Shares of F5 Networks /quotes/comstock/15*!ffiv/quotes/nls/ffiv (FFIV 106.86, -31.92, -23.00%) , which offers products and services for managing Internet traffic, tumbled 20% after the company posted weaker-than-expected results and gave a disappointing forecast.

The company’s report appeared to trigger a selloff in shares of other networking and cloud-computing-focused firms.

It was “an unusually cloudy quarter from F5 Networks,” Ticonderoga analyst Brian White said in a note. “F5 [is] likely to set off a ‘Cloud Burst.’”

Indeed, shares of Cisco Systems Inc. /quotes/comstock/15*!csco/quotes/nls/csco (CSCO 20.60, -0.23, -1.08%)  , NetApp Inc. /quotes/comstock/15*!ntap/quotes/nls/ntap (NTAP 55.60, -2.04, -3.53%)  , Juniper Networks Inc. /quotes/comstock/13*!jnpr/quotes/nls/jnpr (JNPR 34.55, -2.35, -6.37%)  and EMC Corp. /quotes/comstock/13*!emc/quotes/nls/emc (EMC 23.60, -0.64, -2.64%)  all fell in early trading.

“Maybe the weakness discussed by Cisco Systems back in November doesn’t seem so crazy anymore,” White added, referring to Cisco’s description of pockets of weakness in the corporate tech market.

Meanwhile, shares of Seagate /quotes/comstock/15*!stx/quotes/nls/stx (STX 13.19, -0.94, -6.65%)  slid more than 6% after the hard-disk-drive company reported a 72% drop in quarterly profit. The company’s report also highlighted worries about the direction of the PC market and the negative impact of the rising tablet category on the space.

“There is still some weakness in the consumer spending environment, which impacts PC sales and thus [hard-disk-drive] sales,” Wedbush analyst Kaushik Roy said in a note. “The tablet market is new, and it is hard to forecast the demand and the corresponding cannibalization of the notebook market in the next 12 months.”

The double whammy from Seagate and F5 highlighted the sector’s decline. The Nasdaq Composite Index /quotes/comstock/10y!i:comp (COMP 2,694, -31.59, -1.16%)  lost almost 1% to 2,706. The Morgan Stanley High Tech 35 Index /quotes/comstock/10t!msh.x (MSH 682.26, -11.06, -1.60%)  and the Philadelphia Semiconductor Index /quotes/comstock/10y!i:sox (SOX 431.04, -8.29, -1.89%)  were each down more than 1%.

The sector got a boost from eBay Inc. /quotes/comstock/15*!ebay/quotes/nls/ebay (EBAY 30.39, +1.29, +4.43%) which rose more than 4% after the Internet auction company reported results that beat Wall Street’s expectations.