FPGA-Based Updatable Packet Classification Using TSS-Combined Bit-Selecting Tree

OpenFlow switches are being deployed in SDN to enable a wide spectrum of non-traditional applications. As a promising alternative to brutal force TCAMs, FPGA-based packet classification is being actively investigated. However, none of the existing FPGA designs can achieve high performance on both search and update for large-scale rule sets. To address this issue, we propose TcbTree, an FPGA-based algorithmic scheme for packet classification. Specifically, at the algorithmic side, i) a two-stage framework consisting of heterogeneous algorithms is proposed, where most rules can be mapped into several balanced trees without rule replications, ii) for the remaining few rules, a centralized TSS (Tuple Space Search) architecture together with a real-time feedback scheme is designed to enhance the efficiency of TSS search on FPGA, and iii) a tree dilution method is designed to equalize rule distribution in trees, so that the latency of tree search can be reduced. At the hardware side, i) an efficient data structure set is designed to convert tree traversal to addressing process, which breaks the constraints of limited tree depth and imbalanced node distribution, and ii) distinct from fully pipelined designs, multiple levels of parallelism are efficiently explored with multi-core, multi-search-engine and coarse-grained pipelines herein. Experimental results using ClassBench show that, with the implementation of TcbTree on FPGA, the average classification throughputs for 1k, 10k, 32k and 100k rule sets achieve 788.8 MPPS, 404.3 MPPS, 237 MPPS and 41.8 MPPS, respectively, and the update throughput for all benchmark rule sets is above 1 MUPS.

I. Introduction

As one major building block of Software-Defined Networking (SDN), OpenFlow has been widely deployed for a wide spectrum of non-traditional applications, such as flexible resource partitioning and real-time migration [2]. An OpenFlow switch applies multiple flow tables for packet match-action lookups and forwarding policies, which essentially falls into a multi-field packet classification problem [3]. Although having been investigated for two decades, this problem encounters new challenging requirements with OpenFlow switches nowadays, including large-scale rule set support and dynamic rule update. Furthermore, in support of the search function, OpenFlow puts forward higher requirements than that in traditional 5-tuples, e.g., with more than 12 fields in OpenFlow 1.x standard [4] or arbitrary number of fields in P4 [5].