<PAGE>   1

       As filed with the Securities and Exchange Commission on March 2, 2001
                                                    Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                ---------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                                ---------------

                           COSINE COMMUNICATIONS, INC.

             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                                ---------------
<TABLE>
<S>                                                       <C>
            DELAWARE                                           94-3280301
(STATE OR OTHER JURISDICTION OF                              (I.R.S. EMPLOYER
 INCORPORATION OR ORGANIZATION)                           IDENTIFICATION NUMBER)
</TABLE>
                               3200 BRIDGE PARKWAY
                         REDWOOD CITY, CALIFORNIA 94065
                                 (650) 637-4777

          (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES, INCLUDING ZIP CODE)

                                ---------------

                                 1997 STOCK PLAN
                                 2000 STOCK PLAN
                        2000 EMPLOYEE STOCK PURCHASE PLAN
                            2000 DIRECTOR OPTION PLAN

                            (FULL TITLE OF THE PLANS)

                                ---------------

                               DEAN E.G. HAMILTON
                      PRESIDENT AND CHIEF EXECUTIVE OFFICER
                           COSINE COMMUNICATIONS, INC.
                               3200 BRIDGE PARKWAY
                         REDWOOD CITY, CALIFORNIA 94065
                                 (650) 637-4777


 (NAME, ADDRESS AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE)

                                 ---------------

                                   Copies to:
                             JOHN V. ERICKSON, ESQ.
                             COLLETTE & ERICKSON LLP
                        555 CALIFORNIA STREET, SUITE 4350
                         SAN FRANCISCO, CALIFORNIA 94104

                                 (415) 788-4646

<PAGE>   2

                         CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
========================================= ========================= ====================== ====================== ==================
                                                                          PROPOSED               PROPOSED
                                                                           MAXIMUM                MAXIMUM
                                                   AMOUNT                 OFFERING               AGGREGATE             AMOUNT OF
          TITLE OF SECURITIES                      TO BE                    PRICE                OFFERING            REGISTRATION
            TO BE REGISTERED                   REGISTERED (1)             PER SHARE                PRICE                  FEE
----------------------------------------- ------------------------- ---------------------- ---------------------- ------------------
<S>                                           <C>                   <C>                    <C>                    <C>
Common Stock,  par value $0.0001,  to be       11,705,356 shares      $ 7.3332(2)           $ 85,837,716.62(2)     $21,459.43
issued  upon  exercise  of   outstanding
options  granted  under  the 1997  Stock
Plan

Common Stock,  par value $0.0001,  to be        8,930,623 shares      $10.5318(3)           $ 94,055,535.13(3)     $23,513.88
issued under the 2000 Stock Plan

Common Stock,  par value $0.0001,  to be        4,500,000 shares      $   7.65(4)           $ 34,425,000.00(4)     $ 8,606.25
issued  under  the 2000  Employee  Stock
Purchase Plan

Common Stock,  par value $0.0001,  to be          400,000 shares      $   9.00(5)           $  3,600,000.00(5)     $   900.00
issued  under the 2000  Director  Option
Plan

TOTAL REGISTRATION FEES                        25,535,979                    __             $217,918,251.75        $54,479.56
========================================= ========================= ====================== ====================== ==================
</TABLE>

(1)  Together with an indeterminate number of additional shares which may be
     necessary to adjust the number of shares reserved for issuance pursuant to
     the plans as the result of any future stock split, stock dividend or
     similar adjustment to CoSine's outstanding common stock.

(2)  The computation is based upon the weighted average exercise price per share
     of $7.3332 as to options to purchase an aggregate of 11,705,356 shares of
     common stock granted under the 1997 Stock Plan outstanding but unexercised
     as of February 27, 2001. Pursuant to Rule 457(h)(1) of the Securities Act
     of 1933, the aggregate offering price and the fee have been computed upon
     the basis of the price at which the options may be exercised.

