A multicast BIER network can be divided into three layers:
routing underlay (IGP) has the following capabilities:
establishes BIER adjacencies based on BIER configuration
populates BIER routing table (best path reachability)
provides routing-underlay-based redundancy and convergence, ECMP
BIER layer (BIER routing table, BIER header) has the following capabilities:
advertises and configures the BFR prefix and BIER ID (bitmask bit) for BIER routers
imposes a new BIER header (bitmask: "OR" for receiver PEs based on their BIER IDs as dictated by multicast flow overlay)
forwards multicast traffic using the BIER header and BIER routing table
prevents loops and duplication by using bitmask manipulation and removing the bits for PEs that are not reachable using the L3 interface next hop
Multicast flow overlay (MVPN, BGP) uses MP-BGP to distribute and discover the endpoints (RFC-6513 and RFC-6514).