In one embodiment, IP lookup into a routing table having prefixes of different prefix lengths is performed by hashing a candidate prefix value to generate a plurality of hash values, where m seed hash values are generated by applying m seed hash functions and one or more additional hash values are generated by combining two or more of the seed hash values in different ways, e.g., using a bit-wise XOR function. The hash values are used to perform membership probes into a Bloom filter programmed with the prefixes corresponding to all of the different prefix lengths in the routing table without having to expand any of the prefixes programmed into the Bloom filter.