When Raft Meets SDN

Abstract

In SDN, the logically centralized control plane ("network OS") is often realized via multiple SDN controllers for scalability and reliability. ONOS is such an example, where it employs Raft -- a new consensus protocol developed recently -- for state replication and consistency among the distributed SDN controllers. The reliance of network OS on consensus protocols to maintain consistent network state introduces an intricate inter-dependency between the network OS and the network under its control, thereby creating new kinds of fault scenarios or instabilities. In this paper, we use Raft to illustrate the problems that this inter-dependency may introduce in the design of distributed SDN controllers and discuss possible solutions to circumvent these issues.