Exhibit 5.1

                                 March __, 2002

Brocade Communications Systems, Inc.
1745 Technology Drive
San Jose, CA 95110

         Re:      Registration Statement on Form S-3

Ladies and Gentlemen:

         We have acted as counsel for Brocade Communications Systems, Inc., a
Delaware corporation (the "Company") in connection with the registration under
the Securities Act of 1933, as amended, of $550,000,000 aggregate principal
amount of 2% Convertible Subordinated Notes due 2007 (the "Notes"), and such
indeterminate number of shares of common stock, $0.001 par value, of the
Company, as may be required for issuance upon conversion of the Notes (the
"Conversion Shares"). The Notes and the Conversion Shares are to be offered and
sold by certain securityholders of the Company. In this regard we have
participated in the preparation of a Registration Statement on Form S-3
relating to the Notes and the Conversion Shares (such Registration Statement,
as it may be amended from time to time, is herein referred to as the
"Registration Statement").

         We are of the opinion that the Notes have been duly authorized and are
binding obligations of the Company entitled to the benefits of the Indenture
dated as of December 21, 2001, between the Company and State Street Bank and
Trust Company of California, N.A., as Trustee, subject to the following:

                  (a) We express no opinion as to (i) the effect of any
bankruptcy, insolvency, reorganization, arrangement, fraudulent conveyance,
moratorium or other similar laws relating to or affecting the rights of
creditors generally, including, without limitation, laws relating to fraudulent
transfers or conveyances and preferences, (ii) rights to indemnification and
contribution contained in the Notes, the Indenture and the Registration Rights
Agreement dated as of December 21, 2001 between the Company and Morgan Stanley
& Co. Incorporated, Goldman, Sachs & Co., Salomon Smith Barney, Inc. and
Merrill Lynch, Pierce Fenner and Smith Incorporated (the "Registration Rights
Agreement"), which may be limited by applicable law or equitable principles, or
(iii) the effect of general principles of equity, including without limitation,
concepts of materiality, reasonableness, good faith and fair dealing, and the
possible unavailability of specific performance, injunctive relief or other
equitable relief, and limitations on rights of acceleration regardless of
whether considered in a proceeding in equity or at law.

                  (b) We express no opinion with respect to the validity,
binding nature or enforceability of (i) any vaguely or broadly stated waiver
contained in the Notes, the Indenture and the Registration Rights Agreement,
including without limitation, the waivers of diligence, presentment, demand,
protest or notice, (ii) any provisions of any Agreements imposing



Brocade Communications Systems, Inc.
March __, 2002
Page 2

penalties or forfeitures, late payment charges or any increase in interest rate
(other than Liquidated Damages under the Registration Rights Agreement), upon
delinquency in payment or the occurrence of a default to the extent they
constitute a penalty or forfeiture or are otherwise contrary to the public
policy (iii) any provision of the Notes, the Indenture and the Registration
Rights Agreement to the effect that a statement, certificate, determination or
record shall be deemed conclusive absent manifest error (or similar effect),
including, without limitation, that any such statement, certificate,
determination or record shall be deemed conclusive absent manifest error (or
similar effect), including, without limitation, that any such statement,
certificate, determination or record shall be prima facie evidence of a fact,
or (iv) any provision of the Notes, the Indenture and the Registration Rights
Agreement which provides that notice not actually received may be binding on
any party.

                  (c) We express no opinion with respect to the legality,
validity, binding nature or enforceability of any provision of the Notes, the
Indenture and the Registration Rights Agreement to the effect that rights or
remedies are not exclusive, that every right or remedy is cumulative and may be
exercised in addition to any other right or remedy, that the election of some
particular remedy or remedies does not preclude recourse to one or more other
remedies or that failure to exercise or delay in exercising rights or remedies
will not operate as a waiver of any such right or remedy.

                  (d) We express no opinion as to any provision of the Notes,
the Indenture and the Registration Rights Agreement requiring written
amendments or waivers of such documents insofar as it suggests that oral or
other modifications, amendments or waivers could not be effectively agreed upon
by the parties or that the doctrine of promissory estoppel might not apply.

                  (e) The extent that the obligations of the Company under the
Indenture may be dependent upon such matters, we assume for purposes of this
opinion that the Trustee under the Indenture has been duly organized, is
validly existing and is in good standing under the laws of its jurisdiction of
organization; that the Trustee is duly qualified to engage in the activities
contemplated by the Indenture; that the Indenture has been duly authorized,
executed and delivered by the Trustee and constitutes a legally valid, binding
and enforceable obligation of the Trustee enforceable against the Trustee in
accordance with its terms; that the Trustee is in compliance, generally and
with respect to acting as trustee under the Indenture, with all applicable laws
and regulations; and that the Trustee has the requisite organizational and
legal power and authority to perform its obligations under the Indenture.

                  (f) This opinion speaks only at and as of its date and is
based solely on the facts and circumstance known to us at and as of such date.
We express no opinion as to the effect on rights under the Agreements of any
statute, rule, regulation or other law which is enacted or becomes effective
after, or of any court decision which changes the law relevant to such rights



Brocade Communications Systems, Inc.
March __, 2002
Page 3

which is rendered after, the date of this opinion or the conduct of the parties
following the closing of the contemplated transaction. In addition, in
rendering this opinion, we assume no obligation to revise or supplement this
opinion should the present laws of the jurisdictions mentioned herein be
changed by legislative action, judicial decision or otherwise.

         We are of the further opinion that the Conversion Shares have been
duly authorized and, when issued by the Company upon conversion of the Notes in
accordance with the terms of the Indenture, will be legally issued, fully paid
and nonassessable.

         We hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement and to the use of our name under the caption "Legal
Matters" in the Registration Statement and the Prospectus included therein. In
giving such consent, we do not consider that we are "experts" within the
meaning of such term as used in the Securities Act, or the rules and
regulations of the Securities and Exchange Commission issued thereunder, with
respect to any part of the Registration Statement, including this opinion as an
exhibit or otherwise.

                                           Sincerely,

                                           WILSON SONSINI GOODRICH & ROSATI
                                           Professional Corporation