  A reliable and scalable mechanism to provide protection against a link or
node failure has additional requirements in the context of SDN and OpenFlow.
Not only it has to minimize the load on the controller, but it must be able to
react even when the controller is unreachable. In this paper we present a
protection scheme based on precomputed backup paths and inspired by MPLS
crankback routing, that guarantees instantaneous recovery times and aims at
zero packet-loss after failure detection, regardless of controller
reachability, even when OpenFlow's "fast-failover" feature cannot be used. The
proposed mechanism is based on OpenState, an OpenFlow extension that allows a
programmer to specify how forwarding rules should autonomously adapt in a
stateful fashion, reducing the need to rely on remote controllers. We present
the scheme as well as two different formulations for the computation of backup
paths.
