CRAFT: A Cache Reduction Architecture for Flow Tables in Software-Defined Networks

Abstract

Software-Defined Networks (SDN) rely on flow tables to forward packets from different flows with different policies. To speed up packet forwarding, the rules in the flow table should reside in the forwarding plane as much as possible to reduce the chances of consulting the SDN controller, which is a slow process. The rules are usually cached in the forwarding plane with a Ternary Content Addressable Memory (TCAM) device. However, using a TCAM with a large capacity is not quite feasible because it is expensive and power-hungry. As a result, wise caching of a subset of flow rules in TCAM has become an important and challenging issue. In this paper, we propose a two-stage caching architecture called CRAFT for the flow table, which can achieve higher cache hit ratio compared to existing rule caching architectures given the same TCAM capacity. CRAFT achieves this by reducing the chances of accommodating multiple overlapped rules in the cache, which is the main source of high caching requirement in existing works. Simulation results show that CRAFT outperforming CacheFlow, the state-of-the-art architecture, by 30% in terms of hit ratio on average.