Tag-In-Tag: Efficient flow table management in SDN switches

Abstract

Ternary Content Addressable Memory (TCAM) with O(1) look up performance has become the obvious and irreplaceable choice of high performance switching hardware. However, emerging network paradigm, especially Software Defined Networking (SDN), has changed the nature of operations and the rate of access in this memory subsystem. These conditions are expected to adversely impact TCAM power consumption, increase the silicon area and hence are likely to bring down the expected performance. In this paper we propose Tag-In-Tag an approach that exploits SDN features and replaces the flow entries with two layers of simpler and shorter tags. One level of tagging exploits the availability of unique path for individual flows from the ingress switch to egress switch that can be computed a-priori. Second level of tagging allows finer identification of the flows to enable flow specific actions. Double tagging helps in preserving the finer benefits of the SDNs while providing highest level of compaction to the flow entries in the flow tables. Through various experiments using real world and synthetic data we show that our approach can accommodate 15 times more flow entries in a fixed size TCAM whereas power consumption per-flow is reduced by 80% compared to an unoptimized SDN enabled switch.