As illustrated in Figure: Resolution via ASBR-3, it is possible for the ASBR-1 primary-primary (P-P) LSP to be resolved using ASBR-3, and for the ASBR-2 backup-primary (B-P) LSP to be resolved using the same ASBR-3.
In this case, both the backup-primary LSP and primary-primary LSP are affected when a failure occurs on ASBR-3, as illustrated in Figure: ASBR-3 failure.
In Figure: ASBR-3 failure, the MoFRR can switch to the primary-backup LSP between ASBR-4 and ASBR-1 by detecting BGP MoFRR failure on ASBR-3.
It is strongly recommended that LDP signaling be enabled on all links between the local leaf and local roots, and that all P routers enable ASBR MoFRR and IGP MoFRR. If only LDP signaling is configured, the routing table may resolve a next-hop for LDP FEC when there is no LDP signaling and the primary or backup MoFRR LSPs may not be set up.
ASBR MoFRR guarantees that ASBRs are disjointed, but does not guarantee that the path from the local leaf to the local ASBR are disjointed. The primary and backup LSPs take the best paths as calculated by IGP, and if IGP selects the same path for the primary ASBR and the backup ASBR, then the two LSPs are not disjointed. Ensure that 2 disjointed paths are created to the primary and backup ASBRs.