Internet DRAFT - draft-perreault-pim-igmp-mld-translation

draft-perreault-pim-igmp-mld-translation






Network Working Group                                       S. Perreault
Internet-Draft                                                  Viagenie
Intended status: Standards Track                                 T. Tsou
Expires: August 19, 2013                       Huawei Technologies (USA)
                                                       February 15, 2013


Internet Group Management Protocol (IGMP) / Multicast Listener Discovery
       (MLD)-Based Multicast Translation ("IGMP/MLD Translation")
              draft-perreault-pim-igmp-mld-translation-00

Abstract

   This document describes translation between IGMP and MLD.  This
   allows single-stack multicast nodes to participate in multicast
   groups from a different address family.  Both sending and receiving
   is supported by this translation mechanism.  Both any-source and
   source-specific multicast (ASM and SSM) are supported as well.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

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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 August 19, 2013.

Copyright Notice

   Copyright (c) 2013 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
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   (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



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   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.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Overview of Implementation Types . . . . . . . . . . . . . . .  4
     4.1.  Proxy  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
       4.1.1.  Mixed IPv4/IPv6 Networks . . . . . . . . . . . . . . .  5
     4.2.  Multicast Router . . . . . . . . . . . . . . . . . . . . .  6
   5.  Signalling Translation . . . . . . . . . . . . . . . . . . . .  6
     5.1.  IP Headers . . . . . . . . . . . . . . . . . . . . . . . .  6
       5.1.1.  Addresses  . . . . . . . . . . . . . . . . . . . . . .  6
       5.1.2.  Router-Alert Option  . . . . . . . . . . . . . . . . .  7
     5.2.  IGMP/MLD Translation . . . . . . . . . . . . . . . . . . .  7
       5.2.1.  Message Type Equivalences  . . . . . . . . . . . . . .  7
       5.2.2.  The "Translated" Bit . . . . . . . . . . . . . . . . .  8
       5.2.3.  Maximum Response {Delay,Time}  . . . . . . . . . . . . 12
       5.2.4.  Multicast Group Address  . . . . . . . . . . . . . . . 13
       5.2.5.  Source Addresses . . . . . . . . . . . . . . . . . . . 14
       5.2.6.  Additional and Auxiliary Data  . . . . . . . . . . . . 14
     5.3.  MTU Considerations . . . . . . . . . . . . . . . . . . . . 14
   6.  Data Transfer  . . . . . . . . . . . . . . . . . . . . . . . . 14
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   10. Normative References . . . . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16




















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1.  Introduction

   This document specifies IGMP/MLD translation, a mechanism for IPv4-
   IPv6 transition and coexistence.  It enables single-stack (i.e.,
   IPv4-only or IPv6-only) hosts to participate, either as listeners,
   sources, or both, in multicast groups belonging to a different
   address family.

   This translation mechanism is intended to be considered as a "virtual
   function" that can be implemented in a listener, in a multicast
   router, in an IGMP/MLD proxy [RFC4605], in existing layer-2 equipment
   (i.e. as a "bump in the wire"), or as a standalone translating
   device.  Therefore, this function could be located at the customer
   network edge (e.g., in customer-premises equipment (CPE)) or at the
   provider network edge (e.g., in a DSLAM for DSL networks, in a CMTS
   for cable networks, etc.), or any other node reachable by IGMP/MLD
   packets.  Note that intputs and outputs of this translation function
   can also be virtual.  For example, translated packets need not
   actually be sent on the wire if the function's output is fed directly
   into a multicast router process (e.g., a PIM daemon) running on the
   same host.


2.  Terminology

   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].

   The unqualified term "proxy" refers to an IGMP/MLD proxy as defined
   in [RFC4605].


3.  Overview

   The translation function produces IGMPv1,2,3 packets from MLDv1,2
   packets and vice-versa.

                               +-------------+
                      IGMPv1 --|             |-- MLDv1
                      IGMPv2 --| Translation |-- MLDv2
                      IGMPv3 --|   <----->   |
                               +-------------+

                       Virtual translation function

   IPv4 addresses are mapped to IPv6 addresses and vice versa as defined
   in [I-D.boucadair-64-multicast-address-format].  This mapping is



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   stateless.  This implies that arbitrary IPv6 addresses are not
   handled.  IPv6 addresses MUST be part of a predetermined prefix in
   order to be translateable.

