Low power fast and dense longest prefix match content addressable memory for IP routers

Abstract

An IP router determines the next hop for an internet protocol packet by finding the longest prefix match. Ternary CAMs, which allow bit masking of the IP address, are commonly used for this fast search function. In this paper, a CAM that directly determines the longest prefix match to the stored address is described. One of these best matching (IPCAM) entries replaces on average 22 TCAM entries. Overall, the resulting IPCAM array is less than 1/10 the size of the equivalent TCAM and dissipates 93.5% less dynamic power. The design automatically produces an encoded prefix match length that is limited by the prefix mask, so entries do not need to be sorted in prefix mask length order. Simulations of extracted layouts in a bulk CMOS 65-nm foundry process show the proposed IPCAM circuits can operate above 1 GHz