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Versions: (draft-xie-bier-6man-encapsulation) 00 01 02 03

Network Working Group                                             J. Xie
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                                 L. Geng
Expires: January 21, 2020                                   China Mobile
                                                              M. McBride
                                                               Futurewei
                                                                R. Asati
                                                                   Cisco
                                                             S. Dhanaraj
                                                                  Huawei
                                                           July 20, 2019


            Encapsulation for BIER in Non-MPLS IPv6 Networks
                  draft-xie-bier-ipv6-encapsulation-03

Abstract

   This document proposes a BIER IPv6 (BIERv6) encapsulation for Non-
   MPLS IPv6 Networks using the IPv6 Destination Option extension
   header.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] and
   [RFC8174].

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 https://datatracker.ietf.org/drafts/current/.

   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 January 21, 2020.






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Copyright Notice

   Copyright (c) 2019 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
   (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 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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  BIER IPv6 Encapsulation . . . . . . . . . . . . . . . . . . .   3
     3.1.  BIER Option in IPv6 Destination Options Header  . . . . .   3
     3.2.  Multicast and Unicast Destination Address . . . . . . . .   6
     3.3.  BIERv6 Packet Format  . . . . . . . . . . . . . . . . . .   8
   4.  BIERv6 Packet Processing  . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  BIER Option Type  . . . . . . . . . . . . . . . . . . . .  11
     6.2.  End.BIER Function . . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Bit Index Explicit Replication (BIER) [RFC8279] is an architecture
   that provides optimal multicast forwarding without requiring
   intermediate routers to maintain any per-flow state by using a
   multicast-specific BIER header.

   [RFC8296] defines a common BIER Header format for MPLS and Non-MPLS
   networks.  It has defined two types of encapsulation methods using
   the common BIER Header, (1) BIER encapsulation in MPLS networks,
   here-in after referred as MPLS BIER Header in this document and (2)
   BIER encapsulation in Non-MPLS networks, here-in after referred as
   Non-MPLS BIER Header in this document.  [RFC8296] also assigned



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   Ethertype=0xAB37 for Non-MPLS BIER Header packets to be directly
   carried over the Ethernet links.

   This document proposes a BIER IPv6 encapsulation for Non-MPLS IPv6
   Networks, defining a method to carry the standard Non-MPLS BIER
   header (as defined in [RFC8296]) in the native IPv6 header.  A new
   IPv6 Option type - BIER Option is defined to encode the standard Non-
   MPLS BIER header and this newly defined BIER Option is carried under
   the Destination Options header of the native IPv6 Header [RFC8200].

   This document details one of the proposed solutions for transporting
   BIER packets in an IPv6 network.  To better understand the overall
   BIER IPv6 problem space, use cases and proposed solutions, refer to
   [I-D.ietf-bier-ipv6-requirements].

2.  Terminology

   Readers of this document are assumed to be familiar with the
   terminology and concepts of the documents listed as Normative
   References.

   The following new terms are used throughout this document:

   o  BIERv6 - BIER IPv6.

   o  BIER Option - An Option type carried in IPv6 Destination Options
      Header which includes the standard Non-MPLS BIER Header.

   o  BIERv6 Header - An IPv6 Header with BIER Option.

   o  BIERv6 Packet - An IPv6 packet with BIERv6 Header.  Such an IPv6
      packet typically carries the user multicast payload and is
      forwarded by BFRs in the BIERv6 network towards the multicast
      receivers.

3.  BIER IPv6 Encapsulation

3.1.  BIER Option in IPv6 Destination Options Header

   Destination Options Header and the Options that can be carried under
   this extension header is defined in [RFC8200].  This document defines
   a new Option type - BIER Option, to encode the Non-MPLS BIER header.
   As specified in Section 4.2 [RFC8200], the BIER Option follows type-
   length-value (TLV) encoding format and the standard Non-MPLS BIER
   header [RFC8296] is encoded in the value portion of the BIER Option
   TLV.





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   This BIER Option MUST be carried only inside the IPv6 Destination
   Options header and MUST NOT be carried under the Hop-by-Hop Options
   header.

   Co-existence of Destination Options Header with BIER option TLV and
   other IPv6 extension headers MUST confirm to the general requirements
   defined in [RFC8200].  In addition to the requirements defined in
   [RFC8200], this document requires that the Destination Options Header
   with a BIER Option TLV MUST appear only after the Routing Header if
   the Routing Header is present in the IPv6 Header.

