BGP Link-State extensions for BIER
draft-ietf-bier-bgp-ls-bier-ext-21

BIER Working Group                                               R. Chen
Internet-Draft                                                  Z. Zhang
Intended status: Standards Track                         ZTE Corporation
Expires: 11 July 2026                                        V. Govindan
                                                                   Cisco
                                                            IJ. Wijnands
                                                              Individual
                                                                Z. Zhang
                                                        Juniper Networks
                                                          7 January 2026

                   BGP Link-State extensions for BIER
                   draft-ietf-bier-bgp-ls-bier-ext-21

Abstract

   Bit Index Explicit Replication (BIER) is an architecture that
   provides optimal multicast forwarding through a "BIER domain" without
   requiring intermediate routers to maintain any multicast related per-
   flow state.  BIER also does not require any 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.  The BIER header
   contains a bitstring 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 setting the bits that
   correspond to those routers in the BIER header.

   BGP Link-State (BGP-LS) enables the collection of various topology
   informations from the network, and the topology informations are used
   by the controller to calculate the fowarding tables and then
   propagate them onto the BFRs(instead of having each node to calculate
   on its own) and that can be for both inter-as and intra-as
   situations.

   This document specifies extensions to the BGP Link-state address-
   family in order to advertise the BIER informations.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  BGP-LS Extensions for BIER  . . . . . . . . . . . . . . . . .   3
     2.1.  Prefix Attributes TLVs  . . . . . . . . . . . . . . . . .   4
     2.2.  The BIER information TLV  . . . . . . . . . . . . . . . .   4
     2.3.  The BIER MPLS Encapsulation TLV . . . . . . . . . . . . .   5
     2.4.  The BIER non-MPLS Encapsulation TLV . . . . . . . . . . .   6
   3.  Equivalent IS-IS BIER TLVs/Sub-TLVs . . . . . . . . . . . . .   7
   4.  Equivalent OSPFv2/OSPFV3 BIER TLVs/Sub-TLVs . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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1.  Introduction

   Bit Index Explicit Replication (BIER) is an architecture that
   provides optimal multicast forwarding through a "BIER domain" without
   requiring intermediate routers to maintain any multicast related per-
   flow state.  BIER also does not require any 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.  The BIER header
   contains a bitstring 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 are expressed by setting the bits that
   correspond to those routers in the BIER header.

   The BGP-LS address-family/sub-address-family have been defined to
   allow BGP to carry Link-State informations.  This document specifies
   extensions to the BGP Link-state address-family in order to advertise
   BIER-specific informations, Similar to BGP-LS Advertisement of IGP
   Traffic Engineering Performance Metric Extensions([RFC8571]).  An
   external component (e.g., a controller/a PCE(see [RFC4655] for PCE-
   Based Architecture ,[RFC5440] for PCEP and [RFC5376] for Inter-AS
   Requirements for the PCEP.))then can learn the BIER informations in
   the "northbound" direction and calculate BIRT/BIFT and then propagate
   them onto BFRs (instead of having each BFR to calculate on its own),
   and that can be for both inter-as and intra-as situations.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  BGP-LS Extensions for BIER

   [RFC8279] defines the BFR - A router that supports BIER is known as a
   "Bit-Forwarding Router"(BFR), and each BFR MUST be assigned a "BFR-
   Prefix".  A BFR's Prefix MUST be an IP address (either IPv4 or IPv6)
   of the BFR, and MUST be unique and routable within the BIER domain as
   described in section 2 of [RFC8279], and then external component
   (e.g., a controller) need to collect BIER informations of BIER
   routers are associated with the BFR-Prefix in the "northbound"
   direction within the BIER domain.

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   Given that the BIER informations are associated with the prefix, the
   Prefix Attribute TLV [RFC9552] can be used to carry the BIER
   informations.  The new Prefix Attribute TLVs are defined for the
   encoding of BIER informations.