(3)  The computation is based upon (i) the weighted average exercise price per
     share of $15.8526 as to options to purchase an aggregate of 1,996,325
     shares of common stock granted under the 2000 Stock Plan outstanding but
     unexercised as of February 27, 2001 where, pursuant to Rule 457(h)(1) of
     the Securities Act of 1933, the aggregate offering price and the fee
     corresponding to the outstanding but unexercised options may be computed
     based upon the price at which the options may be exercised, and (ii) the
     average of the high and low prices of the common stock as reported on the
     Nasdaq National Market on February 23, 2001 as to an aggregate of 6,934,298
     shares of common stock available to be issued under the 2000 Stock Plan as
     of February 27, 2001, as estimated in accordance with Rule 457(h) under the
     Securities Act of 1933 solely for the purpose of calculating the
     registration fee.

(4)  Estimated in accordance with Rule 457(h) under the Securities Act of 1933
     solely for the purpose of calculating the registration fee. The computation
     is based upon 85% of the average of the high and low prices of the common
     stock as reported on the Nasdaq National Market on February 23, 2001
     because the purchase price of a share of common stock under the 2000
     Employee Stock Purchase Plan is equal to 85% of the fair market value of a
     share of common stock on the enrollment date or the exercise date,
     whichever is lower.

(5)  Estimated in accordance with Rule 457(h) under the Securities Act of 1933
     solely for the purpose of calculating the registration fee, based upon the
     average of the high and low prices of the common stock as reported on the
     Nasdaq National Market on February 23, 2001.


                                       2

<PAGE>   3

                                     PART II

                 INFORMATION REQUIRED IN REGISTRATION STATEMENT

ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE.


     The following documents filed by us with the Securities and Exchange
Commission, or SEC, are incorporated by reference into this registration
statement:

     (a)  Our prospectus filed on September 26, 2000, pursuant to Rule 424(b)(4)
          under the Securities Act of 1933, or Securities Act;

     (b)  The description of our common stock contained in our registration
          statement on Form 8-A (File No. 000-30715) filed on May 26, 2000, as
          amended on September 14, 2000, pursuant to Section 12(g) of the
          Securities Exchange Act of 1934, or the Exchange Act, including any
          amendments or reports filed for the purpose of updating such
          description; and

     (c)  Our quarterly report on Form 10-Q filed on November 14, 2000 for the
          quarter ended September 30, 2000.

     All documents subsequently filed by us pursuant to Section 13(a), 13(c), 14
or 15(d) of the Exchange Act, prior to the filing of a post-effective amendment
which indicates that all securities offered have been sold or which deregisters
all securities then remaining unsold, shall be deemed to be incorporated by
reference into this registration statement and to be part hereof from the date
of filing of such documents.


ITEM 4. DESCRIPTION OF SECURITIES.

     Not applicable.

ITEM 5. INTERESTS OF NAMED EXPERTS AND COUNSEL.

     Not applicable.

ITEM 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     Sections 145(a) and (b) of the Delaware General Corporation Law permit us
to indemnify any person who was or is a party or is threatened to be made a
party to any threatened, pending, or completed action, suit or proceeding,
whether civil, criminal, administrative or investigative by reason of the fact
that the person is or was one of our directors, officers, employees or agents,
or is or was serving at our request as a director, officer, employee or agent of
another enterprise, against expenses (including attorneys' fees), judgments,
fines and amounts paid in settlement actually and reasonably incurred by the
person if the person acted in good faith and in a manner the person reasonably
believed to be in or not opposed to our best interests, and, with respect to any
criminal action or proceeding, had no reasonable cause to believe the person's
conduct was unlawful; provided, that with respect to actions or suits brought on
our behalf, the person may only be indemnified with respect to expenses
(including attorneys' fees) and may not be indemnified with respect to any
claim, issue or matter for which the person is adjudged to be liable unless a
court determines otherwise. Under Section 145(c), to the extent that one of our
present or former directors or officers is successful on the merits or otherwise
in defense of any of these actions, suits or proceedings, or in defense of any
claim, issue or matter therein, the director or officer shall be indemnified
against expenses (including attorneys' fees) that the director or officer
actually and reasonably incurs because of the action, suit, or proceeding.
Section 145 of

                                       3

<PAGE>   4

the Delaware General Corporation Law permits a corporation to include in its
charter documents, and in agreements between the corporation and its directors
and officers, provisions expanding the scope of indemnification beyond that
specifically provided by the current law.

