
<PAGE>

                                      EXHIBIT C

THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
UNDER THE SECURITIES ACT OF 1933, AND HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT
WITH A VIEW TO, OR IN CONNECTION WITH, THE SALE OR DISTRIBUTION THEREOF. NO SUCH
SALE OR DISPOSITION MAY BE EFFECTED WITHOUT AN EFFECTIVE REGISTRATION STATEMENT
RELATED THERETO OR AN OPINION OF COUNSEL FOR THE COMPANY THAT SUCH REGISTRATION
IS NOT REQUIRED UNDER THE SECURITIES ACT OF 1933 OR THE COMPANY IS OTHERWISE
SATISFIED THAT REGISTRATION IS NOT REQUIRED.
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Warrant No. CSW _______                     Number of Shares:___________
Date of Issuance:  November__, 1997              (subject to adjustment)

                                   F5 LABS, INC.

                            COMMON STOCK PURCHASE WARRANT

    F5 LABS, INC., a Washington corporation (the "Company"), for value
received, hereby certifies that ___________, or its registered assigns (the
"Registered Holder"), is entitled, subject to the terms set forth below, to
purchase from the Company, at any time after the date hereof and on or before
November __ 2002, up to _______ shares of Common Stock, at a purchase price of
$1.60 per share.  The number of shares purchasable upon exercise of this
Warrant, and the purchase price per share, each as adjusted from time to time
pursuant to the provisions of this Warrant, are hereinafter referred to as the
"Warrant Stock" and the "Purchase Price," respectively.

    1.   EXERCISE.

         (a)  This Warrant may be exercised by the Registered Holder, in whole
or in part, by surrendering this Warrant, with the purchase form appended hereto
as Exhibit A duly executed by such Registered Holder or by such Registered
Holder's duly authorized attorney, at the principal office of the Company, or at
such other office or agency as the Company may designate, accompanied by payment
in full by cash, check or wire transfer of the Purchase Price payable in respect
of the number of shares of Warrant Stock purchased upon such exercise.

         (b)  Each exercise of this Warrant shall be deemed to have been
effected immediately prior to the close of business on the day on which this
Warrant shall have been surrendered to the Company as provided in Section 1(a)
above. At such time, the person or persons in whose name or names any
certificates for Warrant Stock shall be issuable upon such exercise as provided
in Section 1(d) below shall be deemed to have become the holder or holders of
record of the Warrant Stock represented by such certificates.

         (c)  NET ISSUE EXERCISE.

              (i)  In lieu of exercising this Warrant in the manner provided
above in Section 1(a), the Registered Holder may elect to receive shares equal
to the value of this Warrant (or the portion thereof being canceled) by
surrender of this Warrant at the principal office of the Company together with
notice of such election in which event the Company shall issue to holder a
number of shares of Common Stock computed using the following formula:


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                   X =   Y (A - B)
                         ---------
                             A
Where    X = The number of shares of Common Stock to be issued to the
                Registered Holder.

         Y = The number of shares of Common Stock purchasable under this
                Warrant (at the date of such calculation).

         A = The fair market value of one share of Common Stock (at the date
                of such calculation).

         B = The Purchase Price (as adjusted to the date of such calculation).

              (ii) For purposes of this Section 1(c), the fair market value of
Common Stock shall be the price per share which the Company could obtain from a
willing buyer for the shares sold by the Company from authorized but unissued
shares, as such price shall determined in good faith by the Board of Directors
of the Company. In the event this warrant is issued in conjunction with the
Company's initial public offering, fair market value shall be the price to the
public in such offering, prior to commissions and discounts to the
underwriters.

         (d) As soon as practicable after the exercise of this Warrant in full
or in part, and in any event within 10 days thereafter, the Company at its
expense will cause to be issued in the name of, and delivered to, the Registered
Holder, or as such Holder (upon payment by such Holder of any applicable
transfer taxes) may direct:

              (i)  a certificate or certificates for the number of shares of
Warrant Stock to which such Registered Holder shall be entitled, and

              (ii) in case such exercise is in part only, a new warrant or
warrants (dated the date hereof) of like tenor, calling in the aggregate on the
face or faces thereof for the number of shares of Warrant Stock equal (without
giving effect to any adjustment therein) to the number of such shares called for
on the face of this Warrant minus the number of such shares purchased by the
Registered Holder upon such exercise as provided in Section 1(a) above.

    2.   ADJUSTMENTS.

         (a)  If outstanding shares of the Company's Common Stock shall be
subdivided into a greater number of shares or a dividend in Common Stock shall
be paid in respect of Common Stock, the Purchase Price in effect immediately
prior to such subdivision or at the record date of such dividend shall
simultaneously with the effectiveness of such subdivision or immediately after
the record date of such dividend be proportionately reduced. If outstanding
shares of Common Stock shall be combined into a smaller number of shares, the
Purchase Price in effect immediately prior to such combination shall,
simultaneously with the effectiveness of such combination, be proportionately
increased. When any adjustment is required to be made in the Purchase Price, the
number of shares of Warrant Stock purchasable upon the exercise of this Warrant
shall be changed to the number determined by dividing (i) an amount equal to the
number of shares issuable upon the exercise of this Warrant immediately prior to
such adjustment, multiplied by the Purchase Price in effect immediately prior to
such adjustment, by (ii) the Purchase Price in effect immediately after such
adjustment.

