OSPFv3 Extensions for BIER
draft-ietf-bier-ospfv3-extensions-09

Bit Indexed Explicit Replication                               P. Psenak
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                          N. Nainar, Ed.
Expires: 25 July 2026                                             Oracle
                                                            IJ. Wijnands
                                                  Individual Contributor
                                                           Z. Zhang, Ed.
                                                         ZTE Corporation
                                                         21 January 2026

                       OSPFv3 Extensions for BIER
                  draft-ietf-bier-ospfv3-extensions-09

Abstract

   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.  The BIER architecture uses MPLS or other encapsulations to
   steer the multicast traffic towards the receivers.

   This document describes the OSPFv3 protocol extensions required for
   BIER with MPLS encapsulation.  Support for other encapsulation types
   is outside the scope of this document.

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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   This Internet-Draft will expire on 25 July 2026.

Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Flooding of BIER Information in OSPFv3  . . . . . . . . . . .   3
     2.1.  BIER Sub-TLV  . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  BIER MPLS Encapsulation Sub-TLV . . . . . . . . . . . . .   5
     2.3.  Flooding scope of BIER Information  . . . . . . . . . . .   7
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Bit Index Explicit Replication (BIER) [RFC8279] 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 explicitly require a
   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 bit-string in which each bit represents exactly one
   BFER to which the packet could be forwarded.  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.

   The BIER architecture requires routers participating in BIER to
   exchange BIER related information within a given domain.  The BIER
   architecture permits link-state routing protocols to perform
   distribution of such information.  [RFC8444] defines the OSPFv2
   protocol extensions to distribute BIER specific information.  This
   document describes extensions to OSPFv3 to enable it to advertise
   BIER specific information in the case where BIER uses MPLS
   encapsulation as described in [RFC8296].

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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.  Flooding of BIER Information in OSPFv3

   All BIER specific information that a Bit-Forwarding Router (BFR)
   needs to advertise to other BFRs is associated with a BFR-Prefix.  A
   BFR prefix is a unique (within a given BIER domain) routable IPv4 or
   IPv6 address that is assigned to each BFR as described in more detail
   in [RFC8279].

   [RFC8362] defines the format of TLV that allows additional
   information to be carried in OSPFv3 LSAs.  This section defines the
   required Sub-TLVs to carry BIER information that is associated with
   the BFR-Prefix.  The Sub-TLV defined in this section can be carried
   in the OSPFv3 Extended LSA TLVs [RFC8362] listed below:

      Inter-Area-Prefix TLV

      External-Prefix TLV

      Intra-Area-Prefix TLV

2.1.  BIER Sub-TLV

   A Sub-TLV of the above mentioned Prefix TLVs is defined for
   distributing BIER information.  The Sub-TLV is called the BIER Sub-
   TLV.  Multiple BIER Sub-TLVs may be included in any of the above
   mentioned Prefix TLV.

   The format is the same with the definition in [RFC8444]:

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      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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Sub-domain-ID |      MT-ID    |              BFR-id           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     BAR       |     IPA       |        Reserved               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sub-TLVs (variable)                      |
      +-                                                             -+
      |                                                               |

      Type: TBD1

      Length: The length in octets of the BIER Sub-TLV's value part.

      Sub-domain-ID: Unique value identifying the BIER sub-domain within
      the BIER domain, as described in [RFC8279]

      MT-ID: Multi-Topology ID (as defined in [RFC4915])that identifies
      the topology that is associated with the BIER sub-domain.

      BFR-id: A 2-octet field encoding the BFR-id, as documented in
      Section 2 of [RFC8279].  Typically, a BFR as an intermediate node
      only is not assigned a BFR-id, but still needs to announce and
      flood the BIER Sub-TLV and related MPLS encapsulation Sub-TLV for
      BIER BIFT construction.

      BAR: Single octet BIER specific algorithm used to calculate
      underlay paths to reach other BFRs.  Values are allocated from the
      "BIER Algorithm" registry which is defined in [RFC8401].

      IPA: Single octet IGP algorithm to either modify, enhance or
      replace the calculation of underlay paths to reach other BFRs as
      defined by the BAR value.  Values are defined in the "IGP
      Algorithm Types" registry in [RFC8665].

      Reserved: A 2-octet field, MUST be set to 0 on transmission and
      MUST be ignored by the receiver.

   Each BIER sub-domain MUST be associated with one and only one OSPF
   topology that is identified by the MT-ID.  If the association between
   BIER sub-domain and value of the MT-ID field advertised in the BIER
   Sub-TLV by other BFRs is in conflict with the association locally
   configured on the receiving router, the received BIER Sub-TLV MUST be
   ignored.

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   If the MT-ID value is outside of the values specified in [RFC4915],
   the BIER Sub-TLV MUST be ignored by the receiver.

