Updates to Dynamic IPv6 Multicast Address Group IDs
draft-ietf-pim-updt-ipv6-dyn-mcast-addr-grp-id-13

Network Working Group                                        N. Karstens
Internet-Draft                                                    Garmin
Updates: 3307 (if approved)                                 D. Farinacci
Intended status: Standards Track                             lispers.net
Expires: 10 September 2026                                    M. McBride
                                                               Futurewei
                                                            9 March 2026

          Updates to Dynamic IPv6 Multicast Address Group IDs
           draft-ietf-pim-updt-ipv6-dyn-mcast-addr-grp-id-13

Abstract

   This document describes limitations of the existing range of dynamic
   IPv6 multicast addresses specified in RFC3307, Allocation Guidelines
   for IPv6 Multicast Addresses.  It updates RFC3307 by replacing these
   allocations with a new IANA registry in the IPv6 Multicast Address
   Space registry group.  The document also defines initial contents of
   the new registry: a reduced allocation for the Multicast Address
   Dynamic Client Allocation Protocol (MADCAP; RFC2730), a range for
   SSM, a Private Use range, a range for Experimental Use, and
   Solicited-Node multicast addresses (which were not previously noted
   in RFC3307).

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 10 September 2026.

Copyright Notice

   Copyright (c) 2026 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 (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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Considerations for Source-Specific Multicast  . . . . . . . .   3
   3.  Updated Dynamic Multicast Group IDs . . . . . . . . . . . . .   3
   4.  Operational Considerations  . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   For IPv6 multicast addresses, Section 2 of [RFC3307] defines the
   lower 32 bits of the IPv6 address, which are mapped directly to the
   link-layer, as the group ID, and then assigns ranges of group ID
   values based on how they are allocated.  Section 4.3 of [RFC3307]
   describes dynamic assignment of group ID values and lists two
   different approaches (server allocation and host allocation).
   However, both approaches are assigned the same range of group ID
   values, which means they cannot coexist without risking an address
   collision.  Also concerning is that the group ID range for dynamic
   assignment overlaps with the range used for Solicited-Node multicast
   addresses (see Section 2.7.1 of [RFC4291] for definition of this
   range and [I-D.ietf-pim-zeroconf-mcast-addr-alloc-ps] for discussion
   of problems associated with duplicate group ID values on the
   network).

   Only one server allocation protocol has been defined at the time of
   writing (see [RFC2730]), but
   [I-D.ietf-pim-zeroconf-mcast-addr-alloc-ps] advocates developing a
   decentralized, zero-configuration host allocation protocol.  This
   document updates Section 4.3 of [RFC3307] to allow multiple dynamic
   allocation protocols to coexist on the same network, and so that
   dynamic IPv6 multicast group ID ranges use a registry to better align
   with current practices for protocol number assignment.

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   This document adheres to the IPv6 multicast address architecture
   outlined in [RFC4291], [RFC3307], [RFC7371], et al.

2.  Considerations for Source-Specific Multicast

   One of the benefits of Source-Specific Multicast (SSM) listed in
   Section 1 of [RFC4607] is "[avoiding] the need for inter-host
   coordination when choosing source-specific addresses".  SSM allows a
   host to subscribe to channel (S,G) and only receive packets for
   destination address G that are from source address S.  This reduces
   the need for coordinated dynamic assignment of G because multiple
   distinct hosts could use the same value for G and traffic would still
   be directed to the node that requested the stream (see [RFC8815],
   Section 3.2.2).

   However, SSM is not universally supported (see [RFC4607], Section 6
   and [RFC8815], Section 3.1).  This document defines a range of
   dynamic IPv6 multicast group IDs for use in environments that do
   support SSM.

3.  Updated Dynamic Multicast Group IDs

   Existing group ID allocations specified in [RFC3307], Section 4.3 and
   [RFC4291], Section 2.7.1 are summarized in the following table:

   +=======================+================+============+============+
   | Range                 | Solicited-Node |   Server   |    Host    |
   |                       |                | allocation | allocation |
   |                       |                |  (MADCAP)  |            |
   +=======================+================+============+============+
   |                       |                |            |            |
   |                       |                |            |            |
   | 0x80000000-0xFEFFFFFF |       No       |    Yes     |    Yes     |
   |                       |                |            |            |
   |                       |                |            |            |
   +-----------------------+----------------+------------+------------+
   | 0xFF000000-0xFFFFFFFF |      Yes       |    Yes     |    Yes     |
   +-----------------------+----------------+------------+------------+

                      Table 1: Existing Allocations

   This document updates the allocations in [RFC3307], Section 4.3 and
   moves them into a new registry in the IPv6 Multicast Address Space
   registry group.  The registry shall be populated with the following
   entries:

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    +=======================+=================+=======================+
    | Range                 | Description     | Reference             |
    +=======================+=================+=======================+
    | 0x80000000-0x8FFFFFFF | MADCAP          | Defined in [RFC2730], |
    |                       |                 | range assigned in     |
    |                       |                 | [This document]       |
    +-----------------------+-----------------+-----------------------+
    | 0x90000000-0xEFFFFFFF | Unassigned      |                       |
    +-----------------------+-----------------+-----------------------+
    | 0xF0000000-0xFCFFFFFF | Host allocation | [This document]       |
    |                       | of SSM group    |                       |
    |                       | addresses       |                       |
    +-----------------------+-----------------+-----------------------+
    | 0xFD000000-0xFDFFFFFF | Private Use     | [This document]       |
    +-----------------------+-----------------+-----------------------+
    | 0xFE000000-0xFEFFFFFF | Experimental    | [This document]       |
    |                       | Use             |                       |
    +-----------------------+-----------------+-----------------------+
    | 0xFF000000-0xFFFFFFFF | Solicited-Node  | [RFC4291],            |
    |                       | multicast       | Section 2.7.1         |
    |                       | addresses       |                       |
    +-----------------------+-----------------+-----------------------+

