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Concise Lookup Tables for IPv4 and IPv6 Longest Prefix Matching in Scalable Routers

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2 Author(s)
Fong Pong ; Broadcom Corp., Santa Clara, CA, USA ; Nian-Feng Tzeng

We present a distinct longest prefix matching (LPM) lookup scheme able to achieve exceedingly concise lookup tables (CoLT), suitable for scalable routers. Based on unified hash tables for handling both IPv4 and IPv6 simultaneously, CoLT excels over previous mechanisms in: 1) lower on-chip storage for lookup tables; 2) simpler table formats to enjoy richer prefix aggregation and easier implementation; and 3) most importantly, deemed the only design able to accommodate both IPv4 and IPv6 addresses uniformly and effectively. As its hash tables permit multiple possible buckets to hold each prefix (following a migration rule to avoid false positives altogether), CoLT exhibits the best memory efficiency and can launch parallel search over tables during every LPM lookup, involving fewer cycles per lookup when on-chip memory is used to implement hash tables. With 16 (or 32) on-chip SRAM blocks clocked at 500 MHz (achievable in today's 65-nm technology), it takes 2 (or 1.6) cycles on average to complete a lookup, yielding 250 (or 310+) millions of packets per second (MPPS) mean throughput. Being hash-oriented, CoLT well supports incremental table updates, besides its high table utilization and lookup throughput.

Published in:

Networking, IEEE/ACM Transactions on  (Volume:20 ,  Issue: 3 )