On providing fast protection with remote loop-free alternates

Abstract

Up to not so long ago, loop-free alternates (LFA) was the only viable option for providing fast protection in pure IP and MultiProtocol Label Switching---Label Distribution Protocol networks. Unfortunately, LFA cannot provide protection for all possible failure cases in general. Recently, the Internet Engineering Task Force has initiated the remote loop-free alternates (rLFA) technique as a simple extension to LFA, to boost the fraction of failure cases covered by fast protection. Before further standardization and deployment, however, it is crucial to determine to what extent rLFA can improve the level of protection against single link or node failures in a general IP network, as well as to find optimization methods to tweak a network for 100 % rLFA coverage. In this paper, we take the first steps towards this goal by solving these problems in the special, but practically relevant, case when each network link is of unit cost. We also provide preliminary numerical evaluations conducted on real IP network topologies, which suggest that rLFA significantly improves the level of protection, and most networks need only 2---3 new links to be added to attain 100 % failure case coverage irrespectively of whether link or node protection is considered.