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Versions: 00 01 02 03 04 05 06

Network Working Group                                  M. Boucadair, Ed.
Internet-Draft                                            France Telecom
Updates: 7371 (if approved)                                       J. Qin
Intended status: Standards Track                                   Cisco
Expires: March 28, 2015                                           Y. Lee
                                                                 Comcast
                                                               S. Venaas
                                                           Cisco Systems
                                                                   X. Li
                                       CERNET Center/Tsinghua University
                                                                   M. Xu
                                                     Tsinghua University
                                                      September 24, 2014


      IPv6 Multicast Address With Embedded IPv4 Multicast Address
            draft-ietf-mboned-64-multicast-address-format-06

Abstract

   This document reserves one bit (M-bit) of the unicast prefix-based
   multicast IPv6 address for ASM and an IPv6 multicast prefix for SSM
   mode to be used in the context of IPv4-IPv6 interconnection.

   The document specifies an algorithmic translation of an IPv6
   multicast address to a corresponding IPv4 multicast address, and vice
   versa.  This algorithmic translation can be used in both IPv4-IPv6
   translation or encapsulation schemes.

   This document updates RFC 7371.

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 RFC 2119 [RFC2119].

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





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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 March 28, 2015.

Copyright Notice

   Copyright (c) 2014 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
   (http://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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IPv4-Embedded IPv6 Multicast Prefix & Address . . . . . . . .   4
     3.1.  ASM Mode  . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  SSM Mode  . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  IPv4-Embedded IPv6 Multicast Address  . . . . . . . . . .   5
     3.4.  Address Translation Algorithm . . . . . . . . . . . . . .   6
     3.5.  Textual Representation  . . . . . . . . . . . . . . . . .   6
     3.6.  Source IPv4 Address in the IPv6 Realm . . . . . . . . . .   6
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Motivations  . . . . . . . . . . . . . . . . . . . .   9
     A.1.  Why an Address Format is Needed for Multicast IPv4-IPv6
           Interconnection?  . . . . . . . . . . . . . . . . . . . .   9
     A.2.  Why Identifying an IPv4-Embedded IPv6 Multicast Address
           is Required?  . . . . . . . . . . . . . . . . . . . . . .   9
     A.3.  Location of the IPv4 Address  . . . . . . . . . . . . . .  10
   Appendix B.  Design Considerations  . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11



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1.  Introduction

   Various solutions (e.g., [I-D.ietf-softwire-mesh-multicast],
   [I-D.ietf-softwire-dslite-multicast]) have been proposed to allow
   access to IPv4 multicast content from hosts attached to IPv6-enabled
   domains.  Even if these solutions have distinct applicability scopes
   (translation vs. encapsulation) and target different use cases, they
   all make use of specific IPv6 multicast addresses to embed an IPv4
   multicast address.  Particularly, the IPv4-Embedded IPv6 Multicast
   Address is used as a destination IPv6 address of multicast flows
   received from an IPv4-enabled domain and injected by the IPv4-IPv6
   Interconnection Function into an IPv6-enabled domain.  It is also
   used to build an IPv6 multicast state (*, G6) or (S6, G6)
   corresponding to their (*, G4) or (S4, G4) IPv4 counter parts by the
   IPv4-IPv6 Interconnection Function.  [I-D.ietf-mboned-v4v6-mcast-ps]
   provides more discussion about issues related to IPv4/IPv6 multicast.

   This document reserves one bit of the unicast prefix-based multicast
   IPv6 address ([RFC7371]) for Any-Source Multicast (ASM) mode and an
   IPv6 multicast prefix for Source-Specific Multicast (SSM) mode to be
   used in the context of IPv4-IPv6 interconnection.  This document also
   defines how IPv4-Embedded IPv6 Multicast Addresses are constructed.
   Both IPv4-IPv6 translation and encapsulation schemes can make use of
   this specification.

   This specification can be used in conjunction with other extensions
   such as embedding the rendezvous point [RFC3956].  Unicast prefix-
   based and embedded-RP techniques are important tools to simplify IPv6
   multicast deployments.  Indeed, unicast prefix-based IPv6 addressing
   is used in many current IPv6 multicast deployments, and has also been
   defined for IPv4, and is seen as a very useful technique.  Also
   embedded-RP is used in existing deployments.

