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Supporting BIER in IPv6 Networks (BIERin6)

Document Type Active Internet-Draft (bier WG)
Authors Zheng Zhang , Zhaohui (Jeffrey) Zhang , IJsbrand Wijnands , Mankamana Prasad Mishra , Hooman Bidgoli , Gyan Mishra
Last updated 2023-09-18
Replaces draft-zhang-bier-bierin6
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state WG Document
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IESG IESG state I-D Exists
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BIER                                                            Z. Zhang
Internet-Draft                                           ZTE Corporation
Intended status: Standards Track                           Z. Zhang, Ed.
Expires: 21 March 2024                                  Juniper Networks
                                                             I. Wijnands
                                                               M. Mishra
                                                           Cisco Systems
                                                              H. Bidgoli
                                                               G. Mishra
                                                       18 September 2023

               Supporting BIER in IPv6 Networks (BIERin6)


   BIER is a multicast forwarding architecture that does not require
   per-flow state inside the network yet still provides optimal
   replication.  This document describes how the existing BIER
   encapsulation specified in RFC 8296 works in a non-MPLS IPv6 network,
   which is referred to as BIERin6.  Specifically, like in an IPv4
   network, BIER can work over L2 links directly or over tunnels.  In
   case of IPv6 tunneling, a new IP "Next Header" type is to be assigned
   for BIER.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 21 March 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  BIER over L2/Tunnels  . . . . . . . . . . . . . . . . . .   3
     1.2.  Considerations of Requirements for BIER in IPv6
           Networks  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  IPv6 Header . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  BIER Header . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  IPv6 Encapsulation Advertisement  . . . . . . . . . . . . . .   6
     4.1.  Format  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Inter-area prefix redistribution  . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   BIER [RFC8279] is a multicast forwarding architecture that does not
   require per-flow state inside the network yet still provides optimal

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   BIER forwarding with MPLS is IPv4/IPv6 agnostic.  This document
   describes how BIER works in a non-MPLS IPv6 [RFC8200] environment
   using non-MPLS BIER encapsulation [RFC8296], with optional procedures
   specified for IPv6 specific features.

   This document uses terminology defined in [RFC8279] and [RFC8296].

1.1.  BIER over L2/Tunnels

   [RFC8296] defines the BIER encapsulation format for MPLS and non-MPLS
   data planes.  With a non-MPLS data plane, a BIER packet is the
   payload of an "outer" encapsulation, which could be a L2 link or a
   tunnel.  The outer encapsulation has a "next header" field that is
   set to a value for "non-MPLS BIER".  This "BIER over L2/Tunnel" model
   can be used as is in an IPv6 non-mpls environment, and is referred to
   as BIERin6.

   If a BFR needs to tunnel BIER packets to another BFR, e.g. per
   [RFC8279] Section 6.9, while any type of tunnel will work, for best
   efficiency native IPv6 encapsulation can be used with the destination
   address being the downstream BFR and the Next Header field set to a
   to-be-assigned value for BIER.

                          |  IPv6 header  | BIER header + data
                          |               |
                          | Next Header = |
                          |    BIER       |

   Between two directly connected BFRs, a BIER header can directly
   follow link layer header, e.g., an Ethernet header (with the
   Ethertype set to 0xAB37).  Optionally, IPv6 encapsulation can be used
   even between directly connected BFRs (i.e. one-hop IPv6 tunneling) in
   the following two cases:

   *  An operator mandates all traffic to be carried in IPv6.

   *  A BFR does not have BIER support in its "fast forwarding path" and
      relies on "slow/software forwarding path", e.g. in IPv6 Home
      Networking [RFC7368] where high throughput multicast forwarding
      performance is not critical.

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1.2.  Considerations of Requirements for BIER in IPv6 Networks

   [I-D.ietf-bier-ipv6-requirements] lists mandatory and optional
   requirements for BIER in IPv6 Networks.  As a solution based on the
   BIER over L2/tunnel model [RFC8296], BIERin6 satisfies all the
   mandatory requirements.

   For the two optional requirements for fragmentation and Encapsulating
   Security Payload (ESP), they can be satisfied by one of two ways:

   *  IPv6 based fragmentation/ESP: a BFIR encapsulates the payload in
      IPv6 with fragmentation and/or ESP header, and then the IPv6
      packets are treated as BIER payload.