   The BIER Option is encoded in type-length-value (TLV) format as
   follows:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Next Header  |  Hdr Ext Len  |  Option Type  | Option Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~          Non-MPLS BIER Header (defined in RFC8296)            ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Next Header  8-bit selector.  Identifies the type of header
      immediately following the Destination Options header.

   Hdr Ext Len  8-bit unsigned integer.  Length of the Destination
      Options header in 8-octet units, not including the first 8 octets.

   Option Type  To be allocated by IANA.  See section 6.

   Option Length  8-bit unsigned integer.  Length of the option, in
      octets, excluding the Option Type and Option Length fields.

   Non-MPLS BIER Header  The Non-MPLS BIER Header defined in RFC8296.
      Fields in the Non-MPLS BIER Header MUST be encoded as below.



        BIFT-id: The BIFT-id is a domain-wide unique value in Non-MPLS
        IPv6 encapsulation.  See Section 2.2 of RFC 8296.

        TC: SHOULD be set to binary value 000 upon transmission and MUST
        be ignored upon.  See Section 2.2 of RFC 8296.

        S bit: SHOULD be set to 1 upon transmission, and MUST be ignored
        upon reception.  See Section 2.2 of RFC 8296.



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        TTL: MUST be set to 0 upon transmission, and MUST be ignored
        upon reception.  The function of TTL is replaced by the Hop
        Limit field in IPv6 header.

        Nibble: SHOULD be set to 0000 upon transmission, and MUST be
        ignored upon reception.  See Section 2.2 of RFC 8296.

        Ver: MUST be set to 0 upon transmission, and MUST be discarded
        when it is not 0 upon reception.  See Section 2.2 of RFC 8296.

        BSL: See Section 2.1.2 of RFC 8296.

        Entropy: See Section 2.1.2 of RFC 8296.

        OAM: See Section 2.1.2 of RFC 8296.

        Rsv: See Section 2.1.2 of RFC 8296.

        DSCP: SHOULD be set to binary value 000000 upon transmission and
        MUST be ignored upon reception.  In IPv6 BIER encapsulation,
        uses highest 6-bit of Traffic Class field of IPv6 header to hold
        a Differentiated Services Codepoint [RFC2474].

        Proto: SHOULD be set to 0 upon transmission and MUST be ignored
        upon reception.  In IPv6 BIER encapsulation, the functionality
        of this 6-bit Proto field is replaced by the Next Header field
        in Destination Options header, which is the last IPv6 extension
        header, to indicate the BIER payload, which is also IPv6
        payload.



           For BIER Proto 1, indicating a Downstream-assigned MPLS
           payload, use Next Header value 137.

           For BIER Proto 2, indicating an Upstream-assigned MPLS
           payload, there is no Next Header code currently.  An
           upstream-assigned MPLS label within the context of special
           BFIR router, which in turn is represented by the BFIR-id and
           the Sub-domain indirectly indicated by the BIFT-id in a BIER-
           MPLS or BIER-ETH packet, can be replaced by an IPv6 source
           address in a BIER IPv6 encapsulation packet in a direct
           manner.  In this case, use Next Header value 4 for IPv4
           payload, or value 41 for IPv6 payload.

           For BIER Proto 3, indicating an Ethernet payload, use Next
           Header value 97.




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           For BIER Proto 4, indicating an IPv4 payload, use Next Header
           value 4.

           For BIER Proto 5, indicating a BIER-OAM payload, use Next
           Header value 58.  How the BIER-PING is supported with BIER
           IPv6 encapsulation is outside the scope of this document.

           For BIER Proto 6, indicating an IPv6 payload, use Next Header
           value 41.

        BFIR-id: See Section 2.1.2 of RFC 8296.

        BitString: See Section 2.1.2 of RFC 8296.

3.2.  Multicast and Unicast Destination Address

   BIER is generally a hop-by-hop and one-to-many architecture, and thus
   the IPv6 Destination Address (DA) being a Multicast Address is a way
   one may think of as an approach for both the two paradigms in BIERv6
   encapsulation.

