Policy Based Loop Free Alternate(LFA) routes for OSPF

Support for OSPF loop-free alternate (LFA) routes essentially adds IP fast-reroute capability for OSPF. The device precomputes multiple loop-free backup routes for all OSPF routes. These backup routes are preinstalled in the Packet Forwarding Engine, which performs a local repair and implements the backup path when the link for a primary next hop for a particular route is no longer available. The selection of LFA is done randomly by selecting any matching LFA to progress to the given destination. This does not ensure best backup coverage available for the network. In order to choose the best LFA, you can configure network-wide backup selection policies for each destination (IPv4 and IPv6) and a primary next-hop interface. These policies are evaluated based on admin-group, srlg, bandwidth, protection-type, metric, and neighbor information. During backup shortest-path-first (SPF) computation, each node and link attribute of the backup path is accumulated by the IGP and is associated with every node (router) in the topology. The next hop in the best backup path is selected as the backup next hop in the routing table. In general, backup evaluation policy rules are categorized into the following types: * Pruning-Rules configured to select the eligible backup path. * Ordering-Rules configured to select the best among the eligible backup paths. The backup selection policies can be configured with both pruning and ordering rules. While evaluating the backup policies, each backup path is assigned a score, an integer value that signifies the total weight of the evaluated criteria. The backup path with the highest score is selected.