PIM signaling over BIER provides a mechanism to signal PIM join and prune messages through a BIER domain with minimal disruption to the PIM domain routers. The Ingress BIER Boundary Routers (IBBRs) terminate PIM and forward the PIM joins and prunes through the BIER domain to egress at the Egress BIER Boundary Router (EBBR). The EBBR is the closest BIER router to the source.
The PIM signaling messages arriving at the IBBR are encapsulated in a BIER header and forwarded to the EBBR. The EBBR tracks every IBBR that is interested in a specific (S,G). The EBBR forwards the join and prune messages to the PIM domain to which it is attached. When the source receives a join message, it starts the multicast flow for this (S,G). When these PDUs arrive on the EBBR, the EBBR notes all IBBRs that are interested in the (S,G) and adds the IBBRs’ corresponding BIER bits to the BIER header. The EBBR (BFIR) forwards the BIER packets with the PDU as payload to the IBBRs (BFERs), where the BIER header is removed and the packet is forwarded on the interface where the join (S,G) was received.
The following restrictions apply:
PIM signaling through a BIER domain is only supported on FP4.
PIM signaling through a BIER domain is only supported with SSM and not with ASM.
PIM signaling through a BIER domain and MLDP-inband and GTM are mutually exclusive.