         (b)  In case of any reclassification or change of the outstanding
securities of the Company or of any reorganization of the Company (or any other
corporation the stock or securities of


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which are at the time receivable upon the exercise of this Warrant) or any
similar corporate reorganization on or after the date hereof, then and in each
such case the holder of this Warrant, upon the exercise hereof at any time after
the consummation of such reclassification, change, reorganization, merger or
conveyance, shall be entitled to receive, in lieu of the stock or other
securities and property receivable upon the exercise hereof prior to such
consummation, the stock or other securities or property to which such holder
would have been entitled upon such consummation if such holder had exercised
this Warrant immediately prior thereto, all subject to further adjustment as
provided in paragraph (a); and in each such case, the terms of this Section 2
shall be applicable to the shares of stock or other securities properly
receivable upon the exercise of this Warrant after such consummation.

         (c)  When any adjustment is required to be made in the Purchase Price,
the Company shall promptly mail to the Registered Holder a certificate setting
forth the Purchase Price after such adjustment and setting forth a brief
statement of the facts requiring such adjustment. Such certificate shall also
set forth the kind and amount of stock or other securities or property into
which this Warrant shall be exercisable following the occurrence of any of the
events specified in Section 2(a) or (b) above.

    3.   TRANSFERS.

         (a)  Each holder of this Warrant acknowledges that this Warrant and
the Warrant Stock have not been registered under the Securities Act of 1933, as
amended (the "Securities Act"), and agrees not to sell, pledge, distribute,
offer for sale, transfer or otherwise dispose of this Warrant or any Warrant
Stock in the absence of (i) an effective registration statement under the Act as
to this Warrant or such Warrant Stock and registration or qualification of this
Warrant or such Warrant Stock under any applicable Blue Sky or state securities
law then in effect, (ii) an opinion of counsel, satisfactory to the Company,
that such registration and qualification are not required, or (iii) the Company
is otherwise satisfied that registration is not required,

         Each certificate or other instrument for Warrant Stock issued upon the
exercise of this Warrant shall bear a legend substantially to the foregoing
effect.

         (b)  Subject to the provisions of Section 3(a) hereof, this Warrant
and all rights hereunder are transferable, in whole or in part, upon surrender
of the Warrant with a properly executed assignment (in the form of Exhibit B
hereto) at the principal office of the Company PROVIDED, HOWEVER, that this
Warrant may not be transferred in part unless the transferee acquires the right
to purchase at least 25,000 shares (as adjusted pursuant to Section 2)
hereunder.

         (c)  Until any transfer of this Warrant is made in the warrant
register, the Company may treat the Registered Holder of this Warrant as the
absolute owner hereof for all purposes; PROVIDED, HOWEVER, that if and when this
warrant is properly assigned in blank, the Company may (but shall not be
required to) treat the bearer hereof as the absolute owner hereof for all
purposes, notwithstanding any notice to the contrary.

         (d)  The Company will maintain a register containing the names and
addresses of the Registered Holders of this Warrant. Any Registered Holder may
change such Registered Holder's address as shown on the warrant register by
written notice to the Company requesting such change. 

    4.   NO IMPAIRMENT. The Company will not, by amendment of its charter or 
through reorganization, consolidation, merger, dissolution, sale of assets or 
any other voluntary action, avoid or seek to avoid the observance or 
performance of any of the terms of this Warrant, but will (subject to Section 
14 below) at all times in good faith assist in the carrying out of all such 
terms and in the taking of

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<PAGE>

all such action as may be necessary or appropriate in order to protect the
rights of the holder of this Warrant against impairment. 

    5.   Termination. This Warrant (and the right to purchase securities upon
exercise hereof) shall terminate on November ____, 2002.

    6.   NOTICES OF CERTAIN TRANSACTIONS. In case:

         (a)  the Company shall take a record of the holders of its Common
Stock (or other stock or securities at the time deliverable upon the exercise of
this Warrant) for the purpose of entitling or enabling them to receive any
dividend or other distribution, or to receive any right to subscribe for or
purchase any shares of stock of any class or any other securities, or to receive
any other right, to subscribe for or purchase any shares of stock of any class
or any other securities, or to receive any other right, or

         (b)  of any capital reorganization of the Company, any
reclassification of the capital stock of the Company, any consolidation or
merger of the Company, any consolidation or merger of the Company with or into
another corporation (other than a consolidation or merger in which the Company
is the surviving entity), or any transfer of all or substantially all of the
assets of the Company, or

         (c)  of the voluntary or involuntary dissolution, liquidation or
winding-up of the Company, or

