined.
The decline in product revenue for the nine months ended September 30, 1996
compared to the same period in 1995 is due primarily to the decline in sales of
the Company's router products and the later than expected introduction of the
Company's new switching products.

The Company believes that future product revenue levels are highly dependent on
its ability to successfully complete and market ATM products, its ability to
expand and capitalize on new indirect and international sales channels, its
ability to bring other new products and product features to market on a timely
basis, and upon stability within the Company's direct sales force.

Service revenue (i.e. maintenance and support contracts, billable product
repairs, customer training and product installations) increased by 18% from
$2,301,000 for the three months ended September 30, 1995 to $2,714,000 for the
three months ended September 30, 1996 and increased by 17% from $6,914,000 to
$8,087,000 for the nine months ended September 30, 1995 and 1996, respectively .
This growth is attributable to increases in the number of installed units and
the Company's increased emphasis on the sale and marketing of services.

International revenues accounted for 41% and 37% of total revenues for the three
and nine month periods ended September 30, 1996, respectively, versus 31% and
25% of total revenues for the three and nine month periods ended September 30,
1995, respectively. The increase for the comparable three month periods is
primarily attributable to increased revenues from the Company's distributors in
Europe and its indirect channel in Canada. In addition to the above factors, the
Company's subsidiary in the United Kingdom also contributed to the increase in
international revenue for the comparable nine month periods ended September 30,
1996 and 1995. The Company believes that international sales will represent a
significant portion of the Company's revenues. However, the percentage of total
revenues derived from international sales may continue to fluctuate based on
changes in domestic revenues versus international revenues, the timing of orders
from international distributors and the addition of new international
distributors.


                                       9
<PAGE>   3


                                   SIGNATURES


Pursuant to the requirements of the Securities Exchange Act of 1934, the
Registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.


                                  CROSSCOMM CORPORATION






Date: November 21, 1996           By:  /s/ Douglas G. Bryant
     ------------------               ------------------------------------------
                                      Douglas G. Bryant
                                      Chief Financial Officer
                                      (Principal Financial & Accounting Officer)



                                       16