TaCo: Semantic Equivalence of IP Prefix Tables

Semantically equivalent IP prefix tables exhibit the same forwarding behavior and, thus, can be used in place of each other for the purpose of packet forwarding. Researchers, service providers, and equipment vendors often need to establish this semantic equivalence of prefix tables. Given the large number of IP addresses in use today, either (i) this task takes too long to complete on any available hardware, or (ii) one has to resort to approximation by looking up, in the two tables, only a sample of IP addresses from the entire IP space. We present TaCo (Table Comparison), an algorithm to determine whether or not two given IP prefix tables are semantically equivalent. TaCo is efficient yet accurate, as it guarantees the equivalence result over the entire IP space without explicitly performing a lookup on each IP address over this space. We show that the number of longest prefix matching lookups TaCo needs to perform is bounded by a number that is linear in the sum of the number of entries in the two tables. In practice, for the existing prefix tables in large service providers, the number of longest prefix matchings needed by TaCo does not exceed a few hundred thousand entries.