   *  Generic Fragmentation/ESP
      [I-D.zzhang-intarea-generic-delivery-functions]: a BFIR does
      generic fragmentation and/or ESP (without using IPv6
      encapsulation) and the resulting packets are treated as BIER

   BIERin6 can support SRv6 based overlay services (e.g.  MVPN/EVPN)
   with one of the following methods:

   *  An ingress PE (which is a BFIR) can encapsulate customer packets
      with an IPv6 header (with optional fragmentation and ESP extension
      headers).  Any SRv6-based scheme can by used for service

   *  Alternatively, since only the IPv6 address in the above-mentioned
      outer IPv6 header is used for service delimiting purpose, a new
      value can be assigned for the Proto field in the BIER header to
      indicate that an SRv6 Service SID [RFC9252] (instead of an entire
      IPv6 header) is added between the BIER header and original
      payload.  For example, an End.DT2/4/6 service SID could be used to
      route the original payload in a corresponding VRF.

   The details of fagmentation/ESP support and service delimitation are
   all outside the scope of this document.

   BIERin6 being a solution based on [RFC8279] and [RFC8296], ECMP is
   inherently supported by BFRs using the the 20-bit entropy field in
   the BIER header for the load balancing hash.  When a BIER packet is
   transported over an IPv6 tunnel, the entropy value is copied into the
   20-bit IPv6 Flow Label [RFC6437], so that routers along the tunnel
   can do ECMP based on Flow Labels (instead of hashing based on 5-tuple
   of an IP packet).  For a router along the tunnel doing deep packet
   inspection for ECMP purpose, if it understands BIER header it can go
   past the BIER header to look for the 5-tuple input key to a hash

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   function.  Otherwise, it stops at the BIER header.  In either case
   the router will not mistake the BIER header as an IP header so no
   misordering should happen.

   BIER has its own OAM functions independent of those related to the
   underlying links or tunnels.  With BIERin6 following the "BIER over
   L2/tunnel" model, IPv6 OAM function and BIER OAM functions are used
   independently for their own purposes.

   Specifically, BIERin6 works with all of the following OAM methods, or
   any future methods that are based on the "BIER over L2/tunnel" model:

   *  BIER OAM specified in [I-D.ietf-bier-ping]

   *  BIER BFD specified in [I-D.ietf-bier-bfd]

   *  BIER Performance Measurement specified in [I-D.ietf-bier-pmmm-oam]

   *  BIER Path Maximum Transmission Unit Discovery specified in

   *  BIER IOAM specified in [I-D.xzlnp-bier-ioam]

2.  IPv6 Header

   If IPv6 encapsulation is used to tunnel BIER packets (whether to a
   direct or indirect BIER neighbor), the Next Header field in the IPv6
   Header (if there are no extension headers), or the Next Header field
   in the last extension header is set to TBD, indicating that the
   payload is a BIER packet.

   If the neighbor is directly connected, The destination address in
   IPv6 header SHOULD be the neighbor's link-local address on this
   router's outgoing interface.  The source destination address SHOULD
   be this router's link-local address on the outgoing interface, and
   the TTL MUST be set to 1.

   If the neighbor is not directly connected, the destination address
   SHOULD be the BIER prefix of the BFR neighbor.  The source address
   SHOULD be this router's BIER prefix, and the TTL MUST be large enough
   to get the packet to the BFR neighbor.

   The "Flow label" field in the IPv6 packet SHOULD be copied from the
   entropy field in the BIER encapsulation.

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3.  BIER Header

   The BIER header MUST be encoded per Section 2.2 of [RFC8296].

   The BIFT-id is either encoded per
   [I-D.ietf-bier-non-mpls-bift-encoding] or per advertised by BFRs, as
   specified in [I-D.ietf-bier-lsr-non-mpls-extensions].

4.  IPv6 Encapsulation Advertisement

   When IPv6 encapsulation is not required between directly connected
   BFRs, no signaling in addition to that specified in
   [I-D.ietf-bier-lsr-non-mpls-extensions] is needed.

   Otherwise, a node that requires IPv6 encapsulation MUST advertise the
   BIER IPv6 encapsulation sub-sub-sub-TLV/sub-sub-TLV according to
   local configuration or policy in the BIER domain to request other
   BFRs to always use IPv6 encapsulation.

4.1.  Format

   The BIER IPv6 Encapsulation is a new sub-sub-TLV of OSPFv3 BIER non-
   MPLS Encapsulation sub-TLV, and a new sub-sub-sub-TLV of ISIS BIER
   non-MPLS Encapsulation sub-sub-TLV as per

       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      |

   *  Type: For OSPF, value TBD1 indicates it is the IPv6 Encapsulation
      sub-TLV.  For ISIS, value TBD2 indicates it is the IPv6
      encapsulation sub-sub-TLV.

   *  Length: 0.