2.1.  Prefix Attributes TLVs

   The following Prefix Attribute TLVs are defined:

   +======+=============================+=============+
   | Type |         Description         |   Section   |
   +======+=============================+=============+
   | TBD1 |       BIER information      | section 3.2 |
   +------+-----------------------------+-------------+
   | TBD2 |   BIER MPLS Encapsulation   | section 3.3 |
   +------+-----------------------------+-------------+
   | TBD3 | BIER non-MPLS Encapsulation | section 3.4 |
   +------+-----------------------------+-------------+
          Table 1: The new Prefix Attribute TLVs

2.2.  The BIER information TLV

   A new Prefix Attribute TLV (defined in [RFC9552] is defined for
   distributing BIER informations.  The new TLV is called the BIER
   information TLV.  The BIER information TLV may appear multiple times.

   The following BIER information TLV is defined:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | subdomain-id  |             BFR-ID            |  Reserved     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    BAR        |    IPA        |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 1: The BIER information TLV

   Type: A 2-octet field with value TBD, see IANA Considerations
   section.

   Length: 2 octets.

   Subdomain-id: Unique value identifying the BIER sub-domain, 1 octet.

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   BFR-ID: A 2-octet field encoding the BFR-ID, as documented in
   [RFC8279].  If the BFR-ID is zero, it means, the advertising router
   is not advertising any BIER-id.In some environment, BFR-ID can be
   configured by NMS, The BFR-ID should be sent to a controller.

   BAR: A 1-octet field encoding the BIER Algorithm, used to calculate
   underlay paths to reach BFERs.  Values are allocated from the "BIER
   Algorithms" registry which are defined in [RFC8401], [RFC8444]and
   [I-D.ietf-bier-ospfv3-extensions].

   IPA: A 1-octet field encoding the IGP Algorithm, used to either
   modify,enhance, or replace the calculation of underlay paths to reach
   BFERs as defined by the BAR value.  Values are from the "IGP
   Algorithm" registry.

   Reserved: MUST be 0 on transmission, ignored on reception.  May be
   used in future versions.

2.3.  The BIER MPLS Encapsulation TLV

   The BIER MPLS Encapsulation TLV is used in order to advertise MPLS
   specific informations used for BIER.  It MAY appear multiple times.

   In some environment, each router allocates its labels, and advertises
   it to the controller.  That solution is simpler as the controller
   does not need to deal with label allocation.  If the controller has
   to deal with Label allocation , there needs to be a (global) range
   carved out such there are no conflicts.  We can avoid all that by
   having the router allocate the BIER Label range and advertise it to
   the controller.

   The following the BIER MPLS Encapsulation Sub-TLV is defined:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Type               |                Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Max SI   |BS Len |              Label                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Reserved                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 2: The BIER MPLS Encapsulation TLV

   Type: A 2-octet field with value TBD, see IANA Considerations
   section.

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   Length: 2 octets.

   Max SI: A 1-octet field encoding the maximum Set Identifier(as
   defined in [RFC8279]), used in the encapsulation for this BIER
   subdomain for this BitString length.

   Label: First label of the range, 20 bits.  The labels are as defined
   in [RFC8296].

   BS Len: A 4-bit field field encoding the Bitstring length as per
   [RFC8296].

   BS length in multiple BIER MPLS Encapsulation Sub-TLV associated with
   the same BIER Sub-TLV MUST NOT repeat, otherwise only the first BIER
   MPLS Encapsulation Sub-TLV with such BS length MUST be used and any
   subsequent BIER MPLS Encapsulation Sub-TLVs with the same BS length
   MUST be ignored.

2.4.  The BIER non-MPLS Encapsulation TLV

   The BIER non-MPLS Encapsulation TLV is used in order to advertise
   non-MPLS encapsulation(e.g. ethernet encapsulation ) capability and
   other associated parameters of the encapsulation.It MAY appear
   multiple times.

   The following the BIER non-MPLS Encapsulation Sub-TLV is defined:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Max SI    |BS Len |               BIFT-id                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Figure 3: The BIER non-MPLS Encapsulation TLV

   Type: A 2-octet field with value TBD, see IANA Considerations
   section.

   Length: 2 octets.

   Max SI: A 1-octet field encoding the maximum Set Identifier(as
   defined in [RFC8279]), used in the encapsulation for this BIER
   subdomain for this BitString length.