   However using a unicast address has the following benefits:

   1.  Tunneling a BIERv6 packet over a non-BIER capable router.

   2.  Fast rerouting a BIERv6 packet using a unicast by-pass tunnel.

   3.  Forwarding a BIERv6 packet to one of the many BFR neighbors
       connected on a LAN.

   4.  Connecting BIER domains, for example Data Center domains, in an
       overlay manner.

   Some of the above functions are assumed very basic requirements and
   part of BIER architecture as described in [RFC8279].  This document
   uses unicast address for both one-hop replication and multi-hop
   replication.

   The unicast address used in BIERv6 packet targeting a BFR SHOULD be
   the IPv6 BFR-Prefix advertised from this BFR.  When a BFR advertises
   the BIER information with BIERv6 encapsulation capability, the IPv6
   BFR-prefix of this BFR MUST be selected specifically for BIERv6
   packet forwarding.  Locally this "BIER Specific" IPv6 address is
   initialized in FIB with a flag of "BIER specific handling",
   represented as End.BIER function.  For convenience, the indication in
   FIB share the same space as SRv6 Endpoints Behaviors defined in
   [I-D.ietf-spring-srv6-network-programming].  Apart from this sharing




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   of code space, there is nothing dependent on SRv6.  The co-existance
   of BIERv6 and SRv6 is outside the scope of this document.

   BFR Prefix is used only in control plane in BIER MPLS encapsulation
   but not used in data plane.  While in BIERv6, BFR prefix is used in
   both control plane and data plane.  For the convinence of migration
   to BIERv6, it is RECOMMENDED to use an "exclusive" IPv6 address as
   BFR prefix when deploying BIER-MPLS in IPv6 networks.  The
   "exclusive" IPv6 address should not be used for general purpose like
   BGP session establishment, but for "BIER specific" function.  For
   Non-BIER IPv6 routers, the IPv6 address is a regular IPv6 prefix
   reachable through IPv6 unicast routing.

   The following is an example of configuring a BIER specific IPv6
   address and using this address as BFR prefix:

    # Config a BIER specific IPv6 address with 128-bit mask on loopback0.
    interface loopback0
      ipv6 address 2001:DB8::AB37 128 End.BIER

    # Config the BIER-specific IPv6 address on loopback0 as BFR Prefix.
    bier sub-domain 6 ipv6-underlay
      bfr-prefix interface loopback0

   The address used as "BIER specific" IPv6 address can be from inside
   the scope of an SRv6 Locator or outside the scope of the SRv6
   Locator(s) since it is a host prefix (128-bit prefix-length prefix).

   Each "BIER specific" address can be used in one or many sub-domains
   as BFR-prefix, such that it can be associated with one or many Multi-
   Topologies (MTs) or algorithms.

   More than one "BIER specific" address are also allowed as different
   BFR-prefix of more than one sub-domain, as described in section 2 of
   [RFC8279].

   The following is an example pseudo-code of the End.BIER function:

     1. IF NH = 60 and HopLimit > 0                               ;;Ref1
     2.   IF (OptType1 = BIER) and (OptLength1 = HdrExtLen*8 + 4) ;;Ref2
     3.     Lookup the BIER Header inside the BIER option TLV.
     4.     Forward via the matched entry.
     5.   ELSE                                                    ;;Ref3
     6.     Drop the packet and end the process.
     7. ELSE IF NH=ICMPv6 or (NH=60 and Dest_NH=ICMPv6)           ;;Ref4
     8.   Send to CPU.
     9. ELSE                                                      ;;Ref5
    10.   Drop the packet.



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   Ref1: Destination options header follows the IPv6 header directly and
   HopLimit is bigger than zero.

   Ref2: The first TLV is BIER type and is the only TLV present in
   Destination options header.

   Ref3/Ref5: Undesired packet is droped because the destination address
   is the BIER specific IPv6 address (End.BIER function).

   Ref4: An ICMPv6 packet using End.BIER as destination address.

3.3.  BIERv6 Packet Format

   As a multicast packet enters the BIER domain in a Non-MPLS IPv6
   network, the multicast packet will be encapsulated with BIERv6
   Header.

   Typically a BIERv6 header would contain the Destination Options
   Header as the only Extensions Header besides IPv6 Header.  However,
   it is allowed and possible for other extension headers to appear
   along with the Destination Options Header as long as the requirements
   listed in section 3.1 of this document is met.

