Self-configuring loop-free alternates with high link failure coverage

A change in network topology triggers the re-convergence process of routing protocols. The re-convergence time of current routing protocols (e.g. OSPF) is constrained by the possibility of having transient loops due to the independent calculation of shortest paths between routers affected by a network failure. Several IP Fast-ReRoute (IPFRR) schemes have been developed to pro-actively calculate and install alternate forwarding entries almost instantaneously once a topology update message is received, without causing temporary micro-loops. The IPFRR scheme which has been used most extensively so far makes use of Loop-Free Alternates (LFA). While these are easy to configure, LFAs still require manual configuration, and the resulting ratio of covered link failures is only about 60 to 70 percent. This paper presents a logical extension of the Loop-Free Alternate concept, proposes a self-configuring scheme to populate the corresponding alternate entries, and evaluates the performance of the scheme with respect to coverage, configuration time and path length in a simulation environment.