   This document is a companion document to [RFC6052] which focuses
   exclusively on IPv4-embedded IPv6 unicast addresses.

2.  Terminology

   This document makes use of the following terms:

   o  IPv4-Embedded IPv6 Multicast Address: denotes a multicast IPv6
      address which includes in 32 bits an IPv4 address.

   o  Multicast Prefix64 (or MPREFIX64 for short) refers to an IPv6
      multicast prefix to be used to construct IPv4-Embedded IPv6
      Multicast Addresses.  This prefix is used to build an
      IPv4-Embedded IPv6 Multicast Address as defined in Section 3.4.




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      Section 3.4 specifies also how to extract an IPv4 address from an
      IPv4-Embedded IPv6 Multicast Address.

   o  ASM_MPREFIX64: denotes a multicast Prefix64 used in Any Source
      Multicast (ASM) mode.

   o  SSM_MPREFIX64: denotes a multicast Prefix64 used in Source
      Specific Multicast (SSM) mode.

   o  IPv4-IPv6 Interconnection Function: refers to a function which is
      enabled in a node interconnecting an IPv4-enabled domain with an
      IPv6-enabled one.  It can be located in various places of the
      multicast network.  Particularly, in terms of multicast control
      messages, it can be an IGMP/MLD Interworking Function or an
      IPv4-IPv6 PIM Interworking Function.  An IPv4-IPv6 Interconnection
      Function is configured with one or two MPREFIX64s.

3.  IPv4-Embedded IPv6 Multicast Prefix & Address

3.1.  ASM Mode

   The format specified in Figure 1 uses some bits defined in [RFC7371]:
   M-bit (20th bit position, where bit 1 is the most significant bit)
   now has a meaning.

   Details on design considerations are discussed in Appendix B.

   |   8    |  4 |  4 |  4 |             76               |    32    |
   +--------+----+----+----+------------------------------+----------+
   |11111111|ff1 |scop|ff2 |         sub-group-id         |v4 address|
   +--------+----+----+----+-----------------------------------------+
                                                     +-+-+-+-+
      ff2 (flag field 2) is a set of 4 flags:        |r|r|r|M|
                                                     +-+-+-+-+

      "r" bits MUST each be set to 0.


      Figure 1: IPv4-Embedded IPv6 Multicast Address Format: ASM Mode

   The description of the fields is as follows:

   o  ff1 field is defined in [RFC7371].
   o  "scop" field is defined in [RFC3956].
   o  M (20th bit position): When this bit is set to 1, it indicates
      that a multicast IPv4 address is embedded in the low-order 32 bits
      of the multicast IPv6 address.




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   o  sub-group-id: This field is configurable according to local
      policies (e.g., enable embedded-RP) of the entity managing the
      IPv4-IPv6 Interconnection Function.  This field MUST follow the
      recommendations specified in [RFC3306] if unicast-based prefix is
      used or the recommendations specified in [RFC3956] if embedded-RP
      is used.  The default value is all zeros.
   o  The low-order 32 bits MUST include an IPv4 multicast address when
      the M-bit is set to 1.  The enclosed IPv4 multicast address SHOULD
      NOT be in 232/8 range.

3.2.  SSM Mode

   For SSM mode, and given what is discussed in Appendix B, the
   following IPv6 prefix to embed IPv4 multicast addresses is reserved:

   o  ff3x:0:8000::/96 ('x' is any valid scope).

3.3.  IPv4-Embedded IPv6 Multicast Address

   For the delivery of the IPv4-IPv6 multicast interconnection services,
   a dedicated multicast prefix denoted as MPREFIX64 should be
   provisioned (e.g., using NETCONF or
   [I-D.ietf-softwire-multicast-prefix-option]) to any function
   requiring to build an IPv4-Embedded IPv6 Multicast Address based on
   an IPv4 multicast address.  MPREFIX64 can be of ASM or SSM type.
   When both modes are used, two prefixes are required to be
   provisioned.