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   BIFT-id: A 20 bit field encoding the first BIFT-id of the BIFT-id
   range.

   The "BIFT-id range" is the set of 20-bit values beginning with the
   BIFT-id and ending with (BIFT-id + (Max SI)).  A unique BIFT-id range
   is allocated for each BitString length and sub-domain-id.  These
   BIFT-id's are used for BIER forwarding as described in [RFC8279])and
   [RFC8296].

   Local BitString Length (BS Len): A 4-bit field encoding the Bitstring
   length as per [RFC8296].

   Reserved:SHOULD be set to 0 on transmission and MUST be ignored on
   reception.

3.  Equivalent IS-IS BIER TLVs/Sub-TLVs

   This section illustrates the IS-IS BIER Extensions Sub-TLVs/Sub-Sub-
   TLVs mapped to the ones defined in this document.

   The following table illustrates for each BGP-LS TLV, and its
   equivalence in IS-IS.

   +=============+=============+=======================================+
   | Description |  IS-IS TLV/ |               Reference               |
   |             |   Sub-TLV   |                                       |
   +=============+=============+=======================================+
   |     BIER    |  BIER info  |               [RFC8401]               |
   | information |   Sub-TLV   |                                       |
   +-------------+-------------+---------------------------------------+
   |  BIER MPLS  |  BIER MPLS  |               [RFC8401]               |
   |Encapsulation|Encapsulation|                                       |
   |             | Sub-Sub-TLV |                                       |
   +-------------+-------------+---------------------------------------+
   |BIER non-MPLS|BIER non-MPLS|[I-D.ietf-bier-lsr-non-mpls-extensions]|
   |Encapsulation|Encapsulation|                                       |
   |             | Sub-Sub-TLV |                                       |
   +-------------+-------------+---------------------------------------+
        Table 2: IS-IS BIER Extensions Sub-TLVs/Sub-Sub-TLVs

4.  Equivalent OSPFv2/OSPFV3 BIER TLVs/Sub-TLVs

   This section illustrates the BIER Extensions TLVs/Sub-TLVs mapped to
   the ones defined in this document.

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   The following table illustrates for each BGP-LS TLV, and its
   equivalence in OSPFv2/OSPFV3.

   +=============+=============+=======================================+
   | Description |OSPFv2/OSPFV3|           Reference                   |
   |             | sub-TLV/Sub-|                                       |
   |             |   Sub-TLV   |                                       |
   +=============+=============+=======================================+
   |     BIER    | BIER Sub-TLV|[RFC8444],                             |
   | information |             |[I-D.ietf-bier-ospfv3-extensions]      |
   +-------------+-------------+---------------------------------------+
   |  BIER MPLS  |  BIER MPLS  |[RFC8444],                             |
   |Encapsulation|Encapsulation|[I-D.ietf-bier-ospfv3-extensions]      |
   |             |   Sub-TLV   |                                       |
   +-------------+-------------+---------------------------------------+
   |BIER non-MPLS|BIER non-MPLS|[I-D.ietf-bier-lsr-non-mpls-extensions]|
   |Encapsulation|Encapsulation|                                       |
   |             |   Sub-TLV   |                                       |
   +-------------+-------------+---------------------------------------+
                    Table 3: OSPFv2/OSPFV3 BIER TLVs/Sub-TLVs

5.  IANA Considerations

   IANA maintains a registry group called "Border Gateway Protocol -
   Link State (BGP-LS) Parameters" with a registry called "BGP-LS NLRI
   and Attribute TLVs".  The following TLV codepoints are suggested (for
   early allocation by IANA):

   +============+=============================+==================+
   | Code Point |         Description         | Value defined in |
   +============+=============================+==================+
   |    TBD1    |       BIER information      |  this document   |
   +------------+-----------------------------+------------------+
   |    TBD2    |   BIER MPLS Encapsulation   |  this document   |
   +------------+-----------------------------+------------------+
   |    TBD3    | BIER non-MPLS Encapsulation |  this document   |
   +------------+-----------------------------+------------------+
              Table 4: The new Prefix Attribute TLVs

6.  Security Considerations

   Procedures and protocol extensions defined in this document do not
   affect the BGP security model.  See the "Security
   Considerations"section of [RFC4271] for a discussion of BGP
   security.Security considerations for acquiring and distributing BGP-
   LS information are discussed in [RFC9552].

