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Software-Defined Networking (SDN) is introduced to Wide Area Networks (WANs) to facilitate network operations and management. One main advantage of SDN is path programmability, i.e., the ability to change forwarding path of flows by controlling underlying SDN switches to accommodate traffic variations. However, the SDN controllers may experience unexpected failure and thus lose its path programmability. The typical solution is to let active controllers control offline switches, which are controlled by failed controllers, by establishing the remapping between the offline switches and active controllers. However, existing remapping solutions do not consider the impact of controller failure on network performance and cannot exhibit predictable network performance under controller failure. In this paper, we take Traffic Engineering (TE) as a typical network scenario and propose Traffic Engineering-Aware Controller-switcH remapping rEcoveRy named TEACHER. We introduce Traffic-aware Path Programmability (TPP) as a new metric to describe the impact of controller failure on TE and design TEACHER based on this metric to smartly recover offline switches. Simulation results show that TEACHER can increase the overall TPP by up to 83.0% and improves the load balancing performance by up to 58.2% under Sprintlink topology with relatively low computation time, compared with baselines.
Guo et al. (Mon,) studied this question.