A truly scalable IP lookup algorithm for next generation internet

Continuing growth in traffic, the size of routing table as well as the link speeds puts great challenge on the performance of Internet address lookup. The packet forwarding engine need perform 150 million IP address lookups per second for a 100Gbps line card while accommodating up to 500,000 prefixes and very likely 1M in the near future. TCAM based lookup solutions do not scale well for the next-generation due to its high power dissipation and large footprint. Algorithmic solutions can achieve high throughputs with hardware parallelism and compact storage needs, but can hardly scale simultaneously in the three dimensions of increased table size, throughput, and prefix length as IP moves to 64 bit IPv6 addresses. We propose a novel IPv6 lookup algorithm called Prefix Range Based Binary Search (PRB-BS) using binary search over hash tables organized by the range of prefix length. By eliminating the path information of the subtrie our scheme reduces the memory demands considerably. Besides, the binary search scheme based on prefix range reduces the worst case time of hash lookups to log₂L, with L being the number of subtrie layers. We also introduce asymmetry binary search to further reduce memory demands and memory accesses. Compared with the tree bitmap algorithm widely used by many modern routers the memory requirements of PRB-BS algorithm is about 55% of the tree bitmap algorithm. The experiment results also show that the average search depth of PRB-BS algorithm is stable at 2 with the increased number of prefixes, which reflects better scalability of PRB-BS algorithm.