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The most time critical part in packet forwarding is the route lookup which determines the next hop address of the packet. The problem of searching for routes in large databases is compounded by the fact that routing tables store variable length prefixes and their corresponding next hop addresses. In order to forward a packet, routers need to find the longest matching prefix for the destination address. The work presented describes a new fast and efficient algorithm for searching a large database. The scheme described requires several accesses to a small, fast on-chip SRAM and only one access to a slower DRAM in order to determine the next hop address. The paper discusses some of the related work and approaches in performing route lookups. It describes the proposed algorithm where only a single off-chip DRAM access is required to determine the next hop address. It discusses some of the details of the hardware implementation and lists some of the results of the scheme. Some of the design issues are also discussed.
Date of Conference: 2002