Loop-Free Alternates selection for Multi-Homed Prefixes

Deployment experience gained from implementing algorithms to determine Loop-Free Alternates (LFAs) for multi-homed prefixes has revealed some avenues for potential improvement. This document provides explicit inequalities that can be used to evaluate neighbors as a potential alternates for multi-homed prefixes. It also provides detailed criteria for evaluating potential alternates for external prefixes advertised by OSPF ASBRs. This documents updates and expands some of the "Routing Aspects" as specified in Section 6 of RFC 5286.