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                                F5 NETWORKS, INC.

                 1999 NON-EMPLOYEE DIRECTORS' STOCK OPTION PLAN

                 ADOPTED BY THE BOARD OF DIRECTORS APRIL 5, 1999
                APPROVED BY STOCKHOLDERS _______________, 199___

                          EFFECTIVE DATE: APRIL 5, 1999
                         TERMINATION DATE: APRIL 4, 2009

1.   PURPOSES.

     (a)  ELIGIBLE OPTION RECIPIENTS. The persons eligible to receive
Options are the  Non-Employee  Directors of the Company.

     (b)  AVAILABLE OPTIONS. The purpose of the Plan is to provide a means by
which Non-Employee Directors may be given an opportunity to benefit from
increases in value of the Common Stock through the granting of Nonstatutory
Stock Options.

     (c)  GENERAL PURPOSE. The Company, by means of the Plan, seeks to retain
the services of its Non-Employee Directors, to secure and retain the services
of new Non-Employee Directors and to provide incentives for such persons to
exert maximum efforts for the success of the Company and its Affiliates.

2.   DEFINITIONS.

     (a)  "AFFILIATE" means any parent corporation or subsidiary corporation
of the Company, whether now or hereafter existing, as those terms are defined
in Sections 424(e) and (f), respectively, of the Code.

     (b)  "ANNUAL GRANT" means an Option granted annually to all Non-Employee
Directors who meet the specified criteria pursuant to subsection 6(b) of the
Plan.

     (c)  "ANNUAL MEETING" means the annual meeting of the stockholders of the
Company.

     (d)  "BOARD" means the Board of Directors of the Company.

     (e)  "CODE" means the Internal Revenue Code of 1986, as amended.

     (f)  "COMMON STOCK" means the common stock of the Company.

     (g)  "COMPANY" means F5 Networks, Inc., a Washington corporation.

     (h)  "CONSULTANT" means any person, including an advisor, (i) engaged by
the Company or an Affiliate to render consulting or advisory services and who
is compensated for such services or (ii) who is a member of the Board of
Directors of an Affiliate. However, the

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term "Consultant" shall not include either Directors of the Company who are
not compensated by the Company for their services as Directors or Directors of
the Company who are merely paid a director's fee by the Company for their
services as Directors.

     (i)  "CONTINUOUS SERVICE" means that the Optionholder's service with the
Company or an Affiliate, whether as an Employee, Director or Consultant, is
not interrupted or terminated. The Optionholder's Continuous Service shall not
be deemed to have terminated merely because of a change in the capacity in
which the Optionholder renders service to the Company or an Affiliate as an
Employee, Consultant or Director or a change in the entity for which the
Optionholder renders such service, provided that there is no interruption or
termination of the Optionholder's Continuous Service. For example, a change in
status from a Non-Employee Director of the Company to a Consultant of an
Affiliate or an Employee of the Company will not constitute an interruption of
Continuous Service. The Board or the chief executive officer of the Company,
in that party's sole discretion, may determine whether Continuous Service
shall be considered interrupted in the case of any leave of absence approved
by that party, including sick leave, military leave or any other personal
leave.

     (j)  "DIRECTOR" means a member of the Board of Directors of the Company.

     (k)  "DISABILITY" means the inability of a person, in the opinion of a
qualified physician acceptable to the Company, to perform the major duties of
that person's position with the Company or an Affiliate of the Company because
of the sickness or injury of the person.

     (l)  "EMPLOYEE" means any person employed by the Company or an Affiliate.
Mere service as a Director or payment of a director's fee by the Company or an
Affiliate shall not be sufficient to constitute "employment" by the Company or
an Affiliate.

     (m)  "EXCHANGE ACT" means the Securities Exchange Act of 1934, as amended.

     (n)  "FAIR MARKET VALUE" means, as of any date, the value of the Common
Stock determined as follows:

          (i)  If the Common Stock is listed on any established stock exchange
or traded on the Nasdaq National Market or the Nasdaq SmallCap Market, the
Fair Market Value of a share of Common Stock shall be the closing sales price
for such stock (or the closing bid, if no sales were reported) as quoted on
such exchange or market (or the exchange or market with the greatest volume of
trading in the Common Stock) on the last market trading day prior to the day
of determination, as reported in The Wall Street Journal or such other source
as the Board deems reliable.

