Exhibit 99.1

FOR IMMEDIATE RELEASE

CONTACT:		Investor Relations
		John Eldridge
		(206) 272-6571
		j.eldridge@f5.com
		Public Relations
		Alane Moran
		(206) 272-6850
		a.moran@f5.com

F5 Networks Announces Results for Third Quarter of Fiscal 2011

SEATTLE, WA—July 20, 2011— For the third quarter of fiscal 2011, F5 Networks, Inc. (NASDAQ: FFIV) announced revenue of $290.7 million, up 4.7 percent from $277.6 million in the prior quarter and 26.1 percent from $230.5 million in the third quarter of fiscal 2010.

GAAP net income was $62.5 million ($0.77 per diluted share), compared to $55.6 million ($0.68 per diluted share) in the prior quarter and $40.5 million ($0.50 per diluted share) in the third quarter a year ago.

Excluding the impact of stock-based compensation net of tax, non-GAAP net income was $79.4 million ($0.97 per diluted share), compared to $71.5 million ($0.88 per diluted share) in the prior quarter and $53.3 million ($0.66 per diluted share) in the third quarter of fiscal 2010.

A reconciliation of GAAP net income to non-GAAP net income is included on the attached Consolidated Statements of Operations.

“Strong sales in APAC and Japan, in particular of our high-end products, accounted for most of the revenue growth during the quarter,” said John McAdam, F5 president and chief executive officer. “EMEA revenue was down from the prior quarter, and Americas revenue was up only slightly, due in part to a slowdown in U.S. Federal sales.

“In June we began shipping VIPRION 2400, our new chassis-based application delivery controller that offers scalable performance and other advanced features of the VIPRION architecture at a price in the mid-range of our ADC product family. Both enterprise customers and service providers have expressed growing interest in this product, and we expect sales to ramp steadily over the next several quarters. This quarter, we are on track to release version 11.0 of our TMOS operating system, which includes user-friendly application templates, support for virtual clustered multi-processing, and more than 150 new features, many of them geared toward service providers.

“With the rollout of these new products and a number of others over the coming year, we continue to believe that our competitive position in the traditional ADC market has never been stronger, and that the opportunity to expand our footprint in adjacent markets has never been greater. As a result, we remain confident in our ability to sustain top-line growth and profitability by continuing to expand our reach into new and existing markets and by hiring and retaining the best people.

“During the third quarter we added 95 employees, roughly a third of them in sales and sales support. At the same time, productivity across the organization enabled us to achieve a non-GAAP operating profit margin of 38.2 percent,” McAdam said.

The company also continued to strengthen its financial position during the quarter, generating $101 million in cash from operations. After repurchasing 471,633 shares of our outstanding common stock F5 ended the quarter with $1.06 billion in cash and investments.

For the current quarter, ending September 30, management has set a revenue goal of $307 million to $312 million with a GAAP earnings target of $0.75 to $0.77 per diluted share. Excluding stock-based compensation expense, the company’s non-GAAP earnings target is $0.97 to $0.99 per diluted share.

A reconciliation of the company’s expected GAAP and non-GAAP earnings is provided in the following table:

		Three months ended
		September 30, 2011
Reconciliation of Expected Non-GAAP Fourth Quarter Earnings		Low				High
Net income		$	61.5			$	63.1
Stock-based compensation expense, net of tax		$	18.0			$	18.0
Non-GAAP net income excluding stock-based compensation expense		$	79.5			$	81.1
Net income per share — diluted		$	0.75			$	0.77
Non-GAAP net income per share — diluted		$	0.97			$	0.99

About F5 Networks

F5 Networks, Inc., the global leader in Application Delivery Networking (ADN), helps the world’s largest enterprises and service providers realize the full value of virtualization, cloud computing, and on-demand IT. F5^® solutions help integrate disparate technologies to provide greater control of the infrastructure, improve application delivery and data management, and give users seamless, secure, and accelerated access to applications from their corporate desktops and smart devices. An open architectural framework enables F5 customers to apply business policies at “strategic points of control” across the IT infrastructure and into the public cloud. F5 products give customers the agility they need to align IT with changing business

conditions, deploy scalable solutions on demand, and manage mobile access to data and services. Enterprises, service and cloud providers, and leading online companies worldwide rely on F5 to optimize their IT investments and drive business forward. For more information, go to www.f5.com.

You can also follow @f5networks on Twitter or visit us on Facebook for more information about F5, its partners, and technology. For a complete listing of F5 community sites, please visit www.f5.com/news-press-events/web-media/community.html.