     Article XI of our certificate of incorporation requires us to indemnify our
directors, officers, employees and agents to the fullest extent permitted by
law. Article XI also requires us or our stockholders, if permitted by Delaware
law, to indemnify our directors for monetary damages for breach of fiduciary
duty as a director.

     Article VI of our bylaws requires us to indemnify our directors, officers,
employees, and agents to the extent permitted by Section 145(a) and (b) of the
Delaware General Corporation Law. Article VI also provides that, to the extent
that a director, officer, employee or agent has been successful on the merits or
otherwise in defense of any such action, suit or proceeding, or in defense of
any claim, issue or matter therein, we shall indemnify the person for his
reasonable expenses incurred because of his defense.

     In addition to the indemnification provided for in our certificate of
incorporation and bylaws, we are in the process of entering into indemnification
agreements with our existing and future directors and officers. We also have and
intend to maintain, as permitted by Article VI of our bylaws, liability
insurance for the benefit of our directors and officers.

ITEM 7. EXEMPTION FROM REGISTRATION CLAIMED.

     Not applicable.

ITEM 8. EXHIBITS.

<TABLE>
<CAPTION>
        Exhibit
         Number                            Description
        -------                            -----------
         <S>        <C>
          4.1*      Second Amended and Restated Certificate of Incorporation, as
                    amended (incorporated by reference to Exhibit 3.2 to Form 8A
                    (file no. 000-30715) filed May 26, 2000).

          4.2*      Amended and Restated Bylaws, as amended (incorporated by
                    reference to Exhibit 3.3 to Form 8A (file no. 000-30715)
                    filed May 26, 2000).

          4.3*      2000 Stock Plan and forms of agreements thereunder
                    (incorporated by reference to Exhibit 10.2 to Amendment No.
                    1 to Registration Statement on Form S-1 filed June 6, 2000).

          4.4*      2000 Employee Stock Purchase Plan and forms of agreements
                    thereunder (incorporated by reference to Exhibit 10.3 to
                    Amendment No. 1 to Registration Statement on Form S-1 filed
                    June 6, 2000).

          4.5*      2000 Director Option Plan and forms of agreements thereunder
                    (incorporated by reference to Exhibit 10.4 to Amendment No.
                    1 to Registration Statement on Form S-1 filed June 6, 2000).

          4.6*      1997 Stock Plan (as amended and restated) and forms of
                    agreements thereunder (incorporated by reference to Exhibit
                    10.5 to Amendment No. 1 to Registration Statement on Form
                    S-1 filed June 6, 2000).

          5.1       Opinion of Collette & Erickson LLP, as to legality of common
                    stock being registered.

         23.1       Consent of Ernst & Young LLP, Independent Auditors.

         23.2       Consent of Collette & Erickson LLP (contained in exhibit
                    5.1).

         24.1       Power of Attorney (see signature pages).
</TABLE>

                                       4

<PAGE>   5

*   Previously filed.

ITEM 9. UNDERTAKINGS.

     (a)  We hereby undertake:

          (1)  To file, during any period in which offers or sales are being
made, a post-effective amendment to this registration statement to include any
material information with respect to the plan of distribution not previously
disclosed in the registration statement or any material change to such
information in this registration statement.

          (2)  That, for the purpose of determining any liability under the
Securities Act, each post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

          (3)  To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

     (b)  We hereby undertake that, for purposes of determining any liability
under the Securities Act, each filing of our annual report pursuant to Section
13(a) or Section 15(d) of the Exchange Act (and, where applicable, each filing
of an employee benefit plan's annual report pursuant to Section 15(d) of the
Exchange Act) that is incorporated by reference in this registration statement
shall be deemed to be a new registration statement relating to the securities
offered therein, and the offering of such securities at that time shall be
deemed to be the initial bona fide offering thereof.

     (c)  Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to our directors, officers and controlling
persons pursuant to law, our certificate of incorporation, our bylaws or
indemnification agreements, or otherwise, we have been advised that in the
opinion of the Securities and Exchange Commission such indemnification is
against public policy as expressed in the Securities Act and is therefore
unenforceable. If a claim for indemnification against such liabilities (other
than the payment by us of expenses incurred or paid by one of our directors,
officers or controlling persons in a successful defense of any action, suit or
proceeding) is asserted by such director, officers or controlling person in
connection with the securities being registered hereunder, we will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question of whether such
indemnification by it is against public policy as expressed in the Securities
Act and will be governed by the final adjudication of such issue.