          (ii) In the absence of such markets for the Common Stock, the Fair
Market Value shall be determined in good faith by the Board.

     (o)  "INITIAL GRANT" means an Option granted to a Non-Employee Director
who meets the specified criteria pursuant to subsection 6(a) of the Plan.

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     (p)  "IPO DATE" means the effective date of the initial public offering
of the Common Stock.

     (q)  "NON-EMPLOYEE DIRECTOR" means a Director who is not employed by the
Company or an Affiliate, and who is not elected or appointed as a Director in
direct connection with such Director's investment in the Company or with an
investment in the Company by an entity with whom such Director is affiliated
or by which such Director is designated as a representative.

     (r)  "NONSTATUTORY STOCK OPTION" means an Option not intended to qualify
as an incentive stock option within the meaning of Section 422 of the Code and
the regulations promulgated thereunder.

     (s)  "OFFICER" means a person who is an officer of the Company within the
meaning of Section 16 of the Exchange Act and the rules and regulations
promulgated thereunder.

     (t)  "OPTION" means a Nonstatutory Stock Option granted pursuant to the
Plan.

     (u)  "OPTION AGREEMENT" means a written agreement between the Company and
an Optionholder evidencing the terms and conditions of an individual Option
grant. Each Option Agreement shall be subject to the terms and conditions of
the Plan.

     (v)  "OPTIONHOLDER" means a person to whom an Option is granted pursuant
to the Plan or, if applicable, such other person who holds an outstanding
Option.

     (w)  "PLAN" means this F5 Networks, Inc. 1999 Non-Employee Directors' 
Stock Option Plan.

     (x)  "RULE 16b-3" means Rule 16b-3 promulgated under the Exchange Act or
any successor to Rule 16b-3, as in effect from time to time.

     (y)  "SECURITIES ACT" means the Securities Act of 1933, as amended.

3.   ADMINISTRATION.

     (a)  ADMINISTRATION BY BOARD. The Board shall administer the Plan. The
Board may not delegate administration of the Plan to a committee.

     (b)  POWERS OF BOARD. The Board shall have the power, subject to, and
within the limitations of, the express provisions of the Plan:

          (i)   To determine the provisions of each Option to the extent not
specified in the Plan.

          (ii)  To construe and interpret the Plan and Options granted
under it, and to establish, amend and revoke rules and regulations for its
administration. The Board, in the exercise of this power, may correct any
defect, omission or inconsistency in the Plan or in any

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Option Agreement, in a manner and to the extent it shall deem necessary or
expedient to make the Plan fully effective.

          (iii) To amend the Plan or an Option as provided in Section 12.

          (iv)  Generally, to exercise such powers and to perform such
acts as the Board deems necessary or expedient to promote the best interests
of the Company which are not in conflict with the provisions of the Plan.

4.   SHARES SUBJECT TO THE PLAN.

     (a)  SHARE RESERVE. Subject to the provisions of Section 11 relating to
adjustments upon changes in stock, the stock that may be issued pursuant to
Options shall not exceed in the aggregate one hundred thousand (100,000)
shares of Common Stock.

     (b)  REVERSION OF SHARES TO THE SHARE RESERVE. If any Option shall for
any reason expire or otherwise terminate, in whole or in part, without having
been exercised in full, the stock not acquired under such Option shall revert
to and again become available for issuance under the Plan.

     (c)  SOURCE OF SHARES. The stock subject to the Plan may be unissued
shares or reacquired shares, bought on the market or otherwise.

5.   ELIGIBILITY.

     Nondiscretionary Options as set forth in section 6 shall be granted under
the Plan to all Non-Employee Directors.

6.   NON-DISCRETIONARY GRANTS.

     (a)  INITIAL GRANTS. Without any further action of the Board, each
Non-Employee Director shall be granted the following Options:

          (i)  After the IPO Date, each person who is elected or appointed for
the first time to be a Non-Employee Director automatically shall, upon the
date of his or her initial election or appointment to be a Non-Employee
Director by the Board or stockholders of the Company, be granted an Initial
Grant to purchase five thousand (5,000) shares of Common Stock on the terms
and conditions set forth herein.