                        Table 2: Updated Allocations

   This reduces the range previously available for the Multicast Address
   Dynamic Client Allocation Protocol (MADCAP), while still providing a
   sizable allocation.  It also allocates ranges for SSM, Private Use,
   and Experimental Use. The Private Use range can be used in isolated
   deployments for purposes such as manual address allocation (see
   [RFC8126], Section 4.1).  The Experimental Use range may be used for
   experimentation with new dynamic allocation protocols (see [RFC8126],
   Section 4.2).  There are no restrictions on experimental scope; these
   IDs may be used to run experiments over the open Internet.  Finally,
   this documents the range used for Solicited-Node multicast addresses.
   All remaining entries are reserved for future assignment as new
   protocols are developed.

4.  Operational Considerations

   This document reduces the range of group ID values available for
   MADCAP ([RFC2730]).  At the time of writing, there is only one known
   implementation of MADCAP, and there are no known large-scale
   deployments.  Any implementations of MADCAP (known or otherwise)
   should be updated to reflect the new group ID range set forth in
   Table 2.  Any existing deployments of MADCAP should either use an
   updated implementation or operate in an environment without other
   IPv6 multicast address allocation protocols.

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5.  Security Considerations

   This document does not expand on any security considerations beyond
   what is discussed in [RFC3307] and [RFC2908].

6.  IANA Considerations

   This document requests IANA create a new registry named "Dynamic
   Multicast Group IDs" in the "IPv6 Multicast Address Space" registry
   group.  The "Standards Action" registration policy is required to
   update the registry.  Each entry in the registry contains the
   following fields:

   1.  Range
       A range of 32-bit values rendered in hexadecimal.  Values must be
       within the range 0x80000000 to 0xFFFFFFFF.

   2.  Description
       A description or protocol name assigned to the range.

   3.  Reference
       A document describing the assignment.

   The registry shall initially contain the entries listed in Table 2,
   and shall list both [RFC3307] and this document as references.

   IANA should also update the references to
   "FF3X:0:0:0:0:0:8000:0-FF3X:0:0:0:0:0:FFFF:FFFF" in the "Unicast-
   based (Including SSM) Multicast Group IDs" registry in the "IPv6
   Multicast Address Space" registry group.  The registration procedure
   should indicate that this range uses dynamic assignment according to
   the protocols listed in the new "Dynamic Multicast Group IDs"
   registry and include a reference to this document.  The description
   in the registry entry should indicate that this range uses dynamic
   assignment according to the protocols listed in the new "Dynamic
   Multicast Group IDs" registry and the reference should be changed to
   this document.

7.  Acknowledgement

   Special thanks to the National Marine Electronics Association for
   their contributions in developing marine industry standards and their
   support for this work.

   The authors are grateful to the members of the PIM working group for
   their early brainstorming sessions and review of this document, and
   to the following individuals specifically:

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   *  Dave Thaler for discussing MADCAP deployment in Microsoft products
      and the impact of changing the range of group IDs used by MADCAP

   *  Stig Venaas for recognizing the need for a range of addresses that
      can be allocated manually

   *  Nico Cvitak for recommending a group ID block for SSM

8.  References

8.1.  Normative References

   [RFC2730]  Hanna, S., Patel, B., and M. Shah, "Multicast Address
              Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
              DOI 10.17487/RFC2730, December 1999,
              <https://www.rfc-editor.org/info/rfc2730>.

   [RFC3307]  Haberman, B., "Allocation Guidelines for IPv6 Multicast
              Addresses", RFC 3307, DOI 10.17487/RFC3307, August 2002,
              <https://www.rfc-editor.org/info/rfc3307>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
              <https://www.rfc-editor.org/info/rfc4607>.

8.2.  Informative References

   [I-D.ietf-pim-zeroconf-mcast-addr-alloc-ps]
              Karstens, N., Farinacci, D., and M. McBride, "Zeroconf
              Multicast Address Allocation Problem Statement and
              Requirements", Work in Progress, Internet-Draft, draft-
              ietf-pim-zeroconf-mcast-addr-alloc-ps-13, 17 February
              2026, <https://datatracker.ietf.org/doc/html/draft-ietf-
              pim-zeroconf-mcast-addr-alloc-ps-13>.

   [RFC2908]  Thaler, D., Handley, M., and D. Estrin, "The Internet
              Multicast Address Allocation Architecture", RFC 2908,
              DOI 10.17487/RFC2908, September 2000,
              <https://www.rfc-editor.org/info/rfc2908>.

   [RFC7371]  Boucadair, M. and S. Venaas, "Updates to the IPv6
              Multicast Addressing Architecture", RFC 7371,
              DOI 10.17487/RFC7371, September 2014,
              <https://www.rfc-editor.org/info/rfc7371>.

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   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8815]  Abrahamsson, M., Chown, T., Giuliano, L., and T. Eckert,
              "Deprecating Any-Source Multicast (ASM) for Interdomain
              Multicast", BCP 229, RFC 8815, DOI 10.17487/RFC8815,
              August 2020, <https://www.rfc-editor.org/info/rfc8815>.

Authors' Addresses

   Nate Karstens
   Garmin International, Inc.
   1200 E. 151st St.
   Olathe, KS 66062-3426
   United States of America
   Email: nate.karstens@gmail.com

   Dino Farinacci
   lispers.net
   San Jose, CA
   United States of America
   Email: farinacci@gmail.com

   Mike McBride
   Futurewei
   United States of America
   Email: michael.mcbride@futurewei.com

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