Relaxed multiple routing configurations: IP fast reroute for single and correlated failures

Multi-topology routing is an increasingly popular IP network management concept that allows transport of different traffic types over disjoint network paths. The concept is of particular interest for implementation of IP fast reroute (IP FRR). The authors have previously proposed an IP FRR scheme based on multi-topology routing called multiple routing configurations (MRC). MRC supports guaranteed, instantaneous recovery from any single link or node failure in biconnected networks as well as from many combined failures, provided sufficient bandwidth on the surviving links. Furthermore, in MRC different failures result in routing over different network topologies, which gives a good control of the traffic distribution in the networks after a failure. In this paper we present two contributions. First we define an enhanced IP FRR scheme which we call "relaxed MRC" (rMRC). Through experiments we demonstrate that rMRC is an improvement over MRC in all important aspects. Resource utilization in the presence of failures is significantly better, both in terms of paths lengths and in terms of load distribution between the links. The requirement to internal state in the routers is reduced as rMRC requires fewer backup topologies to provide the same degree of protection. In addition to this, the preprocessing needed to generate the backup topologies is simplified. The second contribution is an extension of rMRC that can provide fast reroute in the presence of multiple correlated failures. Our evaluations demonstrate only a small penalty in path lengths and in the number of backup topologies required.