Updates to Dynamic IPv6 Multicast Address Group IDs
draft-ietf-pim-updt-ipv6-dyn-mcast-addr-grp-id-11

Network Working Group                                        N. Karstens
Internet-Draft                                                    Garmin
Updates: 3307 (if approved)                                 D. Farinacci
Intended status: Standards Track                             lispers.net
Expires: 30 August 2026                                       M. McBride
                                                               Futurewei
                                                        26 February 2026

          Updates to Dynamic IPv6 Multicast Address Group IDs
           draft-ietf-pim-updt-ipv6-dyn-mcast-addr-grp-id-11

Abstract

   This document describes limitations of the existing range of dynamic
   IPv6 multicast addresses specified in RFC3307.  It recommends
   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 MADCAP
   (RFC2730), a range for SSM, a Private Use range, and Solicited-Node
   multicast addresses (which were not previously noted in RFC3307,
   Allocation Guidelines for IPv6 Multicast Addresses).

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 30 August 2026.

Copyright Notice

   Copyright (c) 2026 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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   license-info) in effect on the date of publication of this document.

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   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 range for dynamic assignment
   overlaps with the range used for Solicited-Node multicast addresses
   (see Section 2.7.1 of [RFC4291]).

   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] so that dynamic IPv6
   multicast group ID ranges better align with current practices for
   protocol number assignment and additional dynamic allocation
   protocols may be developed.

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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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

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   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:

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

                        Table 2: Updated Allocations

   This reduces the range previously available for MADCAP, while still
   providing a sizable allocation.  It also allocates ranges for SSM and
   for Private Use. The Private Use range can be used in isolated
   deployments for purposes such as manual address allocation or
   experimentation with new dynamic allocation protocols.  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

   [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>.

   [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>.

   [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>.

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-11, 12 February
              2026, <https://datatracker.ietf.org/doc/html/draft-ietf-
              pim-zeroconf-mcast-addr-alloc-ps-11>.

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   [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>.

   [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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