Forward Looking Statements

Statements in this press release concerning the continuing strength of F5’s business, sequential growth, the target revenue and earnings range, share amount and share price assumptions, demand for application delivery networking and storage virtualization products and other statements that are not historical facts are forward-looking statements. Such forward-looking statements involve risks and uncertainties, as well as assumptions and other factors that, if they do not fully materialize or prove correct, could cause the actual results, performance or achievements of the company, or industry results, to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Such factors include, but are not limited to: customer acceptance of our new traffic management, security, application delivery, WAN optimization and storage virtualization offerings; the timely development, introduction and acceptance of additional new products and features by F5 or its competitors; competitive pricing pressures; increased sales discounts; uncertain global economic conditions which may result in reduced customer demand for our products and services and changes in customer payment patterns; F5’s ability to sustain, develop and effectively utilize distribution relationships; F5’s ability to attract, train and retain qualified product development, marketing, sales, professional services and customer support personnel; F5’s ability to expand in international markets; the unpredictability of F5’s sales cycle; the share repurchase program; future prices of F5’s common stock; and other risks and uncertainties described more fully in our documents filed with or furnished to the Securities and Exchange Commission. All forward-looking statements in this press release are based on information available as of the date hereof and qualified in their entirety by this cautionary statement. F5 assumes no obligation to revise or update these forward-looking statements.

GAAP to non-GAAP Reconciliation

F5’s management evaluates and makes operating decisions using various operating measures. These measures are generally based on the revenues of its products, services operations and certain costs of those operations, such as cost of revenues, research and development, sales and marketing and

general and administrative expenses. One such measure is net income excluding stock-based compensation, which is a non-GAAP financial measure under Section 101 of Regulation G under the Securities Exchange Act of 1934, as amended. This measure consists of GAAP net income excluding, as applicable, stock-based compensation. Net income excluding stock-based compensation (non-GAAP) is adjusted by the amount of additional taxes or tax benefit that the company would accrue if it used non-GAAP results instead of GAAP results to calculate the company’s tax liability. Stock-based compensation is a non-cash expense that F5 has accounted for since July 1, 2005 in accordance with the fair value recognition provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 718 Compensation — Stock Compensation (“FASB ASC Topic 718”).

Management believes that net income excluding stock-based compensation (non-GAAP) provides useful supplemental information to management and investors regarding the performance of the company’s business operations and facilitates comparisons to the company’s historical operating results. Although F5’s management finds this non-GAAP measure to be useful in evaluating the performance of the business, management’s reliance on this measure is limited because items excluded from such measures could have a material effect on F5’s earnings and earnings per share calculated in accordance with GAAP. Therefore, F5’s management will use its non-GAAP earnings and earnings per share measures, in conjunction with GAAP earnings and earnings per share measures, to address these limitations when evaluating the performance of the company’s business. Investors should consider these non-GAAP measures in addition to, and not as a substitute for, financial performance measures in accordance with GAAP.

F5 believes that presenting its non-GAAP measure of earnings and earnings per share provides investors with an additional tool for evaluating the performance of the company’s business and which management uses in its own evaluation of the company’s performance. Investors are encouraged to look at GAAP results as the best measure of financial performance. For example, stock-based compensation is an obligation of the company that should be considered and each line item is important to financial performance generally. However, while the GAAP results are more complete, the company provides investors this supplemental measure since, with reconciliation to GAAP, it may provide additional insight into its operational performance and financial results.

###

F5 Networks, Inc.
Condensed Consolidated Balance Sheets
(unaudited, in thousands)

		June 30,				September 30,
		2011				2010
Assets
Current assets
Cash and cash equivalents		$	299,804			$	168,754
Short-term investments			285,530				259,742
Accounts receivable, net of allowances of $2,821 and $4,319			154,741				112,132
Inventories			17,941				18,815
Deferred tax assets			9,197				8,767
Other current assets			30,015				37,745
Total current assets			797,228				605,955
Property and equipment, net			42,323				34,157
Long-term investments			471,567				433,570
Deferred tax assets			38,169				37,864
Goodwill			234,700				234,700
Other assets, net			13,147				15,946
Total assets		$	1,597,134			$	1,362,192
Liabilities and Shareholders’ Equity
Current liabilities
Accounts payable		$	34,070			$	21,180
Accrued liabilities			59,721				61,768
Deferred revenue			255,226				204,137
Total current liabilities			349,017				287,085
Other long-term liabilities			16,300				16,153
Deferred revenue, long-term			66,649				55,256
Total long-term liabilities			82,949				71,409
Commitments and contingencies
Shareholders’ equity
Preferred stock, no par value; 10,000 shares authorized, no shares outstanding			—				—
Common stock, no par value; 200,000 shares authorized 80,727 and 80,355 shares issued and outstanding			505,117				517,215
Accumulated other comprehensive loss			(3,460	)			(3,241	)
Retained earnings			663,511				489,724
Total shareholders’ equity			1,165,168				1,003,698
Total liabilities and shareholders’ equity		$	1,597,134			$	1,362,192

