Optimizing IGP link costs for improving IP-level resilience

Abstract

Abstract-Recently, major vendors have introduced new router platforms to the market that support fast IP-level failure protection out of the box. The implementations are based on the IP Fast ReRoute-Loop Free Alternates (LFA) standard. LFA is simple, unobtrusive, and easily deployable. This simplicity, however, comes at a severe price, in that LFA usually cannot protect all possible failure scenarios. In this paper, we give new graph theoretical tools for analyzing LFA failure case coverage and we seek ways for improvement. In particular, we investigate how to optimize IGP link costs to maximize the number of protected failure scenarios, we show that this problem is NPcomplete even in a very restricted formulation, and we give exact and approximate algorithms to solve it. Our simulation studies show that a deliberate selection of IGP costs can bring many networks close to complete LFA-based protection.

High Availability in the Future Internet

“…In order to solve LFA cost optimization problem, a computationally expensive optimal algorithm as well as efficient approximating heuristics were proposed [40,15]. A brief result can be seen in Table 2, where n and m denote the number of nodes and the number of links in the network, respectively.…”

“…By means of this small modification, the initial LFA failure coverage can be improved by 15%. Additionally, it was also proved in [40] that the average node degree Δ plays an important role to determine the attainable upper bound of LFA failure coverage. As a matter of fact, for any connected graph G with n > 2:…”

“…In a subsequent study [40], another improving approach, called the LFA cost optimization problem, was examined. The problem asks for finding an optimal cost setting in a network, which produces 100% failure case coverage.…”

Optimization methods for improving IP-level fast protection for local shared risk groups with Loop-Free Alternates

“…A plausible choice would be to optimize the IGP link costs [34,40,48], but this would alter shortest paths. In many deployments, touching shortest paths is decidedly ruled out by operators who usually have their own intricate (and often proprietary) operational concerns they want to materialize in the way forwarding Fig.…”

“…There have been various attempts at LFA network optimization recently [34,40,48], one of the most recent of which is LFA graph extension [37,41]. The LFA graph extension problem asks for adding the smallest number of new links to the network so that, on the one hand, LFA failure case coverage becomes 100% and, on the other hand, shortest paths remain intact.…”