Updates to the IPv6 Multicast Addressing Architecture
draft-ietf-6man-multicast-addr-arch-update-00

6man Working Group                                          M. Boucadair
Internet-Draft                                            France Telecom
Updates: 3306,3956,4607,4291 (if approved)                     S. Venaas
Intended status: Standards Track                                   Cisco
Expires: October 10, 2013                                 April 08, 2013

         Updates to the IPv6 Multicast Addressing Architecture
             draft-ietf-6man-multicast-addr-arch-update-00

Abstract

   This document updates the IPv6 multicast addressing architecture by
   defining the 17-20 reserved bits as generic flag bits.  The document
   provides also some clarifications related to the use of these flag
   bits.

   This document updates RFC 3956, RFC 3306, RFC 4607 and RFC 4291.

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
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   This Internet-Draft will expire on October 10, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Addressing Architecture Update  . . . . . . . . . . . . . . .   2
   3.  Clarifications  . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Flag Bits . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  IANA Assigned SSM Block . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   This document updates the IPv6 multicast addressing architecture
   [RFC4291] by defining the 17-20 reserved bits as generic flag bits
   (Section 2).  The document provides also some clarifications related
   to the use of these flag bits (Section 3.1) and also about IANA
   assigned SSM blocks (Section 3.2).

   This document updates [RFC3956], [RFC3306], [RFC4607] and [RFC4291].

2.  Addressing Architecture Update

   Bits 17-20 of a multicast address are defined in [RFC3956] and
   [RFC3306] as reserved bits.  This document defines these bits as
   generic flag bits so that they apply to any multicast address.
   Figure 1 and Figure 2 show the updated structure of the addressing
   architecture.  The first diagram shows the update of the base IPv6
   addressing architecture, and the second shows the update of so-called
   Embedded-RP.

    OLD:
    |   8    |  4 |  4 |                  112 bits                    |
    +--------+----+----+----------------------------------------------+
    |11111111|flgs|scop|                  group ID                    |
    +--------+----+----+----------------------------------------------+

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    NEW:
    |   8    |  4 |  4 |  4 |             108 bits                    |
    +--------+----+----+----------------------------------------------+
    |11111111|flgs|scop|flgs|             group ID                    |
    +--------+----+----+----+-----------------------------------------+

         Figure 1: Updated IPv6 Multicast Addressing Architecture

    OLD (RFC3956):
    |   8    |  4 |  4 |  4 |  4 |   8    |       64       |    32    |
    +--------+----+----+----+----+--------+----------------+----------+
    |11111111|flgs|scop|rsvd|RIID|  plen  | network prefix | group ID |
    +--------+----+----+----+----+--------+----------------+----------+

    NEW:
    |   8    |  4 |  4 |  4 |  4 |   8    |       64       |    32    |
    +--------+----+----+----+----+--------+----------------+----------+
    |11111111|flgs|scop|flgs|RIID|  plen  | network prefix | group ID |
    +--------+----+----+----+----+--------+----------------+----------+

      Figure 2: Embedded-RP with Updated IPv6 Multicast Address Arch.

   Further specification documents may define a meaning for these flag
   bits.  Defining the bits 17-20 as flags for all IPv6 multicast
   addresses allows addresses to be treated in a more uniform and
   generic way, and allows for these bits to be defined in the future
   for different purposes, irrespective of the specific type of
   multicast address.

3.  Clarifications

3.1.  Flag Bits

   Some implementations and specification documents do not treat the
   flag bits as separate bits but tend to use their combined value as a
   4-bit integer.  This practice is a hurdle for assigning a meaning to
   the remaining flag bits.  Below are listed some examples for
   illustration purposes:

   o  the reading of [RFC4607] may lead to conclude that ff3x::/32 is
      the only allowed SSM IPv6 prefix block.

   o  [RFC3956] states only ff70::/12 applies to Embedded-RP.
      Particularly, implementations should not treat the fff0::/12 range
      as Embedded-RP.

   To avoid such confusion and to unambiguously associate a meaning with
   the remaining flags, the following recommendation is made

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      Implementations MUST treat flag bits as separate bits.

3.2.  IANA Assigned SSM Block

   Another issue related to SSM is the IANA assigned SSM address block.
   Per [RFC4607], ff3x::4000:0001 through ff3x::7fff:fff is the block
   for IANA assignments (http://www.iana.org/assignments/ipv6-multicast-
   addresses/ipv6-multicast-addresses.xml).  However, IANA assignments
   are permanent addresses and should not have the transient bit set.
   Quoting from [RFC4607]:

      "T = 1 indicates a non-permanently-assigned ("transient")
      multicast address.".

4.  IANA Considerations

   This document may require IANA updates.  However, at this point it is
   not clear exactly what these updates may be.

5.  Security Considerations

   Security considerations discussed in [RFC3956], [RFC3306], [RFC4607]
   and [RFC4291] MUST be taken into account.

6.  Acknowledgements

   Many thanks to B.  Haberman for the discussions prior to the
   publication of this document.

7.  Normative References

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

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

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

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

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

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Authors' Addresses

   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com

   Stig Venaas
   Cisco
   USA

   Email: stig@cisco.com

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