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                                                                     EXHIBIT 5.1

                                December 20, 2000

Juniper Networks, Inc.
1194 North Mathilda Avenue
Sunnyvale, CA 94089

     Re:  Registration Statement on Form S-3

Ladies and Gentlemen:

     I have examined the Registration Statement on Form S-3 to be filed by
Juniper Networks, Inc. (the "Company") with the Securities and Exchange
Commission on December 20, 2000 (the "Registration Statement"), in connection
with the registration under the Securities Act of 1933, as amended, of 828,351
shares of the Company's common stock (the "Shares"), all of which are authorized
and have been previously issued to the selling stockholders named therein in
connection with the acquisition by the Company of Micro Magic, Incorporated. The
Shares are to be offered by the selling stockholders for sale to the public as
described in the Registration Statement.

     I am of the opinion that all proper corporate proceedings have been taken
prior to the registration of the Shares, including such proceedings to be
carried out in accordance with the securities laws of the various states, where
required, such that the Shares, when sold in the manner referred to in the
Registration Statement, will be legally and validly issued, fully paid and
nonassessable.

     I hereby consent to the filing of this opinion with the Securities and
Exchange Commission in connection with the registration statement referred to
above. This opinion is limited to the laws of the State of Delaware and the
federal law of the United States of America.

                                       Very truly yours,


                                       /s/ Lisa C. Berry
                                       --------------------------
                                       Lisa C. Berry
                                       Vice President, General Counsel
                                       and Secretary