Path Programmability Recovery under Controller Failures for SD-WANs: Recent Advances and Future Research Challenges

Software-defined networking (SDN) provides new opportunities to improve the performance of modern networks. One of its most prominent application scenarios is in the wide area network (WAN), known as the software-defined wide area network (SD-WAN). SD-WANs leverage the path programmability of the SDN controller to dynam-ically route/reroute network flows, which leads to flexible network scheduling and enhanced network performance. However, controller failures can cause widespread disruption, as flows controlled by the failed controller become offline and lose path programmability, resulting in unpredictable network performance degradation. This article conducts a survey of existing solutions for recovering path pro-grammability under controller failures in SD-WANs. Furthermore, several suggestions to improve exist-ing solutions and outline future research opportuni-ties and challenges are also proposed.