   The length of MPREFIX64 MUST be /96.  For SSM, MPREFIX64 MUST be
   equal to ff3x:0:8000::/96.  For the ASM mode, MPREFIX64 MUST have the
   M-bit set to 1.  Furthermore, the format of the ASM_MPREFIX64 should
   follow what is specified in [RFC3306] and [RFC3956] if corresponding
   mechanisms are used.  If not, bits 21-96 can be set to any value.

   Figure 2 shows how to build an IPv4-Embedded IPv6 Multicast Address
   using a configured MPREFIX64 and an IPv4 multicast address.  The low-
   order 32 bits MUST include an IPv4 multicast address.  The enclosed
   IPv4 multicast address SHOULD NOT be in 232/8 range if an
   ASM_PREFIX64 is configured.  The enclosed IPv4 multicast address
   SHOULD be in 232/8 range if an SSM_PREFIX64 is configured.

   Embedding an IPv4 multicast address in the last 32 bits does not
   conflict with the Group IDs assigned by IANA (i.e., 0x00000001 to
   0x3FFFFFFF [RFC3307]).

   When several MPREFIX64 are available, it is RECOMMENDED to use the
   MPREFIX64 which preserve the scope of the IPv4 multicast address.




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   |                             96                       |    32    |
   +------------------------------------------------------+----------+
   |                         MPREFIX64                    |v4 address|
   +------------------------------------------------------+----------+


           Figure 2: IPv4-Embedded IPv6 Multicast Address Format

3.4.  Address Translation Algorithm

   IPv4-Embedded IPv6 Multicast Addresses are composed according to the
   following algorithm:

   o  Concatenate the MPREFIX64 and the 32 bits of the IPv4 address to
      obtain a 128-bit address.

   The IPv4 multicast addresses are extracted from the IPv4-Embedded
   IPv6 Multicast Addresses according to the following algorithm:

   o  If the multicast address has the 20th bit set to 1 or it matches
      ff3x:0:8000::/96 or a preconfigured MPREFIX64, extract the last 32
      bits of the IPv6 multicast address.

3.5.  Textual Representation

   The embedded IPv4 address in an IPv6 multicast address is included in
   the last 32 bits; therefore dotted decimal notation can be used.

3.6.  Source IPv4 Address in the IPv6 Realm

   An IPv4 source is represented in the IPv6 realm with its
   IPv4-converted IPv6 address [RFC6052].

4.  Examples

   Figure 3 provides some examples of ASM IPv4-Embedded IPv6 Address
   while Figure 4 provides an example of SSM IPv4-Embedded IPv6 Address.

   IPv4 multicast addresses used in the examples are derived from the
   IPv4 multicast block reserved for documentation in [RFC6676].











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   +----------------------+--------------+-----------------------------+
   |     MPREFIX64        | IPv4 address | IPv4-Embedded IPv6 Address  |
   +----------------------+--------------+-----------------------------+
   | ff3x:z000:0:abc::/96 |  233.252.0.1 |ff3x:z000:0:abc::233.252.0.1 |
   | ff7x:z000:0:abc::/96 |  233.252.0.2 |ff7x:z000:0:abc::233.252.0.2 |
   +----------------------+--------------+-----------------------------+
   where:
     "x" is any valid scope
     "z" is any 4 bits where the last bit is set (e.g., 1, 3, 7, ...)

            Figure 3: Example of ASM IPv4-embedded IPv6 address

    +---------------------+--------------+----------------------------+
    |      MPREFIX64      | IPv4 address | IPv4-Embedded IPv6 Address |
    +---------------------+--------------+----------------------------+
    |   ff3x:0:8000::/96  | 233.252.0.5  |   ff3x:0:8000::233.252.0.5 |
    +---------------------+--------------+----------------------------+

            Figure 4: Example of SSM IPv4-embedded IPv6 address

5.  IANA Considerations

   This document requests IANA to reserve:

   o  ff3x:0:8000::/96 SSM range to embed an IPv4 multicast address in
      the last 32 bits.

