Controller placement strategies for a resilient SDN control plane

Software Defined Networking (SDN) provides efficient network control and management by introducing a logically centralized control plane. However, outsourcing of the control plane intelligence to an SDN controller requires reliable switch-to-controller connection. This paper presents two strategies to address the Reliable Controller Placement (RCP) problem, which protect the control plane against single link and node failures and provide seamless failover by exploiting the principles of resilient routing. The first approach considers that switches have to be connected to a controller over two Disjoint Control Paths (RCP-DCP). The second approach considers that switches have to be connected to two Different Controller Replicas (RCP-DCR) over two disjoint paths. Both approaches are finding working and protection control paths of minimum length to enable fast and efficient failover. The two models have been compared with respect to the unprotected scenario, in terms of control path length, expected control path loss in different failure scenarios and average control path availability. The results show that both models RCP-DCP and RCP-DCR improve significantly the resilience of the control plane, while adding very limited penalty to the average control path length. If link failures are the dominating failures, both RCP-DCP and RCP-DCR offer similar performance and the best strategy depends on the topological characteristics and the number of the controllers in the network. RCP-DCR provides additional protection against controller failures and it shows better performance when node failures are dominating or are comparable to link failures.