   The statelessness of the translation function is considered a
   desirable property, and is an objective of this specification.  In
   general, stateless network elements makes simpler designs, allows
   better scalability, and requires less operational overhead.

   This translation function is stateless when considering full IGMP or
   MLD packets.  Fragmented packets MUST be reassembled before they can
   be fed to this translation function.


4.  Overview of Implementation Types

   The virtual translation function defined in this document can be
   implemented in various ways.  This section presents an overview of
   some possibilities.

4.1.  Proxy

   As described in [RFC4605], an IGMP/MLD proxy is located between an
   upstream network and one or more downstream networks.  Listeners are
   in the downstream networks while the rest of the multicast
   infrastructure is upstream.  It is possible to arrange multiple
   proxies in a tree topology, where one proxy's upstream network is
   another's downstream network.

   The translation function MUST be logically situated between the proxy
   function and the upstream network, as shown in Figure 1.

                                 Upstream
                                    |
                               +----+-----+
                               |Translator|
                               +----+-----+
                                    |
                                +---+----+
                                | Proxy  |
                                +-+-+-+-++
                                  | | | |
                               Downstream(s)

               Figure 1: IGMP/MLD translator proxy topology

   There are two reasons for locating the translator upstream of the
   proxy rather than downstream:



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   1.  Translating addresses on downstream interfaces could interfere
       with Querier elections.  As described in [RFC3376] section 6.6.2
       and [RFC3810] section 7.6.2, IGMP and MLD routers elect a Querier
       amongst themselves.  The criteria for winning the election is
       based on the source address of IGMP/MLD Queries.  Having a
       translator on a downstream interface would impose a new
       constraint on the address mapping scheme: it would need to ensure
       the same election result before and after applying the mapping.
       This constraint is lifted when the translation is applied to the
       upstream interface instead.  Since a proxy acts as a client on
       its upstream interface, it does not participate in Querier
       elections.

   2.  There is only one upstream interface whereas there may be
       multiple downstream interfaces.  Applying the translation on the
       upstream interface has the advantage of having a single
       translation point, which can facilitate debugging and
       troubleshooting.

   Conceptually, translation is applied to messages sent upstream by the
   client state machine and to messages received from upstream.  This
   document specifies how translation is carried out in terms of packet
   translation.  However, a particular implementation is at liberty to
   adopt any internal structure as long as externally observable
   behavior is identical.

4.1.1.  Mixed IPv4/IPv6 Networks

   In mixed networks, where there may be both IPv4 and IPv6 receivers,
   two logical proxies are used.  Each maintains membership state and
   runs state machines in the address families of the receivers it is
   proxying.  Translation is applied to only one of them.  This is
   illustrated in Figure 2.

                                  Upstream
                             +-----IPvX-----+
                             |              |
                        +----+-----+        |
                        |Translator|        |
                        +----+-----+        |
                             |              |
                       +---+--------+ +-----+------+
                       | Proxy IPvY | | Proxy IPvX |
                       +-+-+-+-+-+--+ +-+-+-+-+-+--+
                         | | | | |      | | | | |
                       Downstream(s)   Downstream(s)
                           IPvX            IPvX




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                    Figure 2: Mixed IPv4/IPv6 topology

4.2.  Multicast Router

   When implemented as part of a multicast router, the translation
   function is logically situated on the downstream interfaces, as shown
   in Figure 3.  In this example, the router speaks PIM on an upstream
   interface and IGMP/MLD on a downstream interface.

                                   PIM
                                    |
                                +--------+
                                | Router |
                                +--------+
                                    |
                              +-------------+
                              | Translation |
                              +-------------+
                                    |
                                 IGMP/MLD

               Figure 3: IGMP/MLD translator router topology

   Note that the translation function can be completely virtual in this
   case, as long as the externally observable behavior conforms to this
   specification.


5.  Signalling Translation

   This section describes how to translate between IGMP and MLD.

5.1.  IP Headers

5.1.1.  Addresses

   Destination addresses are translated as follows:

   MLDv2 and IGMPv3:  The destination address is a well-known address
      and is translated as listed in Table 1.

