Figure 1 shows a scenario in which the EBBR and IBBR are part of the core (backbone) area.
As in the single area scenario, the IBBR attempts to resolve the source IP address, and the IGP calculates the SPF tree to the source. IGP finds that the source IP address (S1) is generated using ABR routers P1 or P3 because these routers are the source routers for S1.
If the EBBR is not the ABR router, the rules of the single area scenario persists and a static route to the multicast source is required. If the EBBR is an ABR, a static route is not required.
Figure 2 shows a scenario in which the BIER domain is in the core AS instead of the core area. The core AS consists of a single area.
The EBBR and IBBRs can be any router in the core AS/area. BGP redistributes its routes into the IGP routers P1, P2, P3, and P4.
