Hierarchical Policies for Software Defined Networks (HotSDN ’12)

Hierarchical policies are useful in many contexts in which resources are shared among multiple entities. Such policies can easily express the delegation of authority and the resolution of conflicts, which arise naturally when decision-making is decentralized. Conceptually, a hierarchical policy could be used to manage network resources, but commodity switches, which match packets using flow tables, do not realize hierarchies directly. This paper presents Hierarchical Flow Tables (HFT), a framework for specifying and realizing hierarchical policies in software defined networks. HFT policies are organized as trees, where each component of the tree can independently determine the action to take on each packet. When independent parts of the tree arrive at conflicting decisions, HFT resolves conflicts with user-defined conflict-resolution operators, which exist at each node of the tree. We present a compiler that realizes HFT policies on a distributed network of OpenFlow switches, and prove its correctness using the Coq proof assistant. We then evaluate the use of HFT to improve performance of networked applications.