4.2.  Inter-area prefix redistribution

   When BFR-prefixes are advertised across IGP areas per
   [I-D.ietf-bier-lsr-non-mpls-extensions] or redistributed across
   protocol boundaries per [I-D.ietf-bier-prefix-redistribute], the BIER
   IPv6 encapsulation sub-sub-TLV or sub-sub-sub-TLV MAY be re-
   advertised/re-distributed as well.

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5.  IANA Considerations

   IANA is requested to assign a "BIER" type for "Next Header" in the
   "Assigned Internet Protocol Numbers" registry.

   IANA is requested to assign a "BIER IPv6 encapsulation Sub-sub-TLV"
   type in the "OSPFv3 BIER non-MPLS Encapsulation sub-TLV" Registry.

   IANA is requested to assign a "BIER IPv6 encapsulation Sub-sub-sub-
   TLV" type in the "IS-IS BIER non-MPLS Encapsulation sub-sub-TLV"

   IANA is requested to allocate a value "SRv6 Service" from "BIER Next
   Protocol Identifiers" registry to indicate that BIER payload starts
   with an SRv6 Service SID.

6.  Security Considerations

   General IPv6 and BIER security considerations apply.

7.  Acknowledgement

   The authors would like to thank Tony Przygienda, Nagendra Kumar for
   their review and valuable comments.

8.  References

8.1.  Normative References

              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-01, 19 September 2022,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,

   [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,

   [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, <>.

   [RFC9252]  Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
              B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
              Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
              DOI 10.17487/RFC9252, July 2022,

8.2.  Informative References

              Xiong, Q., Mirsky, G., hu, F., and C. Liu, "BIER BFD",
              Work in Progress, Internet-Draft, draft-ietf-bier-bfd-04,
              11 September 2023, <

              McBride, M., Xie, J., Geng, X., Dhanaraj, S., Asati, R.,
              Zhu, Y., Mishra, G. S., and Z. J. Zhang, "BIER IPv6
              Requirements", Work in Progress, Internet-Draft, draft-
              ietf-bier-ipv6-requirements-09, 28 September 2020,

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              Wijnands, I., Mishra, M. P., Xu, X., and H. Bidgoli, "An
              Optional Encoding of the BIFT-id Field in the non-MPLS
              BIER Encapsulation", Work in Progress, Internet-Draft,
              draft-ietf-bier-non-mpls-bift-encoding-04, 30 May 2021,

              Mirsky, G., Przygienda, T., and A. Dolganow, "Path Maximum
              Transmission Unit Discovery (PMTUD) for Bit Index Explicit
              Replication (BIER) Layer", Work in Progress, Internet-
              Draft, draft-ietf-bier-path-mtu-discovery-14, 26 March
              2023, <

              Nainar, N. K., Pignataro, C., Chen, M., and G. Mirsky,
              "BIER Ping and Trace", Work in Progress, Internet-Draft,
              draft-ietf-bier-ping-12, 29 July 2023,

              Mirsky, G., Zheng, L., Chen, M., and G. Fioccola,
              "Performance Measurement (PM) with Marking Method in Bit
              Index Explicit Replication (BIER) Layer", Work in
              Progress, Internet-Draft, draft-ietf-bier-pmmm-oam-14, 10
              July 2023, <

              Zhang, Z., Wu, B., Zhang, Z. J., Wijnands, I., Liu, Y.,
              and H. Bidgoli, "BIER Prefix Redistribute", Work in
              Progress, Internet-Draft, draft-ietf-bier-prefix-
              redistribute-05, 7 September 2023,

              Min, X., Zhang, Z., Liu, Y., Nainar, N. K., and C.
              Pignataro, "BIER Encapsulation for IOAM Data", Work in
              Progress, Internet-Draft, draft-xzlnp-bier-ioam-06, 31
              July 2023, <

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              Zhang, Z. J., Bonica, R., Kompella, K., and G. Mirsky,
              "Generic Delivery Functions", Work in Progress, Internet-
              Draft, draft-zzhang-intarea-generic-delivery-functions-03,
              11 July 2022, <

   [RFC7368]  Chown, T., Ed., Arkko, J., Brandt, A., Troan, O., and J.
              Weil, "IPv6 Home Networking Architecture Principles",
              RFC 7368, DOI 10.17487/RFC7368, October 2014,

Authors' Addresses

   Zheng(Sandy) Zhang
   ZTE Corporation

   Zhaohui Zhang (editor)
   Juniper Networks

   IJsbrand Wijnands

   Mankamana Mishra
   Cisco Systems

   Hooman Bidgoli

   Gyan Mishra

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