                                       5

<PAGE>   6

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this registration
statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the city of Redwood City, State of California, on March 1, 2001.



                                       COSINE COMMUNICATIONS, INC.



                                       By: /s/ Dean E. G. Hamilton
                                          --------------------------------------
                                          Dean E. G. Hamilton,
                                          President and Chief Executive Officer



                                POWER OF ATTORNEY

     KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Dean E. G. Hamilton and Craig B. Collins,
and each of them acting individually, his true and lawful attorneys-in-fact and
agents, each with full power of substitution, for him in any and all capacities,
to sign any and all amendments to this Registration Statement on Form S-8, and
to file the same, with all exhibits thereto and all other documents in
connection therewith, with the Securities and Exchange Commission, granting unto
each of said attorneys-in-fact, or his substitute or substitutes, and each of
them, full power and authority to do and perform each and every act and thing
requisite and necessary to be done to effectuate the foregoing, as fully for all
intents and purposes as he might or could do in person, hereby ratifying and
confirming all that such attorneys-in-fact, or any substitutes, may do or cause
to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed on March 1, 2001 by the following persons
in the capacities indicated.


<TABLE>
<CAPTION>
             SIGNATURE                                          TITLE
             ---------                                          -----
<S>                                         <C>

/s/ Dean E. G. Hamilton                     President, Chief Executive Officer
----------------------------------          and Director
Dean E. G. Hamilton                         (Principal Executive Officer)



/s/ Craig B. Collins                        Chief Financial Officer (Principal
----------------------------------          Financial and Accounting Officer)
Craig B. Collins



/s/ Donald Green                            Director
----------------------------------
Donald Green
</TABLE>

                                       6

<PAGE>   7

<TABLE>
<S>                                         <C>


/s/ R. David Spreng                         Director
----------------------------------
R. David Spreng



/s/ Vinton G. Cerf                          Director
----------------------------------
Vinton G. Cerf



/s/ Charles J. Abbe                         Director
----------------------------------
Charles J. Abbe
</TABLE>


                                       7

<PAGE>   8

                                INDEX TO EXHIBITS

<TABLE>
<CAPTION>
        Exhibit
         Number                            Description
        -------                            -----------
         <S>        <C>
          4.1*      Second Amended and Restated Certificate of Incorporation, as
                    amended (incorporated by reference to Exhibit 3.2 to Form 8A
                    (file no. 000-30715) filed May 26, 2000).

          4.2*      Amended and Restated Bylaws, as amended (incorporated by
                    reference to Exhibit 3.3 to Form 8A (file no. 000-30715)
                    filed May 26, 2000).

          4.3*      2000 Stock Plan and forms of agreements thereunder
                    (incorporated by reference to Exhibit 10.2 to Amendment No.
                    1 to Registration Statement on Form S-1 filed June 6, 2000).

          4.4*      2000 Employee Stock Purchase Plan and forms of agreements
                    thereunder (incorporated by reference to Exhibit 10.3 to
                    Amendment No. 1 to Registration Statement on Form S-1 filed
                    June 6, 2000).

          4.5*      2000 Director Option Plan and forms of agreements thereunder
                    (incorporated by reference to Exhibit 10.4 to Amendment No.
                    1 to Registration Statement on Form S-1 filed June 6, 2000).

          4.6*      1997 Stock Plan (as amended and restated) and forms of
                    agreements thereunder (incorporated by reference to Exhibit
                    10.5 to Amendment No. 1 to Registration Statement on Form
                    S-1 filed June 6, 2000).