     (b)  ANNUAL GRANTS. On the day following each Annual Meeting commencing
with the Annual Meeting in 2000, each person who is then a Non-Employee
Director and has been a Non-Employee Director for at least six (6) months
automatically shall be granted an Annual Grant to purchase five thousand
(5,000) shares of Common Stock on the terms and conditions set forth herein.

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7.   OPTION PROVISIONS.

     Each Option shall be in such form and shall contain such terms and
conditions as required by the Plan. Each Option shall contain such additional
terms and conditions, not inconsistent with the Plan, as the Board shall deem
appropriate. Each Option shall include (through incorporation of provisions
hereof by reference in the Option or otherwise) the substance of each of the
following provisions:

     (a)  TERM.  No Option shall be exercisable after the expiration of
ten (10) years from the date it was granted.

     (b)  EXERCISE PRICE. The exercise price of each Option shall be one
hundred percent (100%) of the Fair Market Value of the stock subject to the
Option on the date the Option is granted. Notwithstanding the foregoing, an
Option may be granted with an exercise price lower than that set forth in the
preceding sentence if such Option is granted pursuant to an assumption or
substitution for another option in a manner satisfying the provisions of
Section 424(a) of the Code.

     (c)  CONSIDERATION. The purchase price of stock acquired pursuant to an
Option may be paid, to the extent permitted by applicable statutes and
regulations, in any combination of (i) cash or check, (ii) delivery to the
Company of other Common Stock, (ii) deferred payment or (iv) any other form of
legal consideration that may be acceptable to the Board and provided in the
Option Agreement.

      In the case of any deferred payment arrangement, interest shall be
compounded at least annually and shall be charged at the minimum rate of
interest necessary to avoid the treatment as interest, under any applicable
provisions of the Code, of any amounts other than amounts stated to be
interest under the deferred payment arrangement.

     (d)  TRANSFERABILITY. An Option shall not be transferable except by will
or by the laws of descent and distribution and shall be exercisable during the
lifetime of the Optionholder only by the Optionholder. Notwithstanding the
foregoing, the Optionholder may, by delivering written notice to the Company,
in a form satisfactory to the Company, designate a third party who, in the
event of the death of the Optionholder, shall thereafter be entitled to
exercise the Option.

     (e)  VESTING. Options shall be fully vested and exercisable upon receipt.

     (f)  TERMINATION OF CONTINUOUS SERVICE. In the event an Optionholder's
Continuous Service terminates (other than upon the Optionholder's death or
Disability), the Optionholder may exercise his or her Option but only within
such period of time ending on the earlier of (i) the date three (3) months
following the termination of the Optionholder's Continuous Service, or (ii)
the expiration of the term of the Option as set forth in the Option Agreement.
If, after termination, the Optionholder does not exercise his or her Option
within the time specified in the Option Agreement, the Option shall terminate.

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     (g)  EXTENSION OF TERMINATION DATE. If the exercise of the Option
following the termination of the Optionholder's Continuous Service (other than
upon the Optionholder's death or Disability) would be prohibited at any time
solely because the issuance of shares would violate the registration
requirements under the Securities Act, then the Option shall terminate on the
earlier of (i) the expiration of the term of the Option set forth in
subsection 7(a) or (ii) the expiration of a period of three (3) months after
the termination of the Optionholder's Continuous Service during which the
exercise of the Option would not be in violation of such registration
requirements.

     (h)  DISABILITY OF OPTIONHOLDER. In the event an Optionholder's
Continuous Service terminates as a result of the Optionholder's Disability,
the Optionholder may exercise his or her Option (to the extent that the
Optionholder was entitled to exercise it as of the date of termination), but
only within such period of time ending on the earlier of (i) the date twelve
(12) months following such termination or (ii) the expiration of the term of
the Option as set forth in the Option Agreement. If, after termination, the
Optionholder does not exercise his or her Option within the time specified
herein, the Option shall terminate.

     (i)  DEATH OF OPTIONHOLDER. In the event (i) an Optionholder's Continuous
Service terminates as a result of the Optionholder's death or (ii) the
Optionholder dies within the three-month period after the termination of the
Optionholder's Continuous Service for a reason other than death, then the
Option may be exercised by the Optionholder's estate, by a person who acquired
the right to exercise the Option by bequest or inheritance or by a person
designated to exercise the Option upon the Optionholder's death, but only
within the period ending on the earlier of (1) the date eighteen (18) months
following the date of death or (2) the expiration of the term of such Option
as set forth in the Option Agreement. If, after death, the Option is not
exercised within the time specified herein, the Option shall terminate.