6.  Security Considerations

   This document defines an algorithmic translation of an IPv6 multicast
   address into an IPv4 multicast address, and vice versa.  The security
   considerations discussed in [RFC6052] are to be taken into
   consideration.

7.  Acknowledgements

   Many thanks to R.  Bonica, B.  Sarikaya, P.  Savola, T.  Tsou, C.
   Bormann, T.  Chown, P.  Koch, B.  Haberman, and B.  Hinden for their
   comments and review.

8.  References

8.1.  Normative References

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





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   [RFC3306]  Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
              Multicast Addresses", RFC 3306, August 2002.

   [RFC3307]  Haberman, B., "Allocation Guidelines for IPv6 Multicast
              Addresses", RFC 3307, August 2002.

   [RFC3956]  Savola, P. and B. Haberman, "Embedding the Rendezvous
              Point (RP) Address in an IPv6 Multicast Address", RFC
              3956, November 2004.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, August 2006.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

   [RFC7371]  Boucadair, M. and S. Venaas, "Updates to the IPv6
              Multicast Addressing Architecture", RFC 7371, September
              2014.

8.2.  Informative References

   [I-D.ietf-mboned-v4v6-mcast-ps]
              Jacquenet, C., Boucadair, M., Lee, Y., Qin, J., Tsou, T.,
              and Q. Qiong, "IPv4-IPv6 Multicast: Problem Statement and
              Use Cases", draft-ietf-mboned-v4v6-mcast-ps-04 (work in
              progress), September 2013.

   [I-D.ietf-softwire-dslite-multicast]
              Qin, J., Boucadair, M., Jacquenet, C., Lee, Y., and Q.
              Wang, "Delivery of IPv4 Multicast Services to IPv4 Clients
              over an IPv6 Multicast Network", draft-ietf-softwire-
              dslite-multicast-08 (work in progress), September 2014.

   [I-D.ietf-softwire-mesh-multicast]
              Xu, M., Cui, Y., Wu, J., Yang, S., Metz, C., and G.
              Shepherd, "Softwire Mesh Multicast", draft-ietf-softwire-
              mesh-multicast-07 (work in progress), July 2014.

   [I-D.ietf-softwire-multicast-prefix-option]
              Boucadair, M., Qin, J., Tsou, T., and X. Deng, "DHCPv6
              Option for IPv4-Embedded Multicast and Unicast IPv6
              Prefixes", draft-ietf-softwire-multicast-prefix-option-07
              (work in progress), September 2014.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.



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   [RFC6676]  Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and
              M. Eubanks, "Multicast Addresses for Documentation", RFC
              6676, August 2012.

   [RFC7051]  Korhonen, J. and T. Savolainen, "Analysis of Solution
              Proposals for Hosts to Learn NAT64 Prefix", RFC 7051,
              November 2013.

Appendix A.  Motivations

A.1.  Why an Address Format is Needed for Multicast IPv4-IPv6
      Interconnection?

   Arguments why an IPv6 address format is needed to embed multicast
   IPv4 address are quite similar to those of [RFC6052].  Concretely,
   the definition of a multicast address format embedding a multicast
   IPv4 address allows:

   o  Stateless IPv4-IPv6 header translation of multicast flows;

   o  Stateless IPv4-IPv6 PIM interworking function;

   o  Stateless IGMP-MLD interworking function (e.g., required for an
      IPv4 receiver to access to IPv4 multicast content via an IPv6
      network);

   o  Stateless (local) synthesis of IPv6 address when IPv4 multicast
      address are embedded in application payload (e.g., SDP [RFC4566]);

   o  Except the provisioning of the same MPREFIX64, no coordination is
      required between IPv4-IPv6 PIM interworking function, IGMP-MLD
      interworking function, IPv4-IPv6 Interconnection Function and any
      ALG (Application Level Gateway) in the path;

   o  Minimal operational constraints on the multicast address
      management: IPv6 multicast addresses can be constructed using what
      has been deployed for IPv4 delivery mode.

A.2.  Why Identifying an IPv4-Embedded IPv6 Multicast Address is
      Required?

