An approach to the translation of software-defined network switch flow table into network processing unit assembly language

This paper considers the OpenFlow 1.3 switch based on a programmable network processing unit (NPU). OpenFlow switch performs flow entry lookup in a flow table by the values of packet header fields to determine actions to apply to incoming packet (classification). In the considered NPU assembly language, lookup operation may be implemented on the basis of search trees. But these trees cannot be directly used for OpenFlow classification because of compared operands width limitation. In this paper, we propose flow table representation designed for easy translation into NPU search trees. Another goal was to create a compact program that fits in NPU memory. Another NPU limitation requires program updating after each flow table modification. Consequently, the switch must maintain the current flow table state to provide a fast NPU program update. We developed algorithms for incremental update of flow table representation (flow addition and removal). To evaluate the proposed flow table translation approach, a set of flow tables was translated into NPU assembly language using a simple algorithm (based on related work) and an improved algorithm (our proposal). Evaluation was performed on the NPU simulation model and showed that our approach effectively reduces program size.