          5.1       Opinion of Collette & Erickson LLP, as to legality of common
                    stock being registered.

         23.1       Consent of Ernst & Young LLP, Independent Auditors.

         23.2       Consent of Collette & Erickson LLP (contained in exhibit
                    5.1).

         24.1       Power of Attorney (see signature pages).
</TABLE>

*   Previously filed.
[{"type": "S-8", "sequence": "1", "filename": "f69138ors-8.txt", "description": "FORM S-8", "secsgml_size_bytes": 22109}]
{"company-data": {"conformed-name": "COSINE COMMUNICATIONS INC", "cik": "0001060824", "assigned-sic": "3576", "irs-number": "943280301", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-56496", "film-number": "1560677"}, "business-address": {"street1": "3200 BRIDGE PKWAY", "street2": "STE 200", "city": "REDWOOD CITY", "state": "CA", "zip": "94065", "phone": "6506374777"}, "mail-address": {"street1": "3200 BRIDGE PARKWAY", "city": "REDWOOD CITY", "state": "CA", "zip": "94065"}}
1

       As filed with the Securities and Exchange Commission on March 2, 2001
                                                    Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                ---------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                                ---------------

                           COSINE COMMUNICATIONS, INC.

             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                                ---------------
DELAWARE                                           94-3280301
(STATE OR OTHER JURISDICTION OF                              (I.R.S. EMPLOYER
 INCORPORATION OR ORGANIZATION)                           IDENTIFICATION NUMBER)
3200 BRIDGE PARKWAY
                         REDWOOD CITY, CALIFORNIA 94065
                                 (650) 637-4777

          (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES, INCLUDING ZIP CODE)

                                ---------------

                                 1997 STOCK PLAN
                                 2000 STOCK PLAN
                        2000 EMPLOYEE STOCK PURCHASE PLAN
                            2000 DIRECTOR OPTION PLAN

                            (FULL TITLE OF THE PLANS)

                                ---------------

                               DEAN E.G. HAMILTON
                      PRESIDENT AND CHIEF EXECUTIVE OFFICER
                           COSINE COMMUNICATIONS, INC.
                               3200 BRIDGE PARKWAY
                         REDWOOD CITY, CALIFORNIA 94065
                                 (650) 637-4777

 (NAME, ADDRESS AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE)

                                 ---------------

                                   Copies to:
                             JOHN V. ERICKSON, ESQ.
                             COLLETTE & ERICKSON LLP
                        555 CALIFORNIA STREET, SUITE 4350
                         SAN FRANCISCO, CALIFORNIA 94104

                                 (415) 788-4646
2

                         CALCULATION OF REGISTRATION FEE
========================================= ========================= ====================== ====================== ==================
                                                                          PROPOSED               PROPOSED
                                                                           MAXIMUM                MAXIMUM
                                                   AMOUNT                 OFFERING               AGGREGATE             AMOUNT OF
          TITLE OF SECURITIES                      TO BE                    PRICE                OFFERING            REGISTRATION
            TO BE REGISTERED                   REGISTERED (1)             PER SHARE                PRICE                  FEE
----------------------------------------- ------------------------- ---------------------- ---------------------- ------------------
Common Stock,  par value $0.0001,  to be       11,705,356 shares      $ 7.3332(2)           $ 85,837,716.62(2)     $21,459.43
issued  upon  exercise  of   outstanding
options  granted  under  the 1997  Stock
Plan

Common Stock,  par value $0.0001,  to be        8,930,623 shares      $10.5318(3)           $ 94,055,535.13(3)     $23,513.88
issued under the 2000 Stock Plan

Common Stock,  par value $0.0001,  to be        4,500,000 shares      $   7.65(4)           $ 34,425,000.00(4)     $ 8,606.25
issued  under  the 2000  Employee  Stock
Purchase Plan

Common Stock,  par value $0.0001,  to be          400,000 shares      $   9.00(5)           $  3,600,000.00(5)     $   900.00
issued  under the 2000  Director  Option
Plan

TOTAL REGISTRATION FEES                        25,535,979                    __             $217,918,251.75        $54,479.56
========================================= ========================= ====================== ====================== ==================
(1)  Together with an indeterminate number of additional shares which may be
     necessary to adjust the number of shares reserved for issuance pursuant to
     the plans as the result of any future stock split, stock dividend or
     similar adjustment to CoSine's outstanding common stock.

(2)  The computation is based upon the weighted average exercise price per share
     of $7.3332 as to options to purchase an aggregate of 11,705,356 shares of
     common stock granted under the 1997 Stock Plan outstanding but unexercised
     as of February 27, 2001. Pursuant to Rule 457(h)(1) of the Securities Act
     of 1933, the aggregate offering price and the fee have been computed upon
     the basis of the price at which the options may be exercised.

