Path Restoration in Source Routed Software Defined Networks

Software defined networks have a central controller and central view of the network, allowing for source routing to be used as a scalable routing technique instead of the traditional destination based forwarding. However, with source routing the switches are reduced to simple forwarding devices, incapable of finding alternate paths in the event of link failures. In this paper we look at techniques to provide resiliency when packets are in transit and a network link failure occurs. Path restoration is one such mechanism wherein we use a bypass path for the failed link. Such bypass paths are stored locally on each of the switches, for all of its outgoing links. This mechanism ensures that the recovery mechanism is scalable since it avoids contacting the controller and takes local corrective measures. We have proposed two approaches for storing the bypass paths. In the first method we store the bypass path between all pairs of nodes. In the second method we store the bypass paths between few selected nodes. These node are the two hop neighbors, chosen using either the two colorable graph approach or the vertex cover approach. Our analysis shows that the second method, using the vertex cover approach reduces the total number of bypass paths stored, without compromising the resiliency. Also our solutions are topology dependent and not path dependent, allowing for most of the computations to be done proactively.