   Reserving a dedicated multicast prefix for IPv4-IPv6 interconnection
   purposes is a means to guide the address selection process at the
   receiver side; in particular it assists the receiver to select the
   appropriate IP multicast address while avoiding to involve an
   IPv4-IPv6 interconnection function in the path.

   Two use cases to illustrate this behavior are provided below:



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   1.  An ALG is required to help an IPv6 receiver to select the
       appropriate IP address when only the IPv4 address is advertised
       (e.g., using SDP); otherwise the access to the IPv4 multicast
       content can not be offered to the IPv6 receiver.  The ALG may be
       located downstream the receiver.  As such, the ALG does not know
       in advance whether the receiver is dual-stack or IPv6-only.  The
       ALG may be tuned to insert both the original IPv4 address and
       corresponding IPv6 multicast address.  If a dedicated prefix is
       not used, a dual-stack receiver may prefer to use the IPv6
       address to receive the multicast content.  This address selection
       would require multicast flows to cross an IPv4-IPv6
       interconnection function.

   2.  In order to avoid involving an ALG in the path, an IPv4-only
       source can advertise both its IPv4 address and IPv4-Embedded IPv6
       Multicast Address.  If a dedicated prefix is not reserved, a
       dual-stack receiver may prefer to use the IPv6 address to receive
       the multicast content.  This address selection would require
       multicast flows to cross an IPv4-IPv6 interconnection function.

   Reserving dedicated IPv6 multicast prefixes for IPv4-IPv6
   interconnection purposes mitigates the issues discussed in [RFC7051]
   in a multicast context.

A.3.  Location of the IPv4 Address

   There is no strong argument to allow for flexible options to encode
   the IPv4 address inside the multicast IPv6 address.  The option
   retained by the authors is to encode the multicast IPv4 address in
   the low-order 32 bits of the IPv6 address.

   This choice is also motivated by the need to be compliant with
   [RFC3306] and [RFC3956].

Appendix B.  Design Considerations

   The following constraints should be met when reserving dedicated
   prefix(es) to be used for IPv4/IPv6 multicast interconnection:

   1:  Belong to SSM prefix range (preferably ff3x::/32) and be
       compatible with unicast-based prefix [RFC3306] for SSM.  Note
       that [RFC3306] suggests to set "plen" to 0 and "network-prefix"
       to 0.  As such, any prefix in the 33-96 range can be convenient.
       Given [RFC4607] indicates future specifications may allow a non-
       zero network prefix field, a /33 would allow for future
       extensions but it has the drawback of reserving a large block.  A
       /96 would be adequate for the use cases already identified in




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       [I-D.ietf-mboned-v4v6-mcast-ps].  In the event of any concrete
       extension, reserving additional prefixes may be considered.

   2:  Be compatible with embedded-RP [RFC3956] and unicast-based prefix
       [RFC3306] for ASM.  This results in associating a meaning with
       one of the reserved bits in [RFC7371].  Defining the 17-20 bits
       range to have a meaning and be used for IPv4/IPv6 transition has
       the advantage of allowing for future extensions but it may be
       seen as a waste of the multicast address space.  Consequently,
       using one of the reserved bits (in the range 17-20) from the
       unicast-based IPv6 multicast address format [RFC3306] is
       preferred.

   Meeting (1) and (2) with the same reserved bit is not feasible
   without modifying embedded-RP and unicast-based prefix
   specifications; this option is avoided.

   As a consequence, this document proposes to reserve a multicast
   prefix for SSM and define one bit of the unicast prefix-based
   multicast IPv6 address for ASM when embedding IPv4 multicast address
   in an IPv6 multicast address.

Authors' Addresses

   Mohamed Boucadair (editor)
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Jacni Qin
   Cisco
   China

   Email: jacni@jacni.com


   Yiu L. Lee
   Comcast
   U.S.A

   Email: yiu_lee@cable.comcast.com







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   Stig Venaas
   Cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: stig@cisco.com


   Xing Li
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   P.R. China

   Phone: +86 10-62785983
   Email: xing@cernet.edu.cn


   Mingwei Xu
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-10-6278-5822
   Email: xmw@cernet.edu.cn
























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