One of the key design issues for the next generation of IP routers is the IP lookup mechanism. IP lookup is an important action in a router, that is, to find the next hop for each incoming packet with a longest-prefix-match address in the routing table. In this paper, we propose an IP lookup mechanism with the number of memory accesses for an IP lookup being one in the best case and being four in the worst case. The forwarding table needed by our mechanism is small enough to fit in the SRAM. For example, a large routing table with 40000 routing entries can be compacted to a forwarding table of 260KBytes in our scheme.

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