   MLDv1, IGMPv1, and IGMPv2:  The destination address corresponds to
      the address of the multicast group.  The multicast group address
      is mapped between IPv4 and IPv6 as described in
      [I-D.boucadair-64-multicast-address-format].






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     +--------------------------------------+------------+----------+
     | Description                          | IPv4       | IPv6     |
     +--------------------------------------+------------+----------+
     | All nodes on link                    | 224.0.0.1  | ff02::1  |
     | All routers on link                  | 224.0.0.2  | ff02::2  |
     | All IGMP/MLD-capable routers on link | 224.0.0.22 | ff02::16 |
     +--------------------------------------+------------+----------+

       Table 1: IPv4/IPv6 Well-Known Multicast Address Equivalences

   Source addresses are translated as follows:

   IGMP to MLD:  The source address is set to a link-local IPv6 address
      assigned to the proxy's upstream interface.

   MLD to IGMP:  The source address is set to the IPv4 address assigned
      to the proxy's upstream interface.

   IGMP and MLD Reports having an unspecified source address (0.0.0.0 or
   ::) are handled differently.  In MLD, they are dropped ([RFC3810]
   section 5.2.13).  In IGMP, they are accepted ([RFC3376] section
   4.2.13).  This means that translating 0.0.0.0 to :: and vice-versa
   would change the router's behaviour: it would accept a message that
   should have been dropped, and vice-versa.  To eliminate this
   ambiguity, the translator MUST drop IGMP and MLD reports having an
   unspecified source address.

5.1.2.  Router-Alert Option

   IGMP messages are sent with a Router Alert IPv4 option [RFC2113]
   while MLD message are sent with a Router Alert option in a Hop-By-Hop
   IPv6 extension header [RFC2711].  The translator needs to convert
   between these two.  The value MUST be set to zero unconditionally
   because the IPv4 and IPv6 value spaces are not identical.

5.2.  IGMP/MLD Translation

5.2.1.  Message Type Equivalences

   The IGMP/MLD messages to be handled by the translator belong to the
   proxy's upstream interface, on which the proxy acts as a listener.
   This means that translation will be applied to IGMP/MLD Reports and
   Leave/Done messages sent from the proxy as well as to to IGMP/MLD
   Queries received from routers.

   Upon reception of an IGMP message with a type field containing one of
   the values listed in Table 2, the translator will intercept the
   message and produce an equivalent MLDv2 message corresponding to an



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   ICMPv6 message with the listed type number in the same row.  The
   translator will perform the reverse operation upon reception of an
   MLDv2 message.

              +-----------------------+--------------------+
              | IGMP type number      | ICMPv6 type number |
              +-----------------------+--------------------+
              | 17 IGMPv1/v2/v3 Query | 130 MLDv1/v2 Query |
              | 18 IGMPv1 Report      | 131 MLDv1 Report   |
              | 22 IGMPv2 Report      | 131 MLDv1 Report   |
              | 23 IGMPv2 Leave       | 132 MLDv1 Done     |
              | 34 IGMPv3 Report      | 143 MLDv2 Report   |
              +-----------------------+--------------------+

                Table 2: IGMP/MLD Message Type Equivalences

5.2.2.  The "Translated" Bit

   Experience IPv6 transition in general and translation in particular
   has shown that it is often useful, for various reasons, most often of
   an operational nature, that can not necessarily be anticipated at the
   time a specification gets written, to include a mechanism allowing
   the identification of translated traffic.

   This specification tries to anticipate that need by assigning a
   reserved bit in both IGMPv3 and MLDv2 for such a purpose.  When set
   to 1, it indicates a message that has been translated according to
   this specification at least once.  When set to 0, it indicates that
   no translation has been performed.

   A translator conforming to this specification MUST set the Translated
   bit to 1 on output.  The bit is ignored on input by default, meaning
   that a message could be translated twice or more.  This will often be
   undesirable, but is allowed by this specification.

   In an IGMPv3 Query, bit number 64 is the Translated bit, as shown in
   Figure 4.

   In an IGMPv3 Report, bit number 32 is the Translated bit, as shown in
   Figure 5.

   In an MLDv2 Query, bit number 192 is the Translated bit, as shown in
   Figure 6.

   In an MLDv2 Report, bit number 32 is the Translated bit, as shown in
   Figure 7.