(3)  The computation is based upon (i) the weighted average exercise price per
     share of $15.8526 as to options to purchase an aggregate of 1,996,325
     shares of common stock granted under the 2000 Stock Plan outstanding but
     unexercised as of February 27, 2001 where, pursuant to Rule 457(h)(1) of
     the Securities Act of 1933, the aggregate offering price and the fee
     corresponding to the outstanding but unexercised options may be computed
     based upon the price at which the options may be exercised, and (ii) the
     average of the high and low prices of the common stock as reported on the
     Nasdaq National Market on February 23, 2001 as to an aggregate of 6,934,298
     shares of common stock available to be issued under the 2000 Stock Plan as
     of February 27, 2001, as estimated in accordance with Rule 457(h) under the
     Securities Act of 1933 solely for the purpose of calculating the
     registration fee.

(4)  Estimated in accordance with Rule 457(h) under the Securities Act of 1933
     solely for the purpose of calculating the registration fee. The computation
     is based upon 85% of the average of the high and low prices of the common
     stock as reported on the Nasdaq National Market on February 23, 2001
     because the purchase price of a share of common stock under the 2000
     Employee Stock Purchase Plan is equal to 85% of the fair market value of a
     share of common stock on the enrollment date or the exercise date,
     whichever is lower.

(5)  Estimated in accordance with Rule 457(h) under the Securities Act of 1933
     solely for the purpose of calculating the registration fee, based upon the
     average of the high and low prices of the common stock as reported on the
     Nasdaq National Market on February 23, 2001.

                                       2
3

                                     PART II

                 INFORMATION REQUIRED IN REGISTRATION STATEMENT

ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE.

     The following documents filed by us with the Securities and Exchange
Commission, or SEC, are incorporated by reference into this registration
statement:

     (a)  Our prospectus filed on September 26, 2000, pursuant to Rule 424(b)(4)
          under the Securities Act of 1933, or Securities Act;

     (b)  The description of our common stock contained in our registration
          statement on Form 8-A (File No. 000-30715) filed on May 26, 2000, as
          amended on September 14, 2000, pursuant to Section 12(g) of the
          Securities Exchange Act of 1934, or the Exchange Act, including any
          amendments or reports filed for the purpose of updating such
          description; and

     (c)  Our quarterly report on Form 10-Q filed on November 14, 2000 for the
          quarter ended September 30, 2000.

     All documents subsequently filed by us pursuant to Section 13(a), 13(c), 14
or 15(d) of the Exchange Act, prior to the filing of a post-effective amendment
which indicates that all securities offered have been sold or which deregisters
all securities then remaining unsold, shall be deemed to be incorporated by
reference into this registration statement and to be part hereof from the date
of filing of such documents.

ITEM 4. DESCRIPTION OF SECURITIES.

     Not applicable.

ITEM 5. INTERESTS OF NAMED EXPERTS AND COUNSEL.

     Not applicable.

ITEM 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     Sections 145(a) and (b) of the Delaware General Corporation Law permit us
to indemnify any person who was or is a party or is threatened to be made a
party to any threatened, pending, or completed action, suit or proceeding,
whether civil, criminal, administrative or investigative by reason of the fact
that the person is or was one of our directors, officers, employees or agents,
or is or was serving at our request as a director, officer, employee or agent of
another enterprise, against expenses (including attorneys' fees), judgments,
fines and amounts paid in settlement actually and reasonably incurred by the
person if the person acted in good faith and in a manner the person reasonably
believed to be in or not opposed to our best interests, and, with respect to any
criminal action or proceeding, had no reasonable cause to believe the person's
conduct was unlawful; provided, that with respect to actions or suits brought on
our behalf, the person may only be indemnified with respect to expenses
(including attorneys' fees) and may not be indemnified with respect to any
claim, issue or matter for which the person is adjudged to be liable unless a
court determines otherwise. Under Section 145(c), to the extent that one of our
present or former directors or officers is successful on the merits or otherwise
in defense of any of these actions, suits or proceedings, or in defense of any
claim, issue or matter therein, the director or officer shall be indemnified
against expenses (including attorneys' fees) that the director or officer
actually and reasonably incurs because of the action, suit, or proceeding.
Section 145 of

                                       3
4

the Delaware General Corporation Law permits a corporation to include in its
charter documents, and in agreements between the corporation and its directors
and officers, provisions expanding the scope of indemnification beyond that
specifically provided by the current law.

