Loop Free Alternates (LFA) or IP Fast Reroute (FRR) crystallized some years ago with a basic specification in [RFC5286]as a noteworthy concept to provide standalone backup path calculations just based on route inequalities.
This post follows-up my previous article Granular BGP advertise-external for MPLS L3VPNs with the intention to tweak and illustrate the BGP add-path feature implementation in Junos OS for IPv4 unicast and IPv6 labeled-unicast (6PE) routes. BGP add-paths provide a more comprehensive path diversity approach than diverse paths or advertise-external and in my view, multiple applications can be based on Junos OS BGP add-path tactical deployment in default instance tables.
In some BGP multi-homed environments between networks, it is possible to achieve shorter convergence times by using certain features beyond traditional [RFC4271] BGP rules. One of these features is the so-called BGP advertise-external or best-external, so that Autonomous System Border Routers (ASBRs) also advertise the best externally received path, even though it may not result as the ultimate best path from the selection algorithm.
A label substitution policy in Junos OS provides resources to conserve and control labels in an inter-AS option B Autonomous System Border Router (ASBR) with local VRFs. It provides further instrumentation to be able to discern routes further than by its Route Targets (RTs) and determine a label action for them.