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                                                                     EXHIBIT 5.1


                                 March 17, 1997



Internet Middleware Corporation
50 Airport Parkway
San Jose, CA  95110

Ladies and Gentlemen:

                 We have acted as counsel for Network Appliance, Inc., a
California corporation ("Acquiror"), in connection with the merger (the
"Merger") of Internet Middleware Corporation, a California corporation
("Target"), with and into Acquiror pursuant to the Agreement and Plan of
Reorganization by and between Acquiror and Target, dated as of March 17, 1997
(the "Reorganization Agreement"), and the Agreement of Merger between Acquiror
and Target, dated as of March 17, 1997 (the "Merger Agreement").  This opinion
is rendered to you pursuant to Section 6.2(c) of the Reorganization Agreement.
Capitalized terms used herein and not otherwise defined shall have the same
meaning given to such terms in the Reorganization Agreement.

                 In connection with this opinion, we have examined originals,
or copies certified or otherwise identified to our satisfaction, of such
documents, corporate records, certificates, including certificates of public
officials, and other instruments as we have deemed necessary or advisable for
purposes of this opinion, including the Restated Articles of Incorporation and
Bylaws of Acquiror and the records of its Board of Directors relating to the
Merger.  In addition, in connection with the Merger, we have reviewed the
Reorganization Agreement, the Merger Agreement and the Shareholder's Agreements
between certain Target shareholders and Acquiror.

                 In such examination and review we have assumed the genuineness
of all signatures, the legal capacity of natural persons, the authenticity of
all documents submitted to us as originals, the conformity to original
documents of all documents submitted to us as certified or photostatic copies,
and the authenticity of the originals of such copies; and that there are no
extrinsic agreements or understandings among the parties to the Reorganization
Agreement and the Merger Agreement that would modify or interpret the terms of
the Reorganization Agreement and the Merger Agreement or the respective rights
or obligations of the parties thereunder.  As to any facts material to the
opinions hereinafter expressed which we did not independently establish or
verify, we have relied without investigation, upon certificates, statements and
representations of representatives of Acquiror.  During the course of our
discussion with such officers and representatives and our review of the
documents described above in connection with the preparation of these opinions,
no facts were disclosed to us that caused us to conclude that any
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March 17, 1997
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such certificate, statement or representation is untrue.  In making our
examination of the documents executed by entities other than Acquiror, we have
assumed that each such other entity had the power to enter into and perform all
its obligations thereunder and the due authorization, execution and delivery of
such documents by each such entity.

                 The opinions hereinafter expressed are qualified to the extent
that (a) the validity or enforceability of any of the agreements, documents or
obligations referred to herein may be subject to or affected by applicable
bankruptcy, insolvency, reorganization, moratorium or other laws relating to or
affecting the rights and remedies of creditors generally, and (b) the
enforceability of such agreements, documents or obligations may be limited by
general principles of equity, including, without limitation, concepts of
materiality, reasonableness, good faith and fair dealing, and public policy,
whether applied by a court of law or equity.  We do not express any opinion
herein as to the availability of any equitable or other specific remedy upon
breach of any of the agreements, documents or obligations referred to herein.
We render or imply no opinion with respect to compliance with applicable
anti-fraud statutes, rules or regulations of applicable state or Federal law.

                 Based upon and subject to the foregoing, and subject to the
further assumptions, limitations, qualifications, and exceptions set forth
herein, we are of the opinion that:

                 1.       Acquiror is a corporation duly organized, validly
existing and in good standing under the laws of the State of California, has
the corporate power and authority to own, operate and lease its properties and
carry on its business as now conducted;

                 2.       The authorized capital stock of Acquiror consists of
55,000,000 shares of Common Stock, no par value, and 5,000,000 shares of
Preferred Stock, no par value.  At the close of business on March 14, 1997, no
shares of Preferred Stock were issued and outstanding.  At the close of
business on March 14, 1997, 15,753,147 shares of Common Stock were issued and
outstanding, all of which have been duly authorized and are validly issued,
fully paid and nonassessable.  On the close of business on March 14, 1997,
2,148,351 shares of Common Stock were subject to issuance upon exercise of
outstanding options;

