Hashing round-down prefixes for rapid packet classification
USENIX'09 Proceedings of the 2009 conference on USENIX Annual technical conference
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This article deals with a novel architecture for IP routing table construction, on the basis of a single set-associative hash table to support fast longest prefix matching (LPM). The proposed architecture uses two key techniques to lower table storage required drastically: (1) storing transformed prefix representations and (2) accommodating multiple prefixes per table entry via prefix aggregation. Given a set of chosen prefix lengths (called "treads"), all prefixes are rounded down to nearest treads before hashed to the table using their transformed representations so that prefix aggregation opportunities abound in hash entries. Significant table storage reduction makes it possible to fit a large routing table in on-chip SRAM, solving both the memory and bandwidthintensive problems faced by IP routing. Simulation results on real routing tables show that the proposed architecture saves at least two folds of storage when compared with most known hash tablebased design or trie-based design. In addition, our design enjoys fast lookups and incremental updates, with the worst-case lookup time upper-bounded theoretically by the number of treads \zeta) but found experimentally to be 4 memory accesses when\zeta equals 8.