BFD can be enabled under the p2mp-sr-tree context for the replication segment next-hops. BFD is enabled at the P2MP SR tree level. The P2MP SR tree registers itself with the current available BFD session. The BFD sessions need to be enabled using other protocols. For example, static route, OSPF, or IS-IS can enable the BFD session on an interface. The replication segments are registered with these BFD sessions. The replication segments cannot initiate a BFD session and rely on other protocols to initiate the BFD session because a replication segment is a unidirectional entity, while BFD is a bidirectional protocol.
When BFD is enabled under the p2mp-sr-tree context, all replication next hops that are using an Layer 3 interface with BFD enabled on that interface register with the BFD module. If the BFD status on the Layer 3 interface goes down, any replication segment next-hop that is using that Layer 3 interface goes operationally down. This operationally down status of the next-hop within a replication segment can cause an FRR.
Only single hop BFD is supported. BFD for unnumbered interfaces is not supported.
For IPv6, protocols such as OSPF or LDP create a BFD session to the link local interface. A static route can create a BFD session to link local or global IPv6 addresses. To use BFD for IPv6 next hops within a replication segment, the replication segment needs to be configured with a link local next-hop for protocols that create the BFD session to the link local address. This way, the replication segment next hop finds a BFD session created by one of these protocols.