CISCO2901/K9-C3 Cisco 2900 Series IEEE 802.1ag/ah/q 512MB RAM 256MB Fl
CMS 512MB (1X512MB) DDR1 2100 266MHZ ECC Registered DIMM Memory Ram Upgrade Compatible with Cisco® 2811 Router Main Memory DMemory Ram Upgrade2811-512D for Server Only - C89 at Amazon.com
128mb DRAM Memory for Cisco 1811 & 1812 Routers (Cisco PN# MEM181X-128U256D) at Amazon.com