     Article XI of our certificate of incorporation requires us to indemnify our
directors, officers, employees and agents to the fullest extent permitted by
law. Article XI also requires us or our stockholders, if permitted by Delaware
law, to indemnify our directors for monetary damages for breach of fiduciary
duty as a director.

     Article VI of our bylaws requires us to indemnify our directors, officers,
employees, and agents to the extent permitted by Section 145(a) and (b) of the
Delaware General Corporation Law. Article VI also provides that, to the extent
that a director, officer, employee or agent has been successful on the merits or
otherwise in defense of any such action, suit or proceeding, or in defense of
any claim, issue or matter therein, we shall indemnify the person for his
reasonable expenses incurred because of his defense.

     In addition to the indemnification provided for in our certificate of
incorporation and bylaws, we are in the process of entering into indemnification
agreements with our existing and future directors and officers. We also have and
intend to maintain, as permitted by Article VI of our bylaws, liability
insurance for the benefit of our directors and officers.

ITEM 7. EXEMPTION FROM REGISTRATION CLAIMED.

     Not applicable.

ITEM 8. EXHIBITS.
Exhibit
         Number                            Description
        -------                            -----------
4.1*      Second Amended and Restated Certificate of Incorporation, as
                    amended (incorporated by reference to Exhibit 3.2 to Form 8A
                    (file no. 000-30715) filed May 26, 2000).

          4.2*      Amended and Restated Bylaws, as amended (incorporated by
                    reference to Exhibit 3.3 to Form 8A (file no. 000-30715)
                    filed May 26, 2000).

          4.3*      2000 Stock Plan and forms of agreements thereunder
                    (incorporated by reference to Exhibit 10.2 to Amendment No.
                    1 to Registration Statement on Form S-1 filed June 6, 2000).

          4.4*      2000 Employee Stock Purchase Plan and forms of agreements
                    thereunder (incorporated by reference to Exhibit 10.3 to
                    Amendment No. 1 to Registration Statement on Form S-1 filed
                    June 6, 2000).

          4.5*      2000 Director Option Plan and forms of agreements thereunder
                    (incorporated by reference to Exhibit 10.4 to Amendment No.
                    1 to Registration Statement on Form S-1 filed June 6, 2000).

          4.6*      1997 Stock Plan (as amended and restated) and forms of
                    agreements thereunder (incorporated by reference to Exhibit
                    10.5 to Amendment No. 1 to Registration Statement on Form
                    S-1 filed June 6, 2000).

          5.1       Opinion of Collette & Erickson LLP, as to legality of common
                    stock being registered.

         23.1       Consent of Ernst & Young LLP, Independent Auditors.

         23.2       Consent of Collette & Erickson LLP (contained in exhibit
                    5.1).

         24.1       Power of Attorney (see signature pages).
4
5

*   Previously filed.

ITEM 9. UNDERTAKINGS.

     (a)  We hereby undertake:

          (1)  To file, during any period in which offers or sales are being
made, a post-effective amendment to this registration statement to include any
material information with respect to the plan of distribution not previously
disclosed in the registration statement or any material change to such
information in this registration statement.

          (2)  That, for the purpose of determining any liability under the
Securities Act, each post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

          (3)  To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

     (b)  We hereby undertake that, for purposes of determining any liability
under the Securities Act, each filing of our annual report pursuant to Section
13(a) or Section 15(d) of the Exchange Act (and, where applicable, each filing
of an employee benefit plan's annual report pursuant to Section 15(d) of the
Exchange Act) that is incorporated by reference in this registration statement
shall be deemed to be a new registration statement relating to the securities
offered therein, and the offering of such securities at that time shall be
deemed to be the initial bona fide offering thereof.