   A Prefix-TLV can be used for multiple BIER sub-domains.  For each
   sub-domain indicated by Sub-domain-ID, there is only one BIER Sub-
   TLV.  If a BFR advertises the same Sub-domain-ID in multiple BIER
   Sub-TLVs, the BFR MUST be treated as if it did not advertise a BIER
   Sub-TLV for such sub-domain.

   All BFRs MUST detect advertisement of duplicate valid BFR-IDs for a
   given Sub-domain-ID.  When such duplication is detected by the BFR,
   it MUST behave as described in section 5 of [RFC8279].

   The supported BAR and IPA algorithms MUST be consistent for all
   routers supporting a given BFR sub-domain.  A router receiving BIER
   Sub-TLV advertisement with a value in BAR or IPA fields which does
   not match the locally configured value for a given BFR sub-domain,
   MUST report a misconfiguration for such BIER sub-domain and MUST
   ignore such BIER Sub-TLV.

   Implementations should set the BAR and IPA fields to zero by default.
   Other values may be carried in these fields, but the processing is
   outside the scope of this document.

   When the BIER Sub-TLV is ignored due to any of the reasons specified
   in this section, the flooding of the TLV is not affected.

2.2.  BIER MPLS Encapsulation Sub-TLV

   The BIER MPLS Encapsulation Sub-TLV is a Sub-TLV of the BIER Sub-TLV
   defined in Section 2.1.  The BIER MPLS Encapsulation Sub-TLV is used
   in order to advertise MPLS specific information used for BIER.  It
   MAY appear multiple times in the BIER Sub-TLV.

   The BIER MPLS Encapsulation Sub-TLV has the following format:

      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    |                    Label                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |BS Len |                     Reserved                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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      Type: Set to TBD2.

      Length: 8 octets

      Max SI: A 1-octet field encoding the maximum Set Identifier
      (section 1 of [RFC8279]), used in the encapsulation for this BIER
      sub-domain for the bitstring length indicated by the BS Len field.

      Label: A 3-octet field, where the 20 rightmost bits represent the
      first label in the label range.  The 4 leftmost bits MUST be
      ignored by the receiver.

      Bit String Length: A 4 bits field indicating the supported
      BitString length associated with this BFR-prefix using the
      exponential encoding defined in section 2.1.2 [RFC8296].  The set
      of values allowed in this field are specified in that section.

      Reserved: A 28 bits field, MUST be set to 0 on transmission and
      MUST be ignored by the receiver.

      The "label range" is the set of labels beginning with the Label
      and ending with (Label + (Max SI)).  A unique label range is
      allocated for each BitString length and Sub-domain-ID.  These
      labels are used for BIER forwarding as described in [RFC8279] and
      [RFC8296].

      The size of the label range is determined by the number of Set
      Identifiers (SI) (section 1 of [RFC8279]) that are used in the
      network.  Each SI maps to a single label in the label range.  The
      first label is for SI=0, the second label is for SI=1, etc.

   If the label associated with the Maximum Set Identifier exceeds the
   20 bit range, the BIER MPLS Encapsulation Sub-TLV MUST be ignored by
   the receiver.

   If the BS length is set to a value that does not match any of the
   allowed values specified in [RFC8296], the BIER MPLS Encapsulation
   Sub-TLV MUST be ignored.

   If same BS length is repeated in multiple BIER MPLS Encapsulation
   Sub-TLV inside the same BIER Sub-TLV, all MPLS encapsulation Sub-TLVs
   MUST be ignored by the receiver.

   Label ranges within all BIER MPLS Encapsulation Sub-TLVs advertised
   by the same BFR MUST NOT overlap.  If an overlap is detected, all
   BIER MPLS Encapsulation Sub-TLVs advertised by the BFR MUST be
   ignored by the receiver.

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   When the BIER Sub-TLV is ignored due to any of the reasons specified
   in this section, the flooding of the TLV is not affected..

2.3.  Flooding scope of BIER Information

   The flooding scope of the Extended LSAs [RFC8362] that is used for
   advertising the BIER Sub-TLV is area-local.  To allow BIER deployment
   in a multi-area environment, OSPFv3 must propagate BIER information
   between areas.

                    (  )         (  )         (  )
                  (      )     (      )     (      )
               R1  Area 1   R2  Area 0   R3  Area 2  R4
                  (      )     (      )     (      )
                    (  )         (  )         (  )

                  Figure 1: BIER propagation between areas

   The following procedure is used in order to propagate BIER related
   information between areas:

      When an OSPFv3 Area Border Router (ABR) advertises E-Inter-Area-
      Prefix-LSA from an intra-area or inter-area prefix to all its
      attached areas, it determines whether a BIER Sub-TLV should be
      included in this LSA.  To achieve this, an OSPFv3 ABR will:

      -  Examine its best path to the prefix in the source area and find
         the advertising router associated with the best path to that
         prefix.

      -  Determine if such advertising router advertised a BIER Sub-TLV
         for the prefix.  If yes, the ABR will copy the information from
         such BIER Sub-TLV when advertising BIER Sub-TLV to each
         attached area.

