Memory-Efficient IPv4/v6 Lookup on FPGAs Using Distance-Bounded Path Compression

Abstract

Memory efficiency with compact data structures for Internet Protocol (IP) lookup has recently regained much interest in the research community. In this paper, we revisit the classic trie-based approach for solving the longest prefix matching (LPM) problem used in IP lookup. In particular, we target our solutions for a class of large and sparsely-distributed routing tables, such as those potentially arising in the next-generation IPv6 routing protocol. Due to longer prefix lengths and much larger address space, straight-forward implementation of trie-based LPM can significantly increase the number of nodes and/or memory required for IP lookup. Additionally, due to the available on-chip memory and the number of I/O pins of Field Programmable Gate Arrays (FPGAs), state-of-the-art designs cannot support large IPv6 routing tables consisting of over $300$K prefixes. We propose two algorithms to compress the uni-bit-trie representation of a given routing table: (1) \emph{single-prefix distance-bounded path compression} and (2) \emph{multiple-prefix distance-bounded path compression}. These algorithms determine the optimal maximum \emph{skip distance} at each node of the trie to minimize the total memory requirement. Our algorithms demonstrates substantial reduction in the memory footprint compared with the uni-bit-trie algorithm ($1.86\times$ for IPv4 and $6.16\times$ for IPv6), and with the original path compression algorithm ($1.77\times$ for IPv4 and $1.53\times$ for IPv6). Furthermore, implementation on a state-of-the-art FPGA device shows that our algorithms achieve $466$ million lookups per second and are well suited for $100$Gbps lookup. This implementation also scales to support larger routing tables and longer prefix length when we go from IPv4 to IPv6.