PR-TCAM: Efficient TCAM Emulation on Xilinx FPGAs Using Partial Reconfiguration

Abstract

Modern field-programmable gate arrays (FPGAs) provide a vast amount of logic resources that can be used to implement complex systems while providing the flexibility to modify the design once deployed. This makes them attractive for software-defined networks (SDNs) applications, and, in fact, most vendors provide the building blocks needed for those applications, which include basic packet classification functions such as exact match, longest prefix match, and match with wildcards. Those are needed for different functions such as routing, security filtering, monitoring or quality of service. The match with wildcards can be done using ternary content addressable memories (TCAMs). TCAMs can be implemented as independent standalone devices or as Internet Protocol (IP) blocks that are used inside networking application-specific integrated circuits (ASICs) such as switching ICs. In both cases, the cells of a TCAM are more complex than that of a normal memory and also than that of a binary content addressable memory (CAMs). This is due to the more complex matching that they need to implement. As FPGAs are used in many different applications, it does not make sense to include TCAM blocks inside them as they would be used only in a small fraction of the systems. Therefore, TCAMs are emulated using the logic resources available inside the FPGA. In recent years, a number of schemes to emulate TCAMs on FPGAs have been proposed, some of them based on the use of the logic resources and others on the use of the embedded memory blocks available on the FPGA. In this brief, a technique to efficiently emulate TCAMs on Xilinx FPGAs is presented. The proposed scheme is based on the use of lookup tables (LUTs) and partial reconfiguration to achieve a more effective use of the FPGA resources while supporting the addition and removal of rules. The proposed scheme has been compared to existing implementations and the results show that it can achieve significant savings in resource usage. In addition, it enables the use of all the LUTs in the device for TCAM implementation, something that is not supported by existing approaches that use LUTRAMs.