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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 = 0x11  | Max Resp Code |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Group Address                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T|Resv |S| QRV |     QQIC      |     Number of Sources (N)     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Source Address [1]                      |
     +-                                                             -+
     |                       Source Address [2]                      |
     +-                              .                              -+
     .                               .                               .
     .                               .                               .
     +-                                                             -+
     |                       Source Address [N]                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 4: "Translated" bit in an IGMPv3 Query (identified by the
                                 letter T)






























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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 = 0x22  |    Reserved   |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T|         Reserved            |  Number of Group Records (M)  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                        Group Record [1]                       .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                        Group Record [2]                       .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               .                               |
     .                               .                               .
     |                               .                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                        Group Record [M]                       .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 5: "Translated" bit in an IGMPv3 Report (identified by the
                                 letter T)



















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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 = 130   |      Code     |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Maximum Response Code      |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     *                                                               *
     |                                                               |
     *                       Multicast Address                       *
     |                                                               |
     *                                                               *
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T|Resv |S| QRV |     QQIC      |     Number of Sources (N)     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     *                                                               *
     |                                                               |
     *                       Source Address [1]                      *
     |                                                               |
     *                                                               *
     |                                                               |
     +-                                                             -+
     |                                                               |
     *                                                               *
     |                                                               |
     *                       Source Address [2]                      *
     |                                                               |
     *                                                               *
     |                                                               |
     +-                              .                              -+
     .                               .                               .
     .                               .                               .
     +-                                                             -+
     |                                                               |
     *                                                               *
     |                                                               |
     *                       Source Address [N]                      *
     |                                                               |
     *                                                               *
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 6: "Translated" bit in an MLDv2 Query (identified by the
                                 letter T)




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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 = 143   |    Reserved   |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T|         Reserved            |Nr of Mcast Address Records (M)|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                  Multicast Address Record [1]                 .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                  Multicast Address Record [2]                 .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               .                               |
     .                               .                               .
     |                               .                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                  Multicast Address Record [M]                 .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 7: "Translated" bit in an MLDv2 Report (identified by the
                                 letter T)

5.2.3.  Maximum Response {Delay,Time}

   IGMPv2 and IGMPv3 queries contain a field specifying the Maximum
   Response Time (MRT), which is the maximum time allowed before sending
   a Report, expressed in units of 1/10 seconds.  Similarly, MLDv1 and
   MLDv2 queries contain a field specifying the Maximum Response Delay
   (MRD), expressed in units of milliseconds.

   IGMPv2 (resp. MLDv1) encode the MRT (resp. MRD) value directly as a
   binary integer.  IGMPv3 (resp. MLDv2) allows a floating-point
   encoding as well.

   IGMPv2 and IGMPv3 uses an 8-bit field while MLDv1 and MLDv2 use a 16-
   bit field.




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   The conversion algorithm is as follows:

   IGMPv2 to MLDv1:  MRD = 100 * MRT

      All values that can be represented in IGMPv2 can be equivalently
      represented in MLDv1 without loss of precision.

   IGMPv3 to MLDv2:  MRD = 100 * MRT

      All values that can be represented in IGMPv3 can be equivalently
      represented in MLDv2 without loss of precision.

      If MRT < 128, both MRT and MRD will be encoded as binary integers.

      If 128 <= MRT < 336, MRT will be encoded as a floating-point value
      while MRD will be encoded as a binary integer.

      If 336 <= MRT, both MRT and MRD will be encoded as floating-point
      values.

   MLDv1 to IGMPv2:  MRT = min(255, round(MRD / 100))

      The MRD is divided by 100, rounded to the nearest integer, then
      capped at 255 (the largest MRT value representable in IGMPv2).
      There is both precision and range loss.

   MLDv2 to IGMPv3:  MRT = min(31744, round(MRD / 100))

      The MRD is divided by 100, rounded to the nearest integer, then
      capped at 31744 (the largest MRT value representable in IGMPv3).
      There is both precision and range loss.

      If MRD < 12800, both MRD and MRT will be encoded as binary
      integers.

      If 12800 <= MRD < 32768, MRD will be encoded as a binary integer
      while MRT will be encoded as a floating-point value.

      If 32768 <= MRD, both MRD and MRT will be encoded as binary
      integers.

5.2.4.  Multicast Group Address

   The multicast group address is mapped between IPv4 and IPv6 as
   described in [I-D.boucadair-64-multicast-address-format].






