Routing optimization for IP networks with loop-free alternates

Loop-free alternates (LFAs) have been developed for fast reroute (FRR) in intradomain IP networks. They are simple, standardized, and already offered by several vendors. However, LFAs have two major drawbacks. They often cannot provide failure protection against all single link or node failures in spite of physical connectedness, and some LFAs cause routing loops in scenarios with node or multiple failures.LFAs may be applied for various reasons that we call applications in this work. We propose several definitions for LFA coverage that quantify the application-specific utility of LFAs available in the network. The availability of LFAs and whether they can cause routing loops heavily depend on the IP routing which is determined by the choice of administrative IP link costs. To maximize the benefit of LFA usage, we optimize the IP link costs using LFA coverage as objective function. We demonstrate the feasibility and effectiveness of that approach in several test networks, and show that the choice of the right optimization function is crucial to maximize LFA coverage. However, maximizing LFA coverage can lead to significant traffic imbalance and may result in high link loads. Therefore, we suggest Pareto-optimization and demonstrate that resulting link costs can lead to both high LFA coverage and low link loads.