SDNRacer: detecting concurrency violations in software-defined networks

Software-Defined Networking (SDN) control software executes in highly asynchronous environments where unexpected concurrency errors can lead to performance or, worse, reachability errors. Unfortunately, detecting such errors is notoriously challenging, and SDN is no exception. Fundamentally, two ingredients are needed to build a concurrency analyzer: (i) a model of how different events are ordered, and (ii) the memory locations on which event accesses can interfere. In this paper we formulate the first happens-before (HB) model for SDNs enabling one to reason about ordering between events. We also present a commutativity specification of the network switch, allowing us to elegantly capture interference between concurrent events. Based on the above, we present the first dynamic concurrency analyzer for SDNs, called SdnRacer. SdnRacer uses the HB model and the commutativity rules to identify concurrency violations. Preliminary results indicate that the detector is practically effective---it can detect harmful violations quickly.