A TCAM Index Scheme for IP Address Lookup

Abstract

The rapidly increasing number of hosts on the Internet has caused a significant growth of the number of entries in the routing table, which greatly exacerbates the pressure on TCAM space requirement. In this paper, we propose a novel lookup algorithm: TCAM index scheme (TIS) for IP lookup. The algorithm fully considers the discrepancies among different parts of the prefix tree, and divides the whole prefix tree into several different sub-trees. For each sub-tree, only a single prefix will be stored in the TCAM, while the information of other prefixes (in the sub-tree) is preserved in the correlated SRAM. Hence, the space demand for TCAM is extremely reduced. Meanwhile, bitmap compression is utilized to maximize the compression ratio and minimize average SRAM requirement. Viable implementations on software and hardware plane respectively are also provided. The simulation result shows that for a real-world IPv4 routing table containing 190k prefixes, our scheme can realize line-speed lookup with only 40k 72 bits TCAM entries and 1 MB SRAM. The compression ratio is even higher under IPv6 routing table. What's more, updating is more effective than traditional TCAM-based methods.