
<PAGE>

                               STOCK PURCHASE WARRANT
                       To Purchase Shares of Common Stock of
                                   F5 LABS, INC.


     THIS CERTIFIES that, for value received, Brittania Holdings Limited (the
"Holder") is entitled, upon the terms and subject to the conditions hereinafter
set forth, to subscribe for and purchase from F5 Labs, Inc., a Washington
corporation (the "Company"), Fifty Thousand (50,000) shares (the "Shares") of
the Company's common stock (the "Common Stock").

     This Warrant is issued pursuant to that certain Promissory Note issued by
the Company to the Holder as of March 21, 1997.

1.   EXERCISE PRICE

     The per-Share purchase price under this Warrant (the "Exercise Price")
shall be the lesser of Two Dollars ($2.00), or eighty percent (80%) of the price
per share of Series B Preferred Stock hereafter issued by the Company.

2.   EXERCISE OF WARRANT

     The purchase rights represented by this Warrant are exercisable by the 
Holder, in whole or in part, at any time during a five-year period commencing 
on March 21, 1997, by the surrender of this Warrant and the Notice of 
Exercise form annexed hereto, and upon payment of the purchase price of the 
Shares thereby purchased (by cash or by check or bank draft payable to the 
order of the Company), whereupon the Holder shall be entitled to receive a 
certificate for the number of Shares so purchased.

3.   ACCEPTANCE OF WARRANT

     By accepting this Warrant and the Promissory Note referenced herein, the
Holder acknowledges that the securities represented by these instrument 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 reasonably acceptable to the Company that such registration is not
required under the Securities Act of 1933, as amended.

4.   ISSUANCE OF SHARES; NO FRACTIONAL SHARES OR SCRIP

     Certificates for shares of Common Stock purchased hereunder shall be
delivered to the Holder within a reasonable time after the date on which this
Warrant shall have been exercised in accordance with the terms hereof.  No
fractional shares or scrip representing fractional shares shall be issued upon
the exercise of this Warrant.  With respect to any fraction of a share called
for upon the exercise of this Warrant, an amount equal to such fraction
multiplied by the then-current price at which each share may be purchased
hereunder shall be paid in cash to the Holder.


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<PAGE>

5.   CHARGES, TAXES AND EXPENSES

     Issuance of certificates for shares of Common Stock upon the exercise of
this Warrant shall be made without charge to the Holder for any issue or
transfer tax or other incidental expense in respect of the issuance of such
certificate, all of which taxes and expenses shall be paid by the Company, and
such certificates shall be issued in the name of the Holder or in such name or
names as may be directed by the Holder.

6.   NO RIGHTS AS SHAREHOLDERS

     This Warrant does not entitle the Holder to any voting rights or other
rights as a shareholder of the Company prior to the exercise thereof.

7.   REGISTRY OF WARRANT

     The Company shall maintain at the above-mentioned office or agency a
registry showing the name and address of the Holder of this Warrant.  This
Warrant may be surrendered for exchange, transfer or exercise, in accordance
with its terms, at such office or agency of the Company, and the Company shall
be entitled to rely in all respects, prior to written notice to the contrary,
upon such registry.

8.   LOSS, THEFT, DESTRUCTION OR MUTILATION OF WARRANT

     Upon receipt by the Company of evidence reasonably satisfactory to it of
the loss, theft, destruction or mutilation of this Warrant, and in case of loss,
theft or destruction, of indemnity or security reasonably satisfactory to it,
and upon reimbursement to the Company of all reasonable expenses incidental
thereto, and upon surrender and cancellation of this Warrant, if mutilated, the
Company will make and deliver a new Warrant of like tenor and dated as of such
cancellation, in lieu of this Warrant.

9.   SATURDAYS, SUNDAYS, HOLIDAYS, ETC.

     If the last or appointed day for the taking of any action or the expiration
of any right required or granted herein shall be a Saturday or a Sunday or shall
be a legal holiday, then such action may be taken or such right may be exercised
on the next succeeding day not a legal holiday.

10.  EARLY TERMINATION; RECLASSIFICATION

     (a)  MERGER, SALE OF ASSETS.  If at any time the Company proposes to merge
with or into any other corporation, effect a reorganization or sell or convey
all or substantially all of its assets to any other entity in a transaction in
which the shareholders of the Company immediately before the transaction own
immediately after the transaction less than a majority of the outstanding voting
securities of the surviving entity (or its parent), then:  (i) the Company shall
give the Holder thirty (30) days notice of the proposed effective date of such
transaction; and (ii) if the Warrant has not been exercised by the effective
date of such transaction it shall terminate.


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<PAGE>

     (b)  RECLASSIFICATION, ETC.  If the Company at any time shall, by
subdivision, combination or reclassification of securities or otherwise, change
any of the securities to which purchase rights under this Warrant exist into the
same or a different number of securities of any other class or classes, this
Warrant shall thereafter be to acquire such number and kind of securities as
would have been issuable as the result of such change with respect to the
securities which were subject to the purchase rights under this Warrant
immediately prior to such subdivision, combination, reclassification or other
change.

     (c)  AUTHORIZED SHARES.  The Company covenants that during the period the
Warrant is outstanding, it will reserve from its authorized and unissued Common
Stock a sufficient number of shares to provide for the issuance of shares of
Common Stock upon the exercise of any purchase rights under this Warrant.

11.  MISCELLANEOUS

     This Warrant shall be binding upon any successors or assigns of the
Company.  This Warrant shall constitute a contract under the laws of the State
of Washington and for all purposes shall be construed in accordance with and
governed by the laws of said state.

     IN WITNESS WHEREOF, the Company has caused this Warrant to be executed as
of March 15, 1997.

                                             F5 LABS, INC.



                                             By /s/ Jeffrey S. Hussey
                                                --------------------------------
                                                Jeffrey S. Hussey, President

ACCEPTED:

BRITANNIA HOLDINGS LIMITED



By
   --------------------------------


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                                  NOTICE OF EXERCISE


TO:  F5 LABS, INC.

     (1)  The undersigned hereby elects to purchase ____ shares of Common Stock
of F5 Labs, Inc. pursuant to the terms of the attached Warrant, and tenders
herewith payment of the purchase price in full, together with all applicable
transfer taxes, if any.

     (2)  Please issue a certificate or certificates representing said shares of
Common Stock in the name of the undersigned or in such other name as is
specified below.



                              -------------------------
                                        (Name)



                              -------------------------
                                      (Address)



     (3)  The undersigned represents that the aforesaid shares of Common Stock
are being acquired for the account of the undersigned for investment and not
with a view to, or for resale in connection with, the distribution thereof and
that the undersigned has no present intention of distributing or reselling such
shares.



-------------------------               -----------------------------------
        (Date)                                      (Signature)


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