A fast and scalable IP lookup scheme for high-speed networks

One of the key design issues for the next-generation IP routers is the IP lookup mechanism. For each incoming IP packet, the IP routing needs to perform a longest prefix matching on the address lookup in order to determine the packet´s next hop. Currently, the process is done in software and has become a major bottleneck of the router performance. In this paper, we propose a high-speed IP lookup scheme for the best matching prefix (BMP) by using forwarding tables consisting of prefix information tables (PIT) and lookup tables (LT) that provide guidelines for efficient search. The scheme scales very well as the sizes of the address and the routing table increase. For IP lookup in IPv4, the scheme needs 1 memory access in the best case, and 2 memory accesses plus one hash in the worst case to locate the BMP, if one exists. It requires only 560 KBytes to 670 KBytes of memory space when about 45000 routing tables entries in the backbone are logged for simulation. When 50 ns DRAM is used for the forwarding tables, the scheme offers lookup speed of 10 millions packets per second. The lookup speed can be improved linearly with the speedup of the type of memory used.