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      In the Figure 1, R1 advertises a prefix 2001:db8:b1e6::1/128 in
      Area 1.  It also includes BIER Sub-TLV in E-Intra-Area-Prefix-LSA.
      ABR R2 calculates the reachability for prefix
      2001:bdb8:b1e6::1/128 inside Area 1 and propagates it to Area 0
      using E-Inter-Area-Prefix-LSA.  When doing so, it copies the
      entire BIER Sub-TLV (including all its Sub-TLVs) it received from
      R1 in Area 1 and includes it in the E-Inter-Area-Prefix-LSA it
      generates for the prefix in Area 0.  ABR R3 calculates the
      reachability for prefix 2001:bdb8:b1e6::1/128 inside Area 0 and
      propagates it to Area 2.  When doing so, it copies the entire BIER
      Sub-TLV (including all its Sub-TLVs) it received from R2 in Area 0
      and includes it in E-Inter-Area-Prefix-LSA it generates for
      2001:bdb8:b1e6::1/128 in Area 2.

3.  Security Considerations

   This document introduces new Sub-TLVs for OSPFv3 Extended-LSAs.  It
   does not introduce any new security risks to OSPFv3.  Existing
   security concerns documented in [RFC8362] is applicable for the Sub-
   TLVs defined in this document.

   It is assumed that both BIER and OSPF layer is under a single
   administrative domain.  There can be deployments where potential
   attackers have access to one or more networks in the OSPFv3 routing
   domain.  In these deployments, stronger authentication mechanisms
   such as those specified in [RFC4552] SHOULD be used.

   The Security Considerations section of [RFC8279] discusses the
   possibility of performing a Denial of Service (DoS) attack by setting
   too many bits in the BitString of a BIER-encapsulated packet.
   However, this sort of DoS attack cannot be initiated by modifying the
   OSPF BIER advertisements specified in this document.  A BFIR decides
   which systems are to receive a BIER-encapsulated packet.  In making
   this decision, it is not influenced by the OSPF control messages.
   When creating the encapsulation, the BFIR sets one bit in the
   encapsulation for each destination system.  The information in the
   OSPF BIER advertisements is used to construct the forwarding tables
   that map each bit in the encapsulation into a set of next hops for
   the host that is identified by that bit, but is not used by the BFIR
   to decide which bits to set.  Hence an attack on the OSPF control
   plane cannot be used to cause this sort of DoS attack.

   While a BIER-encapsulated packet is traversing the network, a BFR
   that receives a BIER-encapsulated packet with n bits set in its
   BitString may have to replicate the packet and forward multiple
   copies.  However, a given bit will only be set in one copy of the
   packet.  That means that each transmitted replica of a received
   packet has fewer bits set (i.e., is targeted to fewer destinations)

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   than the received packet.  This is an essential property of the BIER
   forwarding process as defined in [RFC8279].  While a failure of this
   process might cause a DoS attack (as discussed in the Security
   Considerations of [RFC8279]), such a failure cannot be caused by an
   attack on the OSPF control plane.

   Implementations MUST assure that malformed TLV and Sub-TLV defined in
   this document are detected and do not provide a vulnerability for
   attackers to crash the OSPFv3 router or routing process.  Reception
   of malformed TLV or Sub-TLV SHOULD be counted and/or logged for
   further analysis.  Logging of malformed TLVs and Sub-TLVs SHOULD be
   rate-limited to prevent a Denial of Service (DoS) attack (distributed
   or otherwise) from overloading the OSPFv3 control plane.

4.  IANA Considerations

   The document requests two new allocations from the OSPFv3 Extended-
   LSA Sub-TLVs registry as defined in [RFC8362] with the range:
   4-32767.

      BIER Sub-TLV: TBD1

      BIER MPLS Encapsulation Sub-TLV: TBD2

5.  Acknowledgements

   The authors would like to thank Mankamana Mishra, Tony Przygienda,
   Huaimo Chen and Greg Shepherd for their review comments.

6.  Normative References

   [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>.

   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <https://www.rfc-editor.org/info/rfc4915>.

   [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>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

   [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>.

   [RFC8665]  Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
              H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", RFC 8665,
              DOI 10.17487/RFC8665, December 2019,
              <https://www.rfc-editor.org/info/rfc8665>.

Authors' Addresses

   Peter Psenak
   Cisco Systems, Inc.
   Apollo Business Center
   821 09 Mlynske nivy 43
   Slovakia
   Email: ppsenak@cisco.com

   Nagendra Kumar Nainar (editor)
   Oracle
   Research Triangle Park, NC 27709
   United States of America

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   Email: nagendrakumar.nainar@gmail.com

   IJsbrand Wijnands
   Individual Contributor
   1831 Diegem
   Belgium
   Email: ice@braindump.be

   Zheng Zhang (editor)
   ZTE Corporation
   China
   Email: zhang.zheng@zte.com.cn

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