An Improved PLC-Trie Based Routing Table Design for Variable Length IP Address Lookup

Abstract

An improved routing table lookup method based on path and level compressed tries (PLC-tries) is presented, which is designed to deal with routing tables that include variable length address prefixes. The IPswen address extension scheme is used as a specific example, which provides a variable length addressing space that consists of 8 levels of subspaces with address lengths ranging from 4 bytes to 11 bytes. By extending the trie path compression technique with an extra address length compression, the conventional PLC-trie and its lookup algorithms are adapted to handling IPswen address prefixes in a uniform and efficient manner. The design is implemented in the Linux kernel by rewriting its dynamic trie based IPv4 FIB (forwarding information base) tables, with minimal performance costs in address prefix lookup. The technique would be essential for upgrading the Linux kernel to support IPswen while retaining its full IPv4 interworking and existing sockets API applications, and be applicable for the future Internet technology development as well.