SafeGuard: Congestion and Memory-aware Failure Recovery in SD-WAN

In software-defined WANs (SD-WAN), link failure can lead to congestion and packet loss, hence degrading application performance. State-of-the-art traffic engineering approaches can speed up failure recovery by proactively installing backup tunnels and redirecting affected traffic immediately in the data plane, which reduces the burden on the network controller. However, these approaches either lead to bandwidth waste because of reserved link capacity or impose restrictions on network topologies, e.g., the existence of link-disjoint routes or large switch memory resources. In this paper, we propose SafeGuard, a software-defined proactive recovery system that improves bandwidth allocation and switch-memory usage while working on any connected network. We formulate the failure recovery problem as a multi-objective MILP optimization problem for all possible single link failures, the most common case in current WANs as temporally-coinciding failures are rare. We then develop a heuristic to efficiently compute backup routes as the problem is NP-Hard. We implemented a prototype of SafeGuard using the Ryu SDN controller and extensively evaluate it in Mininet over two real topologies, Google B4 and ATT. Our results show that SafeGuard can reduce the number of congested links by up to 50% compared to the state-of-the-art failure recovery scheme.