Software-Defined Networking (SDN) provides great opportunities to improve the network performance of Wide Area Networks (WANs). In Software-Defined WANs (SD-WANs), SDN controllers dynamically route flows based on network status by managing underlying switches. However, under controller failures in SD-WANs, existing solutions are unadaptable and thus cannot efficiently map offline switches, which were controlled by failed controllers, to active controllers. Thus, flows, which traverse offline switches, become offline and lose their programmability, which means they cannot be rerouted to accommodate to traffic variation. Consequently, the network programmability degrades. In this paper, we propose Matchmaker, an adaptive solution to recover offline flows under controller failures in SD-WANs. Matchmaker smartly changes the paths of some offline flows to adjust the control cost of offline switches based on given control ability of active controllers. As a result, Matchmaker can efficiently map offline switches to active controllers and increase the number of recovered flows. The simulation results show that Matchmaker outperforms existing solutions by increasing the number of recovered offline flows up to 45% under ATT topology and up to 77% under Belnet topology.

软件定义网络（SDN）为改善广域网（WAN）的网络性能提供了巨大的机会。在软件定义的WAN（SD-WAN）中，SDN控制器通过管理基础交换机来根据网络状态动态路由流。但是，在SD-WAN中控制器出现故障的情况下，现有解决方案是不适应的，因此无法将由故障控制器控制的脱机交换机有效地映射到活动控制器。因此，穿越脱机交换机的流变为脱机并失去其可编程性，这意味着它们无法重新路由以适应流量变化。因此，网络可编程性降低。在本文中，我们提出了Matchmaker，这是一种自适应解决方案，可在SD-WAN中的控制器故障下恢复离线流量。Matchmaker可根据活动控制器的给定控制能力，智能地更改某些脱机流的路径，以调整脱机开关的控制成本。结果，Matchmaker可以有效地将脱机交换机映射到活动控制器，并增加已恢复流量的数量。仿真结果表明，Matchmaker在ATT拓扑结构下将恢复的脱机流数量增加到45％，在Belnet拓扑结构下将其恢复到77％，从而优于现有解决方案。