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5.2.5.  Source Addresses

   Source addresses, if any, are mapped as follows:

   IGMP to MLD:  IPv4 source addresses are mapped as described in
      [RFC6052] section 2.2.

   MLD to IGMP:  An IPv4 address is extracted from an IPv6 source
      address as described in [RFC6052] section 2.2.  MLD messages
      containing a source address outside the IPv4-Embedded IPv6 Prefix
      are dropped unless there exists an applicable statically
      configured mapping.

5.2.6.  Additional and Auxiliary Data

   All IGMPv3 and MLDv2 messages can contain Additional Data, as defined
   in [RFC3376] sections 4.1.10 and 4.2.11 and [RFC3810] sections 5.1.12
   and 5.2.11.

   In addition, IGMPv3 and MLDv2 Reports can contain Auxiliary Data, as
   defined in [RFC3376] section 4.2.10 and [RFC3810] section 5.2.10.

   A translator MUST preserve Additional and Auxiliary Data.  This is
   accomplished by treating such data an an opaque blob and setting the
   appropriate IPv4 or ICMPv6 length fields appropriately.

5.3.  MTU Considerations

   MTU issues should be handled at the application layer, not at the IP
   layer.  That is, the translator MUST split large Report messages into
   smaller pieces that fit into an interface's MTU after translation, as
   described in [RFC3810] section 5.2.15 and [RFC3376] section 4.2.16..


6.  Data Transfer

   Note:  Should this section be removed?  We could say nothing about
      the data plane and instead focus exclusively on the signalling.
      Thoughts?

   The IGMP/MLD translator is configured either to translate the headers
   of multicast packets or to encapsulate/decapsulate them.  This
   applies to regular multicast traffic, not to IGMP/MLD signalling.

   Translation is performed according to [RFC6145], with the address
   mapping specified in [I-D.boucadair-64-multicast-address-format].
   IPv6 packets with a source or destination address outside MPREFIX64
   are dropped unless there exists an applicable statically configured



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   mapping.

   Encapsulation/decapsulation might be preferable when joining two IPvX
   islands across an IPvY network.  Interfaces on which encapsulation/
   decapsulation takes place are configured into the translator.  When
   encapsulating, the original packet is not modified.  If it is an IPv6
   packet, it gets encapsulated in an IPv4 packet, and vice-versa.  The
   addresses of the encapsulating packet are obtained by mapping those
   of the original packet according to
   [I-D.boucadair-64-multicast-address-format].  When decapsulating, the
   original packet is obtained from the encapsulating packet's payload
   and is forwarded as-is.  Refer to [RFC2473] for details.


7.  IANA Considerations

   TODO


8.  Security Considerations

   TODO


9.  Acknowledgements

   The authors wish to thank the following people for their feedback:
   Behcet Sarikaya, Dino Farinacci, Stig Venaas, and Tom Taylor.


10.  Normative References

   [I-D.boucadair-64-multicast-address-format]
              Boucadair, M., Qin, J., Lee, Y., Venaas, S., Li, X., and
              M. Xu, "IPv4-Embedded IPv6 Multicast Address Format",
              draft-boucadair-64-multicast-address-format-00 (work in
              progress), January 2012.

   [RFC2113]  Katz, D., "IP Router Alert Option", RFC 2113,
              February 1997.

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

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

   [RFC2711]  Partridge, C. and A. Jackson, "IPv6 Router Alert Option",



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              RFC 2711, October 1999.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC4605]  Fenner, B., He, H., Haberman, B., and H. Sandick,
              "Internet Group Management Protocol (IGMP) / Multicast
              Listener Discovery (MLD)-Based Multicast Forwarding
              ("IGMP/MLD Proxying")", RFC 4605, August 2006.

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

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, April 2011.


Authors' Addresses

   Simon Perreault
   Viagenie
   246 Aberdeen
   Quebec, QC  G1R 2E1
   Canada

   Phone: +1 418 656 9254
   Email: simon.perreault@viagenie.ca
   URI:   http://viagenie.ca


   Tina Tsou
   Huawei Technologies (USA)
   2330 Central Expressway
   Santa Clara, CA  95050
   USA

   Phone: +1 408 330 4424
   Email: tina.tsou.zouting@huawei.com








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