FTLink: Efficient and flexible link fault tolerance scheme for data plane in Software-Defined Networking

Abstract Link fault tolerance has been a hotspot in Software-Defined Networking (SDN) for many years. Both proactive and reactive schemes are proposed to guarantee network availability and robustness. However, the former wastes plenty of Ternary Content Addressable Memory (TCAM) and bandwidth resources, while the latter faces long fault recovery time. In this paper, we propose FTLink, an efficient and flexible link fault tolerance scheme in SDN. Firstly, through collecting the current network state information, we pre-generate a set of backup links for each link of the primary path of the flow. We formulate the backup links planning as a multi-objective optimization problem that minimizes the required switch TCAMs and link bandwidths. Combining flow characteristics, we develop a two-step heuristic algorithm, namely planning backup links for each link that transmits elephant flows with the greedy tracing method in step 1 and for each link that transmits mice flows with the bidirectional searching method in step 2, to determine the backup links set. Then, we introduce a global matching table in the controller to maintain the generated backup links and additional flow rules. Once monitoring a faulty link, FTLink looks up the matching table entries and enables the backup links via installing the additional flow rules into the switches to realize flexible fault recovery. Simulations show that FTLink is effective in terms of high-efficiency TCAM and bandwidth usage and produces an acceptable recovery time of less than 30 ms, compared with baseline schemes. The prototype tests under realistic network further confirm the efficiency of FTLink.