Bit Index Explicit Replication (BIER) is an architecture that provides
multicast forwarding through a "BIER domain" without requiring
intermediate routers to maintain multicast related per-flow state.
Neither does BIER require an explicit tree-building protocol for its
operation. A multicast data packet enters a BIER domain at a "Bit-
Forwarding Ingress Router" (BFIR), and leaves the BIER domain at one
or more "Bit-Forwarding Egress Routers" (BFERs). The BFIR router adds
a BIER header to the packet. Such header contains a bit-string in
which each bit represents exactly one BFER to forward the packet to.
The set of BFERs to which the multicast packet needs to be forwarded
is expressed by the according set of bits set in BIER packet header.
This document describes the OSPF [RFC2328] protocol extension required
for BIER with MPLS encapsulation [RFC8296]. Support for other
encapsulation types is outside thescope of this document. The use of
multiple encapsulation types is outside the scope of this document.