         (d)  of any redemption of the Common Stock, or

         (e) the Company pays a dividend or makes a distribution on the Common
Stock payable otherwise than in cash out of earnings or earned surplus
(determined in accordance with generally accepted accounting principles) except
for a stock dividend payable in shares of Common Stock,

then, and in each such case, the Company will mail or cause to be mailed to the
Registered Holder of this Warrant a notice specifying, as the case may be, (i)
the date on which a record is to be taken for the purpose of such dividend,
distribution or right, and stating the amount and character of such dividend,
distribution or right, or (ii) the effective date on which such reorganization,
reclassification, consolidation, merger, transfer, dissolution, liquidation,
winding-up or redemption is to take place, and the time, if any is to be fixed,
as of which the holders of record of Common Stock (or such other stock or
securities at the time deliverable upon such reorganization, reclassification,
consolidation, merger, transfer, dissolution, liquidation, winding-up or
redemption) are to be determined. Such notice shall be mailed at least ten (10)
days prior to the record date or effective date for the event specified in such
notice.

    7.   RESERVATION OF STOCK. The Company will at all times reserve and keep
available, solely for the issuance and delivery upon the exercise of this
Warrant, such shares of Warrant Stock and other stock, securities and property,
as from time to time shall be issuable upon the exercise of this Warrant.

    8.   EXCHANGE OF WARRANTS. Upon the surrender by the Registered Holder of
any Warrant or Warrants, properly endorsed, to the Company at the principal
office of the Company, the Company will, subject to the provisions of Section 3
hereof, issue and deliver to or upon the order of such Holder, at the Company's
expense, a new Warrant or Warrants of like tenor, in the name of such Registered
Holder or as such Registered Holder (upon payment by such Registered Holder of
any applicable transfer taxes)


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may direct, calling in the aggregate on the face or faces thereof for the number
of shares of Common Stock called for on the face or faces of the Warrant or
Warrants so surrendered.

    9.   REPLACEMENT OF WARRANTS. Upon receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and (in the case of loss, theft or destruction) upon delivery of an
indemnity agreement (with surety if reasonably required) in an amount reasonably
satisfactory to the Company, or (in the case of mutilation) upon surrender and
cancellation of this Warrant, the Company will issue, in lieu thereof, a new
Warrant of like tenor.

    10.  NOTICES. Unless otherwise provided, any notice required or permitted
under this Warrant shall be given in writing and shall be deemed effective (i)
upon personal delivery to the party to be notified, (ii) by facsimile
transmission (receipt confirmed) or (iii) otherwise delivered by hand or prepaid
air express courier with regular service to the addressee, addressed to the
party to be notified at the address of the Registered Holder on the records of
or most recently furnished in writing to the Company, or in the case of the
Company at 200 1st Avenue West, Suite 500, Seattle, Washington 98119, or at such
other address as such party may designate by ten days' advance written notice to
the other parties. Any notice required hereunder to be given to Brittania
Holdings Limited shall also be copied to Chi-Dooh Li, Esq., Ellis Li &
McKinstry, 999 Third Avenue, Suite 3700, Seattle, Washington 98104-4006. Any
notice required hereunder to be given to the Company shall also be copied to
William A. Carleton, Esq., Cairncross & Hempelmann, P.S., 701 Fifth Avenue,
Suite 7000, Seattle, Washington 98104-7016.

    11.  NO RIGHTS AS SHAREHOLDER. Until the exercise of this Warrant, the
Registered Holder of this Warrant shall not have or exercise any rights by
virtue hereof as a shareholder of the Company.

    12.  NO FRACTIONAL SHARES. No fractional shares of Common Stock will be
issued in connection with any exercise hereunder. In lieu of any fractional
shares which would otherwise be issuable, the Company shall round the number of
shares of Common Stock to be issued to the nearest whole number of shares.

    13.  MERGER, CONSOLIDATION OR OTHER REORGANIZATION. In case of any merger,
consolidation or other reorganization of the Company into or with any other
corporation or other business entity, then each underlying share of Common Stock
originally purchasable by exercise of this Warrant immediately prior to such
merger, consolidation or other reorganization shall upon exercise of this
Warrant be replaced for the purposes hereof by the stock or other securities
issuable or distributable in respect of each share of stock of the Company upon
such merger, consolidation or other reorganization.

    14.  AMENDMENT OR WAIVER. Any term of this Warrant may be amended or waived
only by an instrument in writing signed by the party against which enforcement
of the amendment or waiver is sought.

    15.  HEADINGS. The headings in this Warrant are for purposes of reference
only and shall not limit or otherwise affect the meaning of any provision of
this Warrant.


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    16.  GOVERNING LAW. This Warrant shall be governed, construed and
interpreted in accordance with the laws of the State of Washington, without
giving effect to principles of conflicts of law.

                                  F5 LABS, INC.


                                  By
                                    -----------------------------------
                                  Jeffrey S. Hussey
                                  President and Chief Executive 0fficer

                                  Address:  ______________________
                                            ______________________



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