     (c)  Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to our directors, officers and controlling
persons pursuant to law, our certificate of incorporation, our bylaws or
indemnification agreements, or otherwise, we have been advised that in the
opinion of the Securities and Exchange Commission such indemnification is
against public policy as expressed in the Securities Act and is therefore
unenforceable. If a claim for indemnification against such liabilities (other
than the payment by us of expenses incurred or paid by one of our directors,
officers or controlling persons in a successful defense of any action, suit or
proceeding) is asserted by such director, officers or controlling person in
connection with the securities being registered hereunder, we will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question of whether such
indemnification by it is against public policy as expressed in the Securities
Act and will be governed by the final adjudication of such issue.

                                       5
6

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this registration
statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the city of Redwood City, State of California, on March 1, 2001.

                                       COSINE COMMUNICATIONS, INC.

                                       By: /s/ Dean E. G. Hamilton
                                          --------------------------------------
                                          Dean E. G. Hamilton,
                                          President and Chief Executive Officer

                                POWER OF ATTORNEY

     KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Dean E. G. Hamilton and Craig B. Collins,
and each of them acting individually, his true and lawful attorneys-in-fact and
agents, each with full power of substitution, for him in any and all capacities,
to sign any and all amendments to this Registration Statement on Form S-8, and
to file the same, with all exhibits thereto and all other documents in
connection therewith, with the Securities and Exchange Commission, granting unto
each of said attorneys-in-fact, or his substitute or substitutes, and each of
them, full power and authority to do and perform each and every act and thing
requisite and necessary to be done to effectuate the foregoing, as fully for all
intents and purposes as he might or could do in person, hereby ratifying and
confirming all that such attorneys-in-fact, or any substitutes, may do or cause
to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed on March 1, 2001 by the following persons
in the capacities indicated.
SIGNATURE                                          TITLE
             ---------                                          -----
/s/ Dean E. G. Hamilton                     President, Chief Executive Officer
----------------------------------          and Director
Dean E. G. Hamilton                         (Principal Executive Officer)

/s/ Craig B. Collins                        Chief Financial Officer (Principal
----------------------------------          Financial and Accounting Officer)
Craig B. Collins

/s/ Donald Green                            Director
----------------------------------
Donald Green
6
7
/s/ R. David Spreng                         Director
----------------------------------
R. David Spreng

/s/ Vinton G. Cerf                          Director
----------------------------------
Vinton G. Cerf

/s/ Charles J. Abbe                         Director
----------------------------------
Charles J. Abbe
7
8

                                INDEX TO EXHIBITS
Exhibit
         Number                            Description
        -------                            -----------
4.1*      Second Amended and Restated Certificate of Incorporation, as
                    amended (incorporated by reference to Exhibit 3.2 to Form 8A
                    (file no. 000-30715) filed May 26, 2000).

          4.2*      Amended and Restated Bylaws, as amended (incorporated by
                    reference to Exhibit 3.3 to Form 8A (file no. 000-30715)
                    filed May 26, 2000).

          4.3*      2000 Stock Plan and forms of agreements thereunder
                    (incorporated by reference to Exhibit 10.2 to Amendment No.
                    1 to Registration Statement on Form S-1 filed June 6, 2000).

          4.4*      2000 Employee Stock Purchase Plan and forms of agreements
                    thereunder (incorporated by reference to Exhibit 10.3 to
                    Amendment No. 1 to Registration Statement on Form S-1 filed
                    June 6, 2000).

          4.5*      2000 Director Option Plan and forms of agreements thereunder
                    (incorporated by reference to Exhibit 10.4 to Amendment No.
                    1 to Registration Statement on Form S-1 filed June 6, 2000).

          4.6*      1997 Stock Plan (as amended and restated) and forms of
                    agreements thereunder (incorporated by reference to Exhibit
                    10.5 to Amendment No. 1 to Registration Statement on Form
                    S-1 filed June 6, 2000).

          5.1       Opinion of Collette & Erickson LLP, as to legality of common
                    stock being registered.

         23.1       Consent of Ernst & Young LLP, Independent Auditors.

         23.2       Consent of Collette & Erickson LLP (contained in exhibit
                    5.1).

         24.1       Power of Attorney (see signature pages).
*   Previously filed.