                 3.       Acquiror has full corporate power and authority to
execute, deliver, and perform its obligations under the Reorganization
Agreement and the Merger Agreement; Acquiror has taken all requisite corporate
action to approve and adopt the Reorganization Agreement and the Merger
Agreement and to approve and to authorize the carrying out of the transactions
contemplated thereunder; and the Reorganization Agreement and the Merger
Agreement have been duly executed and delivered by Acquiror and constitute
legal, valid and binding obligations of Acquiror; provided that enforceability
of the indemnity obligations contained in such agreements may be limited by
public policy;
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March 17, 1997
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                 4.       The approval of the shareholders of Acquiror is not
required for the consummation of the transactions contemplated by the
Reorganization Agreement and the Merger Agreement; the shares of Acquiror
Common Stock to be delivered in exchange for shares of Target Common Stock
will, when issued as contemplated by the Reorganization Agreement and the
Merger Agreement, be validly issued, fully paid and non-assessable;

                 5.       The execution, delivery and performance of the
Reorganization Agreement by Acquiror, the execution and delivery of the Merger
Agreement by Acquiror and the carrying out of the transactions contemplated by
the Reorganization Agreement and by the Merger Agreement to be carried out by
Acquiror did not and will not conflict with or constitute a violation under the
charter documents of Acquiror;

                 6.       To our knowledge, no suit, action or legal,
administrative, arbitration or other proceeding or governmental investigation
is pending or threatened to which Acquiror or any of its assets or properties
is a party which seeks to prohibit, restrain or enjoin the transactions
contemplated by the Reorganization Agreement or the Merger Agreement;

                 7.       There is no consent, approval, authorization, order,
registration, qualification or filing of or with any court or any regulatory
authority or other governmental body (either foreign or domestic) required by
Acquiror or with respect to its assets or properties or otherwise for the
consummation of the transactions contemplated by the Reorganization Agreement
and the Merger Agreement that has not been obtained, except for (i) such
consents, approvals, authorizations, registration or qualifications as may be
required under state securities or Blue Sky laws in connection with the offer
and sale of Acquiror Common Stock pursuant to the Merger, and (ii) acceptance
for filing of the Merger Agreement together with any appropriate tax clearance
certificate by the California Secretary of State.  Our opinion herein, however,
is subject to the timely and proper completion of all filings and other actions
contemplated above in this paragraph 8 where such filings and actions are to be
undertaken on or after the date hereof; and

                 8.       Based in part upon the representations of Target
shareholders in shareholder questionnaires, the shares of Acquiror Common Stock
to be issued and delivered in exchange for shares of Target Common Stock
pursuant to the Reorganization Agreement and the Merger Agreement will, when
issued, be exempt from registration under Section 5 of the Securities Act of
1933, as amended (the "Act") pursuant to Section 4(2) of the Act.

                 Whenever our opinion herein with respect to the existence or
absence of facts is indicated to be based upon our knowledge, such expression
means that in the course of our representation of Acquiror in connection with
the Merger nothing has come to our attention that would give us actual
knowledge of the existence or absence of such facts.  We have undertaken
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March 17, 1997
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no independent factual investigation to determine the existence or absence of
such facts.

                 With respect to the opinions set forth in the third and fourth
sentences of paragraph (2) as to the number of issued and outstanding shares of
Common Stock and to the effect that such shares have been validly issued and
are fully paid and nonassessable, and as to the number of shares of Common
Stock subject to outstanding options, we have:  (i) relied, without independent
verification, on a certificate of the transfer agent and registrar of Acquiror
("Transfer Agent") dated as of March 17, 1997 as to the matters set forth
therein and (ii) relied, without independent verification, on a certificate of
an officer of Acquiror, dated as of March 17, 1997 with respect to certain of
the factual matters set forth therein.  We note, however, that we have not (x)
reviewed Acquiror's stock records, (y) verified procedures used by or obtained
records from Acquiror's Transfer Agent, or (z) independently verified that each
issued and outstanding share of Common Stock has been fully paid.

                 This opinion relates solely to the laws of the State of
California and applicable Federal laws of the United States, and we express no
opinion with respect to the effect or applicability of the laws of other
jurisdictions.

                 The opinions expressed herein are solely for your benefit in
connection with the above transactions and may not be relied upon in any manner
or for any purpose by any other person.

                                        Sincerely,



                                        BROBECK, PHLEGER & HARRISON LLP
