Abstract: The POF protocol is a southbound interface protocol of SDN. Compared with the classic OpenFlow protocol, POF is protocol-independent and flexible. In recent research on the POF protocol, scholars have added actions and instructions such as comparison and jump to the POF, making each table entry more powerful. However, the increase in the number of instructions and functions has also brought greater instability to the interpretation and execution of entry instructions and actions by software switches. The purpose of this article is to improve the robustness of the system by statically checking for situations that cause software switches to crash in advance. We first analyze the characteristics of the POF matching action table and design a specific detection scheme. Then a control flow graph-based detection algorithm is proposed to find instruction errors, unreachable instructions, and loop blocks in the entries. Further, for a cyclic block, a detection algorithm based on a strongly connected component is proposed to determine the validity of the cyclic block. Experiments on POF switches show that the scheme described in this article can accurately detect common entry errors and provide reliability for software switches. At the same time, the detection is light and fast, so that it can detect flow table entries in real time.

Key words: static detection, POF protocol, flow table entry, control flow graph, strongly connected component