Bit Indexed Explicit Replication

Project type: Main

BIER is a mechanism to provide multicast routing in an SDN network. As you may know, in a legacy network, there are multicast delivery protocols in L2 and L3, such as PIM, IGMP, DVMRP, MSDP, and so on. These protocols run in a router or switch and help the network node build a state table of multicast flows where they need to be replicated. In SDN and OpenDaylight, multicast delivery is handled by the controller. None of the transit routers and switches need to build a per flow state table, as the controller provides the function and builds a global state table for multicast flows. This simplifies the configuration state of transit switches and routers.

Multicast packets enter a BIER domain via Bit-Forwarding Ingress Router (BFIR) and leave the domain via one or more Bit-Forwarding Egress Routers (BFERs).

When the packets enter the SDN domain, the ingress BEIR router adds a BIER header to the packet. This header is a bit string, where each bit represents exactly one BFER to forward the packet to. A set of BFERs to which the multicast packet needs to be forwarded is expressed by setting the bits that correspond to the routers in the BIER header.

The following diagram explains the BIER domain:

The following diagram explains the BFER header: