A Comparison of Hashing Schemes for Address Lookup in Computer Networks

The trend toward networks becoming larger and faster, and addresses increasing in size, has impelled a need to explore alternatives for fast address recognition. Hashing is one such alternative which can help minimize the address search time in adapters, bridges, routers, gateways, and name servers. Using a trace of address references, we compared the e ciency of several di erent hashing functions and found that the cyclic redundancy checking (CRC) polynomials provide excellent hashing functions. For software implementation, Fletcher checksum provides a good hashing function. Straightforward folding of address octets using the exclusive-or operation is also a good hashing function. For some applications, bit extraction from the address can be used. Guidelines are provided for determining the size of hash mask required to achieve a speci ed level of performance.