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                             SECOND AMENDMENT TO THE
                                F5 NETWORKS, INC.
                      401(k) PROFIT SHARING PLAN AND TRUST



        F5 Networks, Inc. (the "Employer"), pursuant to Article XVII of the F5
Networks, Inc. 401(k) Profit Sharing Plan and Trust (the "Plan"), does hereby
amend the Plan as follows, effective June 1, 1999:

        1. Article II is amended to add, in alphabetical order, a new definition
of "Employer Security" to read as follows and to reletter the paragraphs that
follow and all internal references thereto correspondingly:

                    I. "Employer Security" means shares of the Employer's
           Common Stock.

        2. Article VII, Paragraph A(4) is amended by adding thereto the
following additional text at the end thereof:

           A Participant entitled to receive a distribution whose account
           contains Employer Securities may elect to receive such
           securities in kind subject to the Committee's discretion to
           require by rule that the distribution be of a minimum number
           of shares.

        3. Article IX is amended by adding a new Paragraph L to read as follows:

                    L. VOTING EMPLOYER SECURITIES.  Each Participant may
           direct the Trustee with respect to the manner in which
           Employer Securities credited to his or her account shall be
           voted. Such instructions shall be provided pursuant to rules
           and procedures promulgated by the Committee. Any shares of
           Employer Securities with respect to which the Trustee receives
           no instructions shall not be voted by the Trustee, provided,
           the Committee may direct the Trustee to vote such shares if
           the Committee determines that such action is consistent with
           its fiduciary obligations under ERISA. The Committee shall
           establish procedures to assure the confidentiality of voting
           instructions received by Participants to assure that the same
           shall not be divulged or released to any person including
           officers and employees of any Employer.

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        4. Article X, Paragraph A, is amended to read as follows:

                    A. INVESTMENTS. Each Participant may elect to direct
           the investment of his accounts through one (but not a
           combination of both) of the following: (1) by establishing an
           individual brokerage account with a brokerage firm selected by
           the Committee, or (2) by choosing among the pooled investment
           funds offered under the Plan, which shall be designated by the
           Committee and are subject to change from time to time.

           To the extent a Participant exercises control over the
           investment of his account, the Trustee shall have no
           responsibility or authority to invest or reinvest, manage or
           control the assets of such account.

           Each pooled investment fund offered under the Plan shall
           consist of a diversified portfolio of securities under the
           management of an investment manager selected by the Committee
           or a registered investment company selected by the Committee.
           Participant direction with respect to the investment of his or
           her accounts shall be made in accordance with rules adopted by
           the Committee and uniformly applied. Transfer among the
           accounts or from the brokerage account to the pooled funds
           shall be permitted by the Committee pursuant to rules adopted
           by the Committee and uniformly applied. In the event a
           Participant fails to direct the investment of his account, the
           account shall be invested in such pooled fund or funds as
           shall be selected by the Trustee.

           A Participant who has established an individual brokerage
           account may acquire Employer Securities either directly from
           the Employer or in the open market. No brokerage fees or
           commissions shall be charged by the Employer. Shares of
           Employer Securities acquired from the Employer in the initial
           public offering shall be at the offering price. Any shares
           thereafter purchased from the Employer shall be at the closing
           price of the Employer Securities on the previous day as
           reported by NASDAQ. Shares purchased on the open market shall
           be at the price obtained by the broker. Dividends on Employer
           Securities credited to the Participant's account will be paid
           in cash and credited to the Participant's individual brokerage
           account.

           Subject to Paragraph C of this Article X, the Trustee is
           hereby granted full power and authority to invest to reinvest
           the principal and income of the Trust Fund in such assets as
           shall be directed by the Committee or the investment manager
           or managers. Without limiting the generality of the foregoing,
           the Trustee may invest in Employer Securities, common stocks,
           collective investment funds (the terms of which are
           incorporated herein by reference), registered investment
           company shares, real estate, government,

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           municipal or corporate bonds, debentures or notes, or any
           other form of income producing property, whether real,
           personal or mixed, including corporate stock, corporate stock
           and life insurance policies on key employees or the employer
           for the benefit of the Trust.

           The Trustee shall not be liable for any loss or for any breach
           of fiduciary responsibility which results from a Participant's
           exercise of control over all or part of the investment plan
           accounts.

         IN WITNESS WHEREOF, the Employer has caused this amendment to be
executed this 1st day of June, 1999.

                                           F5 NETWORKS, INC.


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