Shares of Cisco Systems (Nasdaq: CSCO) are plunging after the networking giant's posted an 18 percent drop in profit and fourth consecutive decline in quarterly margins.

As of 9:45 a.m. Cisco shares are down 12.1 percent.

Cisco also warned that its full-year sales figure would come in at the lower end of its earlier range as the company faces growing pressures in its core network switching business.