BIER -- "Bit Indexed Explicit Replication discussion list"


About BIER
English (USA)

There is a need to simplify network operations for multicast services. Current solutions require a tree-building control plane, which maintains end-to-end tree state per flow, impacting router state capacity and network convergence times. Multi-point tree building protocols are often considered complex to deploy and debug and include mechanics from legacy use-cases and/or assumptions which may no longer apply to the current deployments. When multicast services are transiting a provider network through an overlay, the core network has a choice to either aggregate customer state into a minimum set of core states resulting in flooding traffic to unwanted network end-points, or to map per-customer, per-flow tree state directly into the provider core state amplifying the network-wide state problem.

This mailing list is for a discussion of this topic and the coordination of a potential BoF on the subject of a new architecture for the forwarding of multicast data packets. The goal is to provide optimal forwarding of multicast packets through a "multicast domain" without requiring an explicit tree-building protocol, nor requiring intermediate nodes to maintain any per-flow state. This architecture is known as "Bit Index Explicit Replication" (BIER). When a multicast data packet enters the domain, the ingress router determines the set of egress routers to which the packet needs to be sent. The ingress router then encapsulates the packet in a BIER header. The BIER header contains a bit-string in which each bit represents exactly one egress router in the domain; to forward the packet to a given set of egress routers, the bits corresponding to those routers are set in the BIER header. Elimination of the per-flow state and the explicit tree-building protocols results in a considerable simplification.
BIER may require extensions to IGPs and BGP in addition to the architecture and encapsulation descriptions. For this reason it is expected that BIER will require a dedicated working group which will focus on the overall architecture and shepherd the work toward consensus in the various other location where work is needed.

To see the collection of prior postings to the list, visit the BIER Archives.

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