P4DB: On-the-fly debugging of the programmable data plane

While extending network programmability to a larger degree, P4 also raises the risks of incurring runtime bugs after the deployment of P4 programs. These runtime bugs, if not handled promptly and properly, can ruin the functionality and performance of networks. Unfortunately, the absence of runtime debuggers makes troubleshooting of P4 program bugs challenging and intricate for operators. This paper is devoted to the on-the-fly debugging of runtime bugs in P4-enabled networks. We propose P4DB, a general debugging platform that empowers operators to debug P4 programs in three levels of visibility by provisioning operator-friendly primitives. By P4DB, operators can use the watch primitive to quickly narrow the debugging scope from network level or device level to table level, then use the break and next primitives to decompose the match-action table into three steps and troubleshoot the runtime bugs step by step. We implemented a prototype of P4DB and evaluated the performance in terms of the data plane, control plane and control channel. On P4-specific programmable data plane, P4DB merely introduces a small throughput penalty (1.3%~13.8%) and imposes a little-increased delay (0.6%~11.9%).