8.   COVENANTS OF THE COMPANY.

     (a)  AVAILABILITY OF SHARES. During the terms of the Options, the Company
shall keep available at all times the number of shares of Common Stock
required to satisfy such Options.

     (b)  SECURITIES LAW COMPLIANCE. The Company shall seek to obtain from
each regulatory commission or agency having jurisdiction over the Plan such
authority as may be required to grant Options and to issue and sell shares of
Common Stock upon exercise of the Options; provided, however, that this
undertaking shall not require the Company to register under the Securities Act
the Plan, any Option or any stock issued or issuable pursuant to any such
Option. If, after reasonable efforts, the Company is unable to obtain from any
such regulatory commission or agency the authority which counsel for the
Company deems necessary for the lawful issuance and sale of stock under the
Plan, the Company shall be relieved from any liability for failure to issue
and sell stock upon exercise of such Options unless and until such authority
is obtained.

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9.   USE OF PROCEEDS FROM STOCK.

     Proceeds from the sale of stock pursuant to Options shall constitute
general funds of the Company.

10.  MISCELLANEOUS.

     (a)  STOCKHOLDER RIGHTS. No Optionholder shall be deemed to be the holder
of, or to have any of the rights of a holder with respect to, any shares
subject to such Option unless and until such Optionholder has satisfied all
requirements for exercise of the Option pursuant to its terms.

     (b)  NO SERVICE RIGHTS. Nothing in the Plan or any instrument executed or
Option granted pursuant thereto shall confer upon any Optionholder any right
to continue to serve the Company as a Non-Employee Director or shall affect
the right of the Company or an Affiliate to terminate (i) the employment of an
Employee with or without notice and with or without cause, (ii) the service of
a Consultant pursuant to the terms of such Consultant's agreement with the
Company or an Affiliate or (iii) the service of a Director pursuant to the
Bylaws of the Company or an Affiliate, and any applicable provisions of the
corporate law of the state in which the Company or the Affiliate is
incorporated, as the case may be.

     (c)  INVESTMENT ASSURANCES. The Company may require an Optionholder, as a
condition of exercising or acquiring stock under any Option, (i) to give
written assurances satisfactory to the Company as to the Optionholder's
knowledge and experience in financial and business matters and/or to employ a
purchaser representative reasonably satisfactory to the Company who is
knowledgeable and experienced in financial and business matters and that he or
she is capable of evaluating, alone or together with the purchaser
representative, the merits and risks of exercising the Option; and (ii) to
give written assurances satisfactory to the Company stating that the
Optionholder is acquiring the stock subject to the Option for the
Optionholder's own account and not with any present intention of selling or
otherwise distributing the stock. The foregoing requirements, and any
assurances given pursuant to such requirements, shall be inoperative if (iii)
the issuance of the shares upon the exercise or acquisition of stock under the
Option has been registered under a then currently effective registration
statement under the Securities Act or (iv) as to any particular requirement, a
determination is made by counsel for the Company that such requirement need
not be met in the circumstances under the then applicable securities laws. The
Company may, upon advice of counsel to the Company, place legends on stock
certificates issued under the Plan as such counsel deems necessary or
appropriate in order to comply with applicable securities laws, including, but
not limited to, legends restricting the transfer of the stock.

     (d)  WITHHOLDING OBLIGATIONS. The Optionholder may satisfy any federal,
state or local tax withholding obligation relating to the exercise or
acquisition of stock under an Option by any of the following means (in
addition to the Company's right to withhold from any compensation paid to the
Optionholder by the Company) or by a combination of such means: (i) tendering
a cash payment; (ii) authorizing the Company to withhold shares from the
shares of the Common Stock otherwise issuable to the Optionholder as a result
of the exercise or acquisition

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of stock under the Option; or (iii) delivering to the Company owned and
unencumbered shares of the Common Stock.

