Foundry Networks undefined was down 55.7% in early afternoon trading after touching a 52-week low of $13.38. The plunge follows an earnings warning yesterday and downgrades by five analysts. Foundry helped drag down network equipment makers, as did industry giant Cisco Systems (CSCO) , which was down 10.6% after hitting a year's low of $36.50 in the wake of a Merrill Lynch downgrade. Other stocks in the sector fell, including Juniper (JNPR) , down 10.1%; Sycamore Networks (SCMR) , down 16.6% after hitting a low of $32.50 and Extreme Networks (EXTR) , down 29% after a downgrade to neutral from buy by SG Cowen. The Amex Networking Index was down 8.5%.