BIER                                                            Z. Zhang
Internet-Draft                                           ZTE Corporation
Intended status: Standards Track                           Z. Zhang, Ed.
Expires: December 16, 2021                              Juniper Networks
                                                             I. Wijnands
                                                               M. Mishra
                                                           Cisco Systems
                                                              H. Bidgoli
                                                          G. Mishra, Ed.
                                                           June 14, 2021

               Supporting BIER in IPv6 Networks (BIERin6)


   BIER is a new architecture for the forwarding of multicast data
   packets without requiring per-flow state inside the network.  This
   document describes how the existing BIER encapsulation specified in
   RFC 8296 works in an IPv6 non-MPLS network, 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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any

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   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 December 16, 2021.

Copyright Notice

   Copyright (c) 2021 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
   ( 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified 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    3
   2.  IPv6 Header . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  IPv6 Options Considerations . . . . . . . . . . . . . . .   5
   3.  BIER Header . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  IPv6 Encapsulation Advertisement  . . . . . . . . . . . . . .   6
     4.1.  Format  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Inter-area prefix redistribution  . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   BIER [RFC8279] is a new architecture for the forwarding of multicast
   data packets.  It provides optimal forwarding through a "multicast
   domain" and it does not precondition construction of a multicast
   distribution tree, nor does it require intermediate nodes to maintain
   any per-flow state.

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   This document specifies non-MPLS BIER forwarding in an IPv6 [RFC8200]
   environment, referred to as BIERin6, using non-MPLS BIER
   encapsulation specified in [RFC8296].

   MPLS BIER forwarding in IPv6 is outside the scope of this document.

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

1.1.  BIER over L2/Tunnels

   [RFC8296] defines the BIER encapsulation format in MPLS and non-MPLS
   environment.  In case of non-MPLS environment, a BIER packet is the
   payload of an "outer" encapsulation, which has a "next header"
   codepoint that is set to a value that means "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 "non-MPLS 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:

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

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

1.2.  Considerations of Requirements for BIER in IPv6 Networks

   [draft-ietf-bier-ipv6-requirements] lists mandatory and optional
   requirements for BIER in IPv6 Networks.  As a solution based on the

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   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:

   o  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.

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

   Either way, the fragmentation/ESP is handled by a layer outside of
   BIER and then the resulting packets are treated as BIER payload.

   BIERin6 does support SRv6 based overlay services (e.g.  MVPN/EVPN).
   One of the following methods can be used (relevant overlay signaling
   will be specified separately):

   o  An ingress PE (which is a BFIR) can encapsulate customer packets
      with an IPv6 header (with optional fragmentation and ESP extension
      headers).  The destination address is a multicast locator plus the
      Fucn/Arg portion that identifies the service.  That IPv6 packet is
      then treated as BIER payload.  An egress PE (which is a BFER) uses
      the standard SRv6 procedures to forward the IPv6 packet that is
      exposed after the BIER header is decapsulated.

   o  Alternatively, since only the destination IPv6 address in the
      above-mentioned 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 IPv6 address (instead of an entire
      IPv6 header) is added between the BIER header and original

   BIERin6 being a solution based on [RFC8279] [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 (instead of using local 5-tuple input key to a
   hash function to locally generate the stateless 20-bit flow label) so
   that routers along the tunnel can do ECMP based on Flow Labels.  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 function, otherwise it

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   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:

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

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

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

   o  BIER Path Maximum Transmission Unit Discovery specified in

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

2.  IPv6 Header

   Whenever IPv6 encapsulation is used for BIER forwarding, 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
   IPv6 TTL MUST be set to 1.  Otherwise, 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.

2.1.  IPv6 Options Considerations

   For directly connected BIER routers, IPv6 Hop-by-Hop or Destination
   options are irrelevant and SHOULD NOT be inserted by BFIR on the
   BIERin6 packet.  In this case IPv6 header, Next Header field should
   be set to TBD.  Any IPv6 packet arriving on BFRs and BFERs, with
   multiple extension header where the last extension header has a Next

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   Header field set to TBD, SHOULD be discard and the node should
   transmit an ICMP Parameter Problem message to the source of the
   packet (BFIR) with an ICMP code value of TBD10 ('invalid options for

   This also indicates that for disjoint BIER routers using IPv6
   encapsulation, there SHOULD NOT be any IPv6 Hop-by-Hop or Destination
   options be present in a BIERin6 packet.  In this case, if additional
   traffic engineering is required, IPv6 tunneling (i.e.  BIERin6 over
   SRv6) can be implemented.

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-ethernet-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-ethernet-extensions] is needed.

   Otherwise, a node that requires IPv6 encapsulation MUST advertise the
   BIER IPv6 transportation 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.

   In presence of multiple encapsulation possibilities hop-by-hop it is
   a matter of local policy which encapsulation is imposed and the
   receiving router MUST accept all encapsulations that it advertised.