   Format of the multicast packet with BIERv6 encapsulation carrying
   only the Destination Options header is depicted in the below figure.

      +---------------+--------------+------------
      | IPv6 header   | Dest Options | X type of
      |               | Header with  | multicast
      |               | BIER Option  | packet
      |               |              |
      | Next Hdr = 60 |  Nxt Hdr = X |
      +---------------+--------------+------------

   Format of the multicast packet with BIERv6 encapsulation carrying
   other extension headers along with Destination Options extension
   header is required to follow general recommendations of [RFC8200] and
   examples in other RFCs.  [RFC6275] introduces how the order should be
   when other extension headers carries along with Home address option
   in a destination options header.  Similar to this example, this
   document requires the Destination Options Header carrying the BIER
   option MUST be placed as follows:

   o  After the routing header, if that header is present

   o  Before the Fragment Header, if that header is present





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   o  Before the AH Header or ESP Header, if either one of those headers
      is present

   Source Address field in the IPv6 header MUST be a routable IPv6
   unicast address of the BFIR in any case.

   BFIR encodes the Non-MPLS BIER header in the above mentioned
   encapsulation format and forwards the BIERv6 packet to the nexthop
   BFR following the local BIFT table.

   BFRs in the IPv6 network, processes and replicates the packets
   towards the BFERs using the local BIFT table.  The bit-string field
   in the Non-MPLS BIER header may be changed by the BFRs as they
   replicate the packet.  BFRs MUST follow the procedures defined in
   section 3.1 as they modify the other fields in the Non-MPLS BIER
   header.  The source address in the IPv6 header MUST NOT be modified
   by the BFRs.

4.  BIERv6 Packet Processing

   There is no BIER-specific processing, and all the 8 steps in section
   6.5 of RFC8279 apply to BIERv6 packet processing.  However, there are
   some IPv6-specific processing procedures due to the base and general
   procedures of IPv6.

   On the overlay layer, when a multicast packet enters the BIER domain
   in a Non-MPLS IPv6 network, the Ingress BFR (BFIR) encapsulates the
   multicast packet with a BIERv6 Header, transforming it to a BIERv6
   packet.  The BIERv6 header includes an IPv6 header and IPv6
   Destination Options Header within a standard Non-MPLS BIER header.
   Source Address field in the IPv6 header MUST be set to a routable
   IPv6 unicast address of the BFIR.  Destination Address field in the
   IPv6 header is set to the BFR prefix of the next-hop BFR the BIERv6
   packet replicating to, no matter next-hop BFR is directly connected
   (one-hop) or not directly connected (multi-hop).

   On the BIER layer, upon receiving an BIERv6 packet, the BFR processes
   the IPv6 header first.  This is the general procedure of IPv6.

   If the IPv6 Destination address is an IPv6 BFR-Prefix unicast address
   of this BFR, a 'BIER Specific Handling' indication will be obtained
   by the preceding Unicast DA lookup (FIB lookup).  The BIER option, if
   exists, will be checked to decide which neighbor(s) to replicate the
   BIERv6 packet to.

   It is a local behavior to handle the combination of extension
   headers, options and the BIER option(s) in destination options header
   when a 'BIER Specific Handling' indication is got by the preceding



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   FIB lookup.  Early deployment of BIERv6 may require there is only one
   BIER option TLV in the destination options header followed the IPv6
   header.  How other extension headers or more BIER option TLVs in a
   BIERv6 packet is handled is outside the scope of this document.

   A packet having a 'BIER Specific Handling' indication but not having
   a BIER option is supposed to be a wrong packet or an ICMPv6 packet,
   and the process can be refered to the example in section 3.2.

   A packet not having a 'BIER Specific Handling' indication but having
   a BIER option SHOULD be processed normally as unicast forwarding
   procedures, which may be a behavior of drop, or send to CPU, or other
   behaviors in existing implementations.

   The Destination Address field in the IPv6 Header MUST change to the
   nexthop BFR's BFR Prefix if Unicast address is used in BIERv6.

   The Hop Limit field of IPv6 header MUST decrease by 1 when sending
   packets to a BFR neighbor, while the TTL in the BIER header MUST be
   unchanged.

   The BitString in the BIER header in the Destination Options Header
   may change when sending packets to a neighbor.  Such change of
   BitString MUST be aligned with the procedure defined in RFC8279.
   Because of the requirement to change the content of the option when
   forwarding BIERv6 packet, the BIER option type should have chg flag 1
   per section 4.2 of RFC8200.

