Scalable, memory efficient, high-speed lookup and update algorithms for IP routing

IP address lookup algorithms can be evaluated on a number of metrics lookup time, update time, memory usage, and to a lesser extent, the time to construct the data structure used to support lookups and updates. Many of the existing methods are geared towards optimizing a specific metric, and hence do not scale well with the ever expanding routing tables and the forthcoming IPv6 with 128 bit long IP address. In contrast, our effort is directed at simultaneously optimizing multiple metrics and provide solutions that scale well to IPv6. In this paper, we present two IP address lookup schemes Elevator - Stairs algorithm and logW - Elevators algorithm. For a routing table with N prefixes, The Elevator - Stairs algorithm uses optimal O(N) memory, and achieves better lookup and update times than other methods with similar memory requirements. The logW - Elevators algorithm gives O(log W) lookup time, where W is the length of an IP address, while improving upon update time and memory usage. Experimental results using the MAE-West router with 29,487 prefixes show that the Elevator - Stairs algorithm gives an average throughput of 15.7 Million lookups per second (Mlps) using 459 KB of memory, and the logW - Elevators algorithm gives an average throughput of 21.41 Mlps with a memory usage of 1259 KB.