
<PAGE>   1

                                                                       EXHIBIT 5

                                    EXHIBIT 5

             OPINION AND CONSENT OF BROBECK, PHLEGER & HARRISON LLP



                                 March 12, 2001


Cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134-1706

        Re:     Cisco Systems, Inc. -- Registration Statement for Offering of
                531,611 Shares of Common Stock

Dear Ladies and Gentlemen:

        We have acted as counsel to Cisco Systems, Inc., a California
corporation (the "Company"), in connection with the registration on Form S-8
(the "Registration Statement") under the Securities Act of 1933, as amended, of
531,611 shares of common stock (the "Shares") and related stock options under
the Exio Communications, Inc. 1999 Stock Option Plan (the "Plan").

        This opinion is being furnished in accordance with the requirements of
Item 8 of Form S-8 and Item 601(b)(5)(i) of Regulation S-K.

        We have reviewed the Company's charter documents and the corporate
proceedings taken by the Company in connection with the assumption of the Plan
and the outstanding options thereunder. Based on such review, we are of the
opinion that if, as and when the Shares are issued and sold (and the
consideration therefor received) pursuant to the provisions of option agreements
duly authorized under the Plan and in accordance with the Registration
Statement, such Shares will be duly authorized, legally issued, fully paid and
nonassessable.

        We consent to the filing of this opinion letter as Exhibit 5 to the
Registration Statement.

        This opinion letter is rendered as of the date first written above and
we disclaim any obligation to advise you of facts, circumstances, events or
developments which hereafter may be brought to our attention and which may
alter, affect or modify the opinion expressed herein. Our opinion is expressly
limited to the matters set forth above and we render no opinion, whether by
implication or otherwise, as to any other matters relating to the Company, the
Plan or the Shares.


                                      Very truly yours,



                                      /S/ BROBECK, PHLEGER & HARRISON LLP

