To ensure high availability, datacenter networks must rely on local fast
rerouting mechanisms that allow routers to quickly react to link failures, in a
fully decentralized manner. However, configuring these mechanisms to provide a
high resilience against multiple failures while avoiding congestion along
failover routes is algorithmically challenging, as the rerouting rules can only
depend on local failure information and must be defined ahead of time. This
paper presents a randomized local fast rerouting algorithm for Clos networks,
the predominant datacenter topologies. Given a graph G=(V,E) describing a
Clos topology, our algorithm defines local routing rules for each node v∈V, which only depend on the packet's destination and are conditioned on the
incident link failures. We prove that as long as number of failures at each
node does not exceed a certain bound, our algorithm achieves an asymptotically
minimal congestion up to polyloglog factors along failover paths. Our lower
bounds are developed under some natural routing assumptions