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High availability for Non-stop network controller

Network controller is the core of the OpenFlow-Based Software-Defined Networks (SDN). High availability of network controller is an urgent need objectively. The appearance of controller instance fault should not be perceived by data plane. During the fault recovery, OpenFlow messages, especially asynchronous message from data plane, should not be discarded. Otherwise the control platform would hold the outdated network status. This is an interesting problem which we call Asynchronous Message Discard (ASMD) trouble. This paper proposes a Non-stop network controller (NSNC). It can troubleshoot the ASMD problem based on highly available TCP (HA-TCP) technology. During the fault recovery on distributed control platform, we want to elect the optimal controller to take over the network devices managed by the failed controller instance. We analyses the minimum metrics set for controller election. The view of this paper is verified on Floodlight controller. Experiments show that when the controller instance fails, asynchronous messages from switch will not be discarded, and using HA-TCP only adds negligible overhead to throughput and latency. We test the performance of election algorithm based on Mininet. Currently, there is only a theoretical analysis of metrics related to the election. We will test the validity of the election strategy in a real scenario as part of our future work.