4.1.  Format

   The BIER IPv6 transportation is a new sub-sub-TLV of BIER Ethernet
   Encapsulation sub-TLV defined in OSPFv3, and a new sub-sub-sub-TLV of
   BIER Ethernet Encapsulation sub-sub-TLV defined in ISIS, 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      |

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   o  Type: For OSPF, value TBD1 (prefer 1) is used to indicate it is
      the IPv6 transportation sub-TLV.  For ISIS, value TBD2 (prefer 1)
      is used to indicate it is the IPv6 transportation sub-sub-TLV.

   o  Length: 0.

4.2.  Inter-area prefix redistribution

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

5.  IANA Considerations

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

   IANA is requested to assign a new "BIERin6" type for "invalid
   options" in the "ICMP code value" registry.

   IANA is requested to assign a new "BIER IPv6 transportation Sub-sub-
   TLV" type in the "OSPFv3 BIER Ethernet Encapsulation sub-TLV"

   IANA is requested to set up a new "BIER IPv6 transportation Sub-sub-
   sub-TLV" type in the "IS-IS BIER Ethernet Encapsulation sub-sub-TLV"

   IANA is requested to allocate a new value "IPv6 Address" from "BIER
   Next Protocol Identifiers" registry to indicate that an IPv6 address
   is inserted between the BIER header and BIER payload.

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

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8.1.  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,

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

   [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, <>.

   [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,

8.2.  Informative References

              Zhang, Z., Przygienda, A., Dolganow, A., Bidgoli, H.,
              Wijnands, I., and A. Gulko, "BIER Underlay Path
              Calculation Algorithm and Constraints", draft-ietf-bier-
              bar-ipa-07 (work in progress), September 2020.

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              Xiong, Q., Mirsky, G., Hu, F., and C. Liu, "BIER BFD",
              draft-ietf-bier-bfd-01 (work in progress), April 2021.

              Xu, X., Chen, M., Patel, K., Wijnands, I., and A.
              Przygienda, "BGP Extensions for BIER", draft-ietf-bier-
              idr-extensions-07 (work in progress), September 2019.

              McBride, M., Xie, J., Geng, X., Dhanaraj, S., Asati, R.,
              Zhu, Y., Mishra, G., and Z. Zhang, "BIER IPv6
              Requirements", draft-ietf-bier-ipv6-requirements-09 (work
              in progress), September 2020.

              Dhanaraj, S., Yan, G., Wijnands, I., Psenak, P., Zhang,
              Z., and J. Xie, "LSR Extensions for BIER over Ethernet",
              draft-ietf-bier-lsr-ethernet-extensions-02 (work in
              progress), December 2020.

              Wijnands, I., Mishra, M., Xu, X., and H. Bidgoli, "An
              Optional Encoding of the BIFT-id Field in the non-MPLS
              BIER Encapsulation", draft-ietf-bier-non-mpls-bift-
              encoding-03 (work in progress), November 2020.

              Psenak, P., Nainar, N. K., and I. Wijnands, "OSPFv3
              Extensions for BIER", draft-ietf-bier-ospfv3-extensions-03
              (work in progress), November 2020.

              Mirsky, G., Przygienda, T., and A. Dolganow, "Path Maximum
              Transmission Unit Discovery (PMTUD) for Bit Index Explicit
              Replication (BIER) Layer", draft-ietf-bier-path-mtu-
              discovery-10 (work in progress), March 2021.

              Kumar, N., Pignataro, C., Akiya, N., Zheng, L., Chen, M.,
              and G. Mirsky, "BIER Ping and Trace", draft-ietf-bier-
              ping-07 (work in progress), May 2020.

              Mirsky, G., Zheng, L., Chen, M., and G. Fioccola,
              "Performance Measurement (PM) with Marking Method in Bit
              Index Explicit Replication (BIER) Layer", draft-ietf-bier-
              pmmm-oam-10 (work in progress), March 2021.

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              Zhang, Z., Wu, B., Zhang, Z., Wijnands, I., and Y. Liu,
              "BIER Prefix Redistribute", draft-ietf-bier-prefix-
              redistribute-00 (work in progress), August 2020.

              Min, X., Zhang, Z., Liu, Y., Nainar, N. K., and C.
              Pignataro, "Bit Index Explicit Replication (BIER)
              Encapsulation for In-situ OAM (IOAM) Data", draft-xzlnp-
              bier-ioam-01 (work in progress), January 2021.

              Zhang, Z. and T. Przygienda, "BIER in BABEL", draft-zhang-
              bier-babel-extensions-04 (work in progress), November

              Zhang, Z., Bonica, R., and K. Kompella, "Generic Transport
              Functions", draft-zzhang-tsvwg-generic-transport-
              functions-00 (work in progress), November 2020.

   [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


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   Mankamana Mishra
   Cisco Systems


   Hooman Bidgoli


   Gyan Mishra (editor)


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