For intra/inter-AS option B the root is not visible on the leaf. LDP is responsible for building the recursive FEC and signaling the FEC to ABR/ASBR on the leaf. The ABR/ASBR needs to have the PMSI AD router to re-build the FEC (recursive or basic) depending on if they are connected to another ABR/ASBR or to a root node. LDP must import the MVPN PMSI AD routes. To reduce resource usage, importing of the MVPN PMSI AD routes is done manually using the configure router ldp import-pmsi-routes mvpn command. When enabled, LDP requests BGP to provide the LDP task with all of the MVPN PMSI AD routes and LDP caches these routes internally. If import-pmsi-routes mvpn is disabled, MVPN discards the cached routes to save resources.
The import-pmsi-routes mvpn command is enabled if there is an upgrade from a software version that does not support this inter-AS case. Otherwise, by default import-pmsi-routes mvpn is disabled for MVPN inter-AS, MVPN intra-AS, and EVPN, so LDP does not cache any MVPN PMSI AD routes.