F5 Networks, Inc.
Condensed Consolidated Statements of Operations
(unaudited, in thousands, except per share amounts)

		Three Months Ended								Nine Months Ended
		June 30,								June 30,
		2011				2010				2011				2010
Net revenues
Products		$	179,327			$	147,393			$	524,529			$	396,170
Services			111,386				83,081				312,690				231,528
Total			290,713				230,474				837,219				627,698
Cost of net revenues (1)
Products			31,803				29,328				94,840				82,789
Services			20,645				15,251				57,244				42,335
Total			52,448				44,579				152,084				125,124
Gross Profit			238,265				185,895				685,135				502,574
Operating expenses (1)
Sales and marketing			93,633				77,219				269,790				212,505
Research and development			35,245				30,889				102,358				86,743
General and administrative			21,126				17,658				61,656				49,627
Total			150,004				125,766				433,804				348,875
Income from operations			88,261				60,129				251,331				153,699
Other income, net			1,889				3,561				6,002				7,557
Income before income taxes			90,150				63,690				257,333				161,256
Provision for income taxes (1)			27,601				23,195				83,546				58,338
Net Income		$	62,549			$	40,495			$	173,787			$	102,918
Net income per share — basic		$	0.77			$	0.51			$	2.15			$	1.30
Weighted average shares — basic			80,866				79,864				80,773				79,386
Net income per share — diluted		$	0.77			$	0.50			$	2.13			$	1.27
Weighted average shares — diluted			81,497				81,031				81,655				80,870
Non-GAAP Financial Measures
Net income as reported		$	62,549			$	40,495			$	173,787			$	102,918
Stock-based compensation expense, net of tax (2)			16,829				12,805				49,277				36,973
Net income excluding stock-based compensation (non-GAAP)		$	79,378			$	53,300			$	223,064			$	139,891
Net income per share excluding stock-based compensation (non-GAAP) — diluted		$	0.97			$	0.66			$	2.73			$	1.73
Weighted average shares — diluted			81,497				81,031				81,655				80,870

(1)     Includes stock-based compensation as follows:
Cost of net revenues		$	2,398			$	1,777			$	6,793			$	5,061
Sales and marketing			8,834				6,591				25,926				19,685
Research and development			5,922				4,749				17,399				14,197
General and administrative			5,753				4,289				17,495				12,048
Tax effect of stock-based compensation			(6,078	)			(4,601	)			(18,336	)			(14,018	)
		$	16,829			$	12,805			$	49,277			$	36,973

F5 Networks, Inc.
Condensed Consolidated Statements of Cash Flows
(unaudited, in thousands)

		Nine Months Ended
		June 30,
		2011				2010
Operating activities
Net income		$	173,787			$	102,918
Adjustments to reconcile net income to net cash provided by operating activities:
Realized gain on disposition of assets and investments			(203	)			(117	)
Stock-based compensation			67,613				50,991
Provisions for doubtful accounts and sales returns			453				794
Depreciation and amortization			15,715				17,923
Deferred income taxes			(387	)			10,659
Gain on auction rate securities put option			—				(1,491	)
Loss on trading auction rate securities			—				1,491
Changes in operating assets and liabilities, net of amounts acquired:
Accounts receivable			(43,062	)			3,350
Inventories			874				(3,927	)
Other current assets			8,452				(10,380	)
Other assets			(365	)			(1,651	)
Accounts payable and accrued liabilities			10,086				154
Deferred revenue			62,481				56,507
Net cash provided by operating activities			295,444				227,221
Investing activities
Purchases of investments			(692,812	)			(571,072	)
Sales and maturities of investments			629,766				397,702
Investment of restricted cash			(406	)			(26	)
Acquisition of intangible assets			(80	)			—
Purchases of property and equipment			(20,544	)			(10,119	)
Net cash used in investing activities			(84,076	)			(183,515	)
Financing activities
Excess tax benefits from stock-based compensation			20,221				16,419
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan			21,131				29,338
Repurchase of common stock			(121,526	)			(55,000	)
Net cash used in financing activities			(80,174	)			(9,243	)
Net increase in cash and cash equivalents			131,194				34,463
Effect of exchange rate changes on cash and cash equivalents			(144	)			(1,487	)
Cash and cash equivalents, beginning of period			168,754				110,837
Cash and cash equivalents, end of period		$	299,804			$	143,813