Universit a Di Pisa Ip Address Lookup Made Fast and Simple Ip Address Lookup Made Fast and Simple

The IP address lookup problem is one of the major bottlenecks in high performance routers. Previous solutions to this problem rst describe it in the general terms of longest preex matching and, then, are experimented on real routing tables T. In this paper, we follow the opposite direction. We start out from the experimental analysis of real data and, based upon our ndings, we provide a new and simple solution to the IP address lookup problem. More precisely, our solution for m-bit IP addresses is a reasonable trade-oo between performing a binary search on T with O(log jTj) accesses, where jTj is the number of entries in T, and executing a single access on a table of 2 m entries obtained by fully expanding T. While the previous results start out from space-eecient data structures and aim at lowering the O(log jTj) access cost, we start out from the expanded table with 2 m entries and aim at compressing it without an excessive increase in the number of accesses. Our algorithm takes exactly three memory accesses and occupies O(2 m=2 + jTj 2) space in the worst case. Experiments on real routing tables for m = 32 show that the space bound is overly pessimistic. Our solution occupies approximately one megabyte for the MaeEast routing table (which has jTj 44; 000 and requires approximately 250 KB) and, thus, takes three cache accesses on any processor with 1 MB of L2 cache. According to the measurement obtained by the VTune tool on a Pentium II processor, each lookup requires 3 additional clock cycles besides the ones needed for the memory accesses. Assuming a clock cycle of 3.33 nanoseconds and an L2 cache latency of 15 nanoseconds, search of MaeEast can be estimated in 55 nanoseconds or, equivalently, our method performs 18 millions of lookups per second. 1. INTRODUCTION Computer networks are expected to exhibit very high performance in delivering data because of the explosive growth of Internet nodes (from 100,000 computers in 1989 to over 30 millions as of today's). The network bandwidth, which measures the number of bits that can be transmitted in a certain period of time, is thus continuously improved by adding new links and/or by improving the performance of the existing ones. Routers are at the heart of the networks in that they forward packets from input interfaces to output interfaces on the ground of the packets' …