Small forwarding tables for fast routing lookups

1 October 1997

journal article
conference paper
Published by Association for Computing Machinery (ACM) in ACM SIGCOMM Computer Communication Review

Vol. 27 (4) , 3-14
https://doi.org/10.1145/263109.263133

Abstract

For some time, the networking community has assumed that it is impossible to do IP routing lookups in software fast enough to support gigabit speeds. IP routing lookups must find the routing entry with the longest matching prefix , a task that has been thought to require hardware support at lookup frequencies of millions per second.We present a forwarding table data structure designed for quick routing lookups. Forwarding tables are small enough to fit in the cache of a conventional general purpose processor. With the table in cache, a 200 MHz Pentium Pro or a 333 MHz Alpha 21164 can perform a few million lookups per second. This means that it is feasible to do a full routing lookup for each IP packet at gigabit speeds without special hardware.The forwarding tables are very small, a large routing table with 40,000 routing entries can be compacted to a forwarding table of 150-160 Kbytes. A lookup typically requires less than 100 instructions on an Alpha, using eight memory references accessing a total of 14 bytes.

Keywords

This publication has 7 references indexed in Scilit:

Fast routing table lookup using CAMs
Published by Institute of Electrical and Electronics Engineers (IEEE) ,2002
Ipsilon Flow Management Protocol Specification for IPv4 Version 1.0
Published by RFC Editor ,1996
Routing on longest-matching prefixes
IEEE/ACM Transactions on Networking, 1996
a ^I t ^P m
ACM SIGCOMM Computer Communication Review, 1995
Towards a Gigabit IP Router
Journal of High Speed Networks, 1992
A Lower Bound on the Complexity of the Union-Split-Find Problem
SIAM Journal on Computing, 1988
PATRICIA—Practical Algorithm To Retrieve Information Coded in Alphanumeric
Journal of the ACM, 1968