Binary search schemes for fast IP lookups

IP route look up is the most time consuming operation of a router. Route lookup is becoming a very challenging problem due to the increasing size of routing tables. To reduce the number of entries, routing tables store variable length address prefixes. To determine the outgoing port for a given address, the longest matching prefix amongst all the prefixes, needs to be determined. This makes the task of searching in a large database even more difficult. Our paper describes binary search schemes that allow fast address lookups. Binary search can be performed on the number of entries or on the number of mutually disjoint prefixes, which for most practical routing tables is a little less than the number of entries. Lookups can therefore, be performed in O(N) time, where N is number of entries and the amount of memory required to store the binary database is also O(N). These schemes scale very well with both large databases and for longer addresses (as in IPv6). Keywords—Address Lookup, Binary Search, Longest Prefix Match