Resilient Strategies to SDN: An Approach Focused on Actively Replicated Controllers

Software Defined Networking (SDN) are based on the separation of control and data planes. The SDN controller, although logically centralized, should be effectively distributed for high availability. Since the specification of OpenFlow 1.2, there are new features that allow the switches to communicate with multiple controllers that can play different roles -- master, slave, and equal. However, these roles alone are not sufficient to guarantee a resilient control plane and the actual implementation remains an open challenge for SDN designers. In this paper, we explore the OpenFlow roles for the design of resilient SDN architectures relying on multi-controllers. As a proof of concept, a strategy of active replication was implemented in the Ryu controller, using the OpenReplica service to ensure consistent state among the distributed controllers. The prototype was tested with commodity RouterBoards/MikroTik switches and evaluated for latency in failure recovery and switch migration for different workloads. We observe a set of trade-offs in real experiments with varyin workloads at both the data and control plane.