11.  ADJUSTMENTS UPON CHANGES IN STOCK.

     (a)  CAPITALIZATION ADJUSTMENTS. If any change is made in the stock
subject to the Plan, or subject to any Option, without the receipt of
consideration by the Company (through merger, consolidation, reorganization,
recapitalization, reincorporation, stock dividend, dividend in property other
than cash, stock split, liquidating dividend, combination of shares, exchange
of shares, change in corporate structure or other transaction not involving
the receipt of consideration by the Company), the Plan will be appropriately
adjusted in the class(es) and maximum number of securities subject both to the
Plan pursuant to subsection 4(a) and to the nondiscretionary Options specified
in Section 5, and the outstanding Options will be appropriately adjusted in
the class(es) and number of securities and price per share of stock subject to
such outstanding Options. The Board shall make such adjustments, and its
determination shall be final, binding and conclusive. (The conversion of any
convertible securities of the Company shall not be treated as a transaction
"without receipt of consideration" by the Company.)

     (b)  CHANGE IN CONTROL--DISSOLUTION OR LIQUIDATION. In the event of a
dissolution or liquidation of the Company, then all outstanding Options shall
terminate immediately prior to such event.

     (c)  CHANGE IN CONTROL--ASSET SALE, MERGER, CONSOLIDATION OR REVERSE
MERGER.

          (i)  In the event of (i) a sale of all or substantially all of the
assets of the Company, (ii) a merger or consolidation in which the Company is
not the surviving corporation or (iii) a reverse merger in which the Company
is the surviving corporation but the shares of Common Stock outstanding
immediately preceding the merger are converted by virtue of the merger into
other property, whether in the form of securities, cash or otherwise, then any
surviving corporation or acquiring corporation shall assume any Options
outstanding under the Plan or shall substitute similar Options (including an
option to acquire the same consideration paid to the stockholders in the
transaction described in this subsection 11(c) for those outstanding under the
Plan.

          (ii) For purposes of subsection 11(c) an Option shall be deemed
assumed if, following the change in control, the Option confers the right to
purchase in accordance with its terms and conditions, for each share of Common
Stock subject to the Option immediately prior to the change in control, the
consideration (whether stock, cash or other securities or property) to which a
holder of a share of Common Stock on the effective date of the change in
control was entitled.

12.  AMENDMENT OF THE PLAN AND OPTIONS.

     (a)  AMENDMENT OF PLAN. The Board at any time, and from time to time, may
amend the Plan. However, except as provided in Section 11 relating to
adjustments upon changes in

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stock, no amendment shall be effective unless approved by the stockholders of
the Company to the extent stockholder approval is necessary to satisfy the
requirements of Rule 16b-3 or any Nasdaq or securities exchange listing
requirements.

     (b)  STOCKHOLDER APPROVAL. The Board may, in its sole discretion, submit
any other amendment to the Plan for stockholder approval.

     (c)  NO IMPAIRMENT OF RIGHTS. Rights under any Option granted before
amendment of the Plan shall not be impaired by any amendment of the Plan
unless (i) the Company requests the consent of the Optionholder and (ii) the
Optionholder consents in writing.

     (d)  AMENDMENT OF OPTIONS. The Board at any time, and from time to time,
may amend the terms of any one or more Options; provided, however, that the
rights under any Option shall not be impaired by any such amendment unless (i)
the Company requests the consent of the Optionholder and (ii) the Optionholder
consents in writing.

13.  TERMINATION OR SUSPENSION OF THE PLAN.

     (a)  PLAN TERM. The Board may suspend or terminate the Plan at any time.
Unless sooner terminated, the Plan shall terminate on the day before the tenth
(10th) anniversary of the date the Plan is adopted by the Board or approved by
the stockholders of the Company, whichever is earlier. No Options may be
granted under the Plan while the Plan is suspended or after it is terminated.

     (b)  NO IMPAIRMENT OF RIGHTS. Suspension or termination of the Plan shall
not impair rights and obligations under any Option granted while the Plan is
in effect except with the written consent of the Optionholder.

14.  EFFECTIVE DATE OF PLAN.

     The Plan shall become effective on the IPO Date, but no Option shall be
exercised unless and until the Plan has been approved by the stockholders of the
Company, which approval shall be within twelve (12) months before or after the
date the Plan is adopted by the Board.

15.  CHOICE OF LAW.

     All questions concerning the construction, validity and interpretation of
this Plan shall be governed by the law of the State of Washington, without
regard to such state's conflict of laws rules.

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