Progressive hashing for packet processing using set associative memory

As the Internet grows, both the number of rules in packet filtering databases and the number of prefixes in IP lookup tables inside the router are growing. The packet processing engine is a critical part of the Internet router as it is used to perform packet forwarding (PF) and packet classification (PC). In both applications, processing has to be at wire speed. It is common to use hash-based schemes in packet processing engines; however, the downside of classic hashing techniques such as overflow and worst case memory access time, has to be dealt with. Implementing hash tables using set associative memory has the property that each bucket of a hash table can be searched in one memory cycle outperforming the conventional Ternary CAMs in terms of power and scalability. In this paper we present "Progressive Hashing" (PH), a general open addressing hash-based packet processing scheme for Internet routers using the set associative memory architecture. Our scheme is an extension of the multiple hashing scheme and is amendable to high-performance hardware implementation with low overflow and low memory access latency. We show by experimenting with real IP lookup tables and synthetic packet filtering databases that PH reduces the overflow over the multiple hashing. The proposed PH processing engine is estimated to achieve an average processing speed of 160 Gbps for the PC application and 320 Gbps for the PF application.