We've got you covered: Failure recovery with backup tunnels in traffic engineering

Abstract

We present Sentinel, a novel failure recovery system for traffic engineering that pre-computes and installs backup tunnels to improve the robustness of software defined wide area networks (WANs). When a link fails, switches locally redirect traffic to backup tunnels and recover immediately in the data plane, thus substantially reducing the transient congestion compared to reactive rescaling. On the other hand Sentinel completely avoids the bandwidth headroom required by existing proactive approaches like FFC, and improves efficiency of operating the expensive WAN. We make several technical contributions in designing Sentinel. We formulate traffic engineering with backup tunnels (TE-BT) as optimization programs. We propose an approximation algorithm to efficiently solve the problem. We further present a concrete design and implementation of the system based on Openflow group tables for backup tunnels. Extensive experiments on Mininet and numerical simulations show that similar to FFC, Sentinel reduces congestion by 45% compared with rescaling, and its algorithm runs much faster than FFC. Sentinel only introduces a small number of additional forwarding rules and can be readily implemented on today's Openflow switches.