Abstract: Software defined network (SDN) proposes the architecture of separating the control logic and forwarding devices in networks, which brings the open API for freely programing and makes the network management more fine. However, while the centralized control of SDN brings innovation and convenience for network applications, it also brings other problems, for example the reliability problem and the scalability problem simultaneously. For the problem of control plane’s reliability in SDN, the method that voting deals with the same OpenFlow messages by combing multiple controllers to a quorum view is proposed to tolerate Byzantine faults, which is different from the current OpenFlow protocol. Firstly, we concretely explain the network structure, workflow and exception handling in the application of Byzantine fault-tolerance algorithm with the feature of SDN, and establish the analytical model of multi-controller’s deployment. Secondly, we design a heuristic algorithm to solve the problem of multi-controller’s deployment. Finally, to verify the fault tolerance method and deploy algorithms by simulation, experimental results show that this method can effectively deal with controllers’ faults, improving the reliability of the control layer, but it will sacrifice the system’s performance at some level. Meanwhile, the deployment algorithm can effectively reduce the transmission delay of processing OpenFlow request.

Key words: software defined network (SDN), OpenFlow, Byzantine fault tolerance, reliability, controllers’ deployment