January 19, 2007

Mr. Mark Kronforst
Accounting Branch Chief
Securities and Exchange Commission
Division of Corporation Finance
100 F Street N.E.
Washington, DC 20549

Re:  F5 Networks, Inc.
Form 10-K/A for the fiscal year ended September 30, 2005
Filed December 12, 2006
File No. 000-26041

Dear Mr. Kronforst,

This letter will confirm my discussion today with Christine Davis of your office regarding F5 Networks, Inc.’s response to the comments of the Staff of the Division of Corporation Finance set forth in your letter dated January 8, 2007. We expect to submit this response on or before Friday, January 26, 2007 and appreciate your accommodation of our request.

At the direction of Ms. Davis, this letter is being filed on EDGAR under submission type: CORRESP.

Please contact me if you have any questions regarding this matter. My direct line here at F5 Networks, Inc. is 206-272-6462, email j.christianson@f5.com.

Sincerely,

/s/Jeffrey A. Christianson

Jeffrey A. Christianson
Sr. Vice President and General Counsel

cc:  Christine Davis, Staff Accountant — Via Facsimile 202-772-9210