Exhibit 31.1

CERTIFICATIONS

     I, John McAdam, certify that:

1) I have reviewed this Quarterly Report on Form 10-Q of F5 Networks, Inc.;

2) Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.

Date: May 13, 2010

/s/ JOHN MCADAM John McAdam

Chief Executive Officer and President