A memory-efficient scheme for address lookup using compact prefix tries

In this paper we present a new memory-efficient scheme for address lookup that exploits the caching support provided by general-purpose processors. We propose Compact Prefix Tries, in which prefixes occurring at multiple levels of a subtrie are compressed into a single node that fits in a single cache line. The scheme performs well in compressing dense as well as sparse tries. For an IP core router (Mae-West) database with 93354 prefixes, the simulation results for Compact Prefix Tries show up to 70% improvement in lookup performance and up to 33% reduction in memory when compared with LC-Tries. In fact, the entire forwarding table for Mae-West required only 829 KB space. Measurements for Compact Prefix Tries, when compared with most existing schemes, show better results in terms of memory usage as well as lookup speeds. Moreover, as the memory usage is significantly less and sparse tries with long paths can be compressed into only a few nodes, this scheme is particularly attractive for IPv6. I. IP ADDRESS LOOKUP PROBLEM The primary role of a router is to route the packet to its destination. In order to do so, for each packet it receives, the router must determine the address of the next hop where it should be forwarded. Router maintains a table called forwarding table that stores the forwarding information. Each entry in the routing table has a network address, length and an output port identifier or next hop address. The pair of address and its length is called as a prefix. When a packet is received, the router extracts the destination address from the packet header. It is then matched with the prefixes in the routing table using some lookup algorithm to find the next hop address. This operation is called as address lookup. Since the prefixes are of different lengths in the router tables, multiple prefixes match a given address. So, in order to find the next hop address for the destination address, the router has to find the most specific prefix or the longest matching prefix. The router then forwards the packet from incoming port to corresponding outgoing port. This is called as switching.