   The procedures applies normally if a bit corresponding to the self
   bfr-id is set in the bit-string field of the Non-MPLS BIER header of
   the BIERv6 packet.  The node is considered to be an Egress BFR (BFER)
   in this case.  The BFER removes the BIERv6 header, including the IPv6
   header and the Destination Options header, and copies the packet to
   the multicast flow overlay.  The egress VRF of a packet may be
   determined by a further lookup on the IPv6 source address instead of
   the upstream-assigned MPLS Label as described in [RFC8556].

   The Fragment Header, AH Header or ESP Header, if exists after the
   BIER options header, can be processed on BFER only as part of the
   multicast flow overlay process.

5.  Security Considerations

   A BIERv6 packet with a special IPv6 Destination Address, the BFR
   prefix functioning as End.BIER, would be processed by BIER forwarding
   procedure only when the 'BIER Specific Handling' flag has been
   obtained ahead in the FIB lookup of the IPv6 header.  Otherwise the
   packet with an IPv6 BIER Option will not be processed by the



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   procedure but be processed as normal IPv6 packet.  A possible way of
   handling IPv6 packets with extension may be send to CPU for slow path
   processing.

6.  IANA Considerations

6.1.  BIER Option Type

   Allocation is expected from IANA for a BIER Option Type codepoint
   from the "Destination Options and Hop-by-Hop Options" sub-registry of
   the "Internet Protocol Version 6 (IPv6) Parameters" registry.  The
   value 0x70 is suggested.

           +-----------+-----+-----+-------+-------------+------------+
           | Hex Value | act | chg |  rest | Description | Reference  |
           +-----------+-----+-----+-------+-------------+------------+
           |    0x70   |  01 |  1  | 10000 | BIER Option | This draft |
           +-----------+-----+-----+-------+-------------+------------+

6.2.  End.BIER Function

   Allocation is expected from IANA for an End.BIER function codepoint
   from the "SRv6 Endpoint Behaviors" sub-registry.  The value 60 is
   suggested.

           +-------+--------+--------------------------+------------+
           | Value |  Hex   |    Endpoint function     | Reference  |
           +-------+--------+--------------------------+------------+
           | TBD   |  TBD   |    End.BIER              | This draft |
           +-------+--------+--------------------------+------------+

7.  Acknowledgements

   The authors would like to thank Stig Venaas for his valuable
   comments.  Thanks IJsbrand Wijnands, Greg Shepherd, Tony Przygienda,
   Toerless Eckert, Jeffrey Zhang for the helpful comments to improve
   this document.

8.  Contributors












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   Gang Yan
   Huawei Technologies
   China
   Email: yangang@huawei.com

   Yang(Yolanda) Xia
   Huawei Technologies
   China
   Email: yolanda.xia@huawei.com

9.  References

9.1.  Normative References

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
              2011, <https://www.rfc-editor.org/info/rfc6275>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [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>.

   [RFC8556]  Rosen, E., Ed., Sivakumar, M., Przygienda, T., Aldrin, S.,
              and A. Dolganow, "Multicast VPN Using Bit Index Explicit
              Replication (BIER)", RFC 8556, DOI 10.17487/RFC8556, April
              2019, <https://www.rfc-editor.org/info/rfc8556>.

9.2.  Informative References

   [I-D.ietf-bier-ipv6-requirements]
              McBride, M., Xie, J., Dhanaraj, S., and R. Asati, "BIER
              IPv6 Requirements", draft-ietf-bier-ipv6-requirements-01
              (work in progress), July 2019.





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   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J.,
              daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
              Network Programming", draft-ietf-spring-srv6-network-
              programming-01 (work in progress), July 2019.

   [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>.

Authors' Addresses

   Jingrong Xie
   Huawei Technologies

   Email: xiejingrong@huawei.com


   Liang Geng
   China Mobile
   Beijing 10053

   Email: gengliang@chinamobile.com


   Mike McBride
   Futurewei

   Email: mmcbride7@gmail.com


   Rajiv Asati
   Cisco

   Email: rajiva@cisco.com


   Senthil Dhanaraj
   Huawei

   Email: senthil.dhanaraj@huawei.com





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