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   The TLVs introduced in this document are used to propagate the Bit
   Index Explicit Replication (BIER) defined in [RFC8401], [RFC8444] ,
   [I-D.ietf-bier-ospfv3-extensions], and
   [I-D.ietf-bier-lsr-non-mpls-extensions].  These TLVs represent the
   bier information associated with the prefix.  It is assumed that the
   IGP instances originating these TLVs will support all the required
   security and authentication mechanisms in [RFC8401], [RFC8444],
   [I-D.ietf-bier-ospfv3-extensions] ,and
   [I-D.ietf-bier-lsr-non-mpls-extensions] in order to prevent any
   security issues when propagating the TLVs into BGP-LS.  The
   advertisement of the link attribute information defined in this
   document present no additional risk beyond that associated with the
   existing link attribute informations already supported in [RFC9552].

7.  Acknowledgments

   The authors thank Peter Psenak, Ketan Talaulikar, Gyan Mishra and
   Benchong Xu and many others for their suggestions and comments.

8.  References

8.1.  Normative References

   [I-D.ietf-bier-lsr-non-mpls-extensions]
              Dhanaraj, S., Yan, G., Wijnands, I., Psenak, P., Zhang, Z.
              J., and J. Xie, "LSR Extensions for BIER non-MPLS
              Encapsulation", Work in Progress, Internet-Draft, draft-
              ietf-bier-lsr-non-mpls-extensions-04, 19 August 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-bier-
              lsr-non-mpls-extensions-04>.

   [I-D.ietf-bier-ospfv3-extensions]
              Psenak, P., Nainar, N. K., Wijnands, I., and Z. Zhang,
              "OSPFv3 Extensions for BIER", Work in Progress, Internet-
              Draft, draft-ietf-bier-ospfv3-extensions-08, 23 July 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-bier-
              ospfv3-extensions-08>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [RFC8296]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
              for Bit Index Explicit Replication (BIER) in MPLS and Non-
              MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
              2018, <https://www.rfc-editor.org/info/rfc8296>.

   [RFC8401]  Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z.
              Zhang, "Bit Index Explicit Replication (BIER) Support via
              IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018,
              <https://www.rfc-editor.org/info/rfc8401>.

   [RFC8444]  Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A.,
              Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2
              Extensions for Bit Index Explicit Replication (BIER)",
              RFC 8444, DOI 10.17487/RFC8444, November 2018,
              <https://www.rfc-editor.org/info/rfc8444>.

   [RFC8571]  Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
              C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
              IGP Traffic Engineering Performance Metric Extensions",
              RFC 8571, DOI 10.17487/RFC8571, March 2019,
              <https://www.rfc-editor.org/info/rfc8571>.

   [RFC9552]  Talaulikar, K., Ed., "Distribution of Link-State and
              Traffic Engineering Information Using BGP", RFC 9552,
              DOI 10.17487/RFC9552, December 2023,
              <https://www.rfc-editor.org/info/rfc9552>.

8.2.  Informative References

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

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   [RFC5376]  Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS
              Requirements for the Path Computation Element
              Communication Protocol (PCECP)", RFC 5376,
              DOI 10.17487/RFC5376, November 2008,
              <https://www.rfc-editor.org/info/rfc5376>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

Authors' Addresses

   Ran Chen
   ZTE Corporation
   Nanjing
   China
   Email: chen.ran@zte.com.cn

   Zheng Zhang
   ZTE Corporation
   Nanjing
   China
   Email: zhang.zheng@zte.com.cn

   Vengada Prasad Govindan
   Cisco
   Email: venggovi@cisco.com

   IJsbrand Wijnands
   Individual
   Email: ice@braindump.be

   Zhaohui Zhang
   Juniper Networks
   Email: zzhang@juniper.net

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