The Controller Placement Problem
Network architectures such as Software-Defined Networks (SDNs) move the control logic off packet processing devices and onto external controllers. These network architectures with decoupled control planes open many unanswered questions regarding reliability, scalability, and performance when compared to more traditional purely distributed systems. This paper opens the investigation by focusing on two specific questions: given a topology, how many controllers are needed, and where should they go? To answer these questions, the authors examine fundamental limits to control plane propagation latency on an upcoming Internet2 production deployment, and then expand their scope to over 100 publicly available WAN topologies.