Bit Indexed Explicit Replication
Bit Indexed Explicit Replication WG
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The BIER (Bit Index Explicit Replication) Working Group has defined
an architecture [RFC 8279] for multicast forwarding that uses an
encapsulation [RFC 8296] that can be used on MPLS or Ethernet transport.
The BIER-WG is now chartered to produce Standards Track RFCs, including
the status update for RFCs 8279 and 8296.
The BIER working group's original charter required the publication of an
Informational RFC describing the benefits, problems, and trade-offs for
using BIER instead of traditional multicast forwarding mechanisms as well
as an analysis of the impact and benefit of the BIER data-plane to the
overall Internet architecture. The WG did not produce this RFC, but the
goals of that milestone have nevertheless been reached; i.e., the industry
has demonstrated interest in deploying BIER and the trade-offs are now well
understood. Therefore, BIER is proceeding with work on the Standards Track.
The focus of the BIER-WG is on deployment: transition, partial deployments,
applicability and management.
First and primarily, the BIER-WG will complete its work on:
1) Transition Mechanisms and Partial Deployments: The WG will
describe how BIER can be introduced in existing multicast
networks to shift multicast delivery, either end-to-end or in part
of a network, from mechanisms such as PIM, ng-MVPN, etc. BIER
operation in networks where not all routers are BIER capable
or have other BIER support constraints should be addressed. How
to handle routers supporting BIER with different BitStringLengths
and encapsulations should be addressed. Each new mechanism should
include an applicability statement that clearly describes its
utility and distinctions from already standardized mechanisms.
2) Applicability Statements: The WG will continue to work on
documents describing how BIER can be applied, as has been done
for MVPN in draft-ietf-bier-mvpn. A document describing
applicability to EVPN should be published.
3) Use Case: The WG will produce one use-case document that clearly
articulates the potential benefits of BIER for different use-cases.
4) Manageability and OAM: The WG will describe how OAM will work in
a BIER domain and what simplifications BIER offers for managing the
multicast traffic. A strong preference will be given to extensions to
5) Management models: The WG will work on YANG models to manage BIER.
6) Link-State Routing and BGP extensions: The BIER-WG has already
defined the basic information needed to set up the BIER
forwarding tables via advertisements in OSPFv2 and ISIS; the
extensions to OSPFv3 will be specified. Additional extensions
may be needed - for example, to support constraining the topology
on which a particular BIER sub-domain operates. Any necessary extensions
to the IGP will be specified by the WG as Standards Track, in
cooperation with the LSR WG. The BIER-WG shall also specify the
extensions to support BIER for BGP when used as an IGP (see RFC
7938) and to provide BIER-specific information in BGP-LS, in
cooperation with IDR.
The BIER-WG is additionally chartered to start Standards Track work on:
7) BIER in IPv6 : A mechanism to use BIER natively in IPv6 may be
standardized if coordinated with the 6MAN WG and with understood
8) Forwarding Plane Mechanisms for BIER Traffic Engineering: definition of
how the new BIER forwarding plane structures (e.g. BIFT) can be used to
support engineered multicast trees. No control-plane work will be
done in BIER-WG.
The BIER-WG will serve as a forum to discuss how BIER can be applied.
The BIER-WG will coordinate and collaborate with other WGs as needed. Specific
expected interactions include:
* mpls on the associated MPLS-based OAM mechanisms,
* lsr on OSPF and ISIS extensions to flood BIER-related information,
* babel on Babel extensions to support BIER,
* bess and idr on BGP extensions to flood BIER-related information and the
applicability of existing BGP-based mechanisms for providing multicast group
* pim and mboned on the applicability of and extensions to PIM, IGMP, and MLD to
support BIER operations and transition,
* pce on extensions to program BIER forwarding on the BFIRs,and
* teas on architecture and control-plane mechanisms to use BIER-TE forwarding mechanisms.