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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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 10 September 2026. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. Karstens, et al. Expires 10 September 2026 [Page 1] Internet-Draft Dynamic IPv6 Mcast Addr Group ID Updates March 2026 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 and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are 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. Karstens, et al. Expires 10 September 2026 [Page 2] Internet-Draft Dynamic IPv6 Mcast Addr Group ID Updates March 2026 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: Karstens, et al. Expires 10 September 2026 [Page 3] Internet-Draft Dynamic IPv6 Mcast Addr Group ID Updates March 2026 +=======================+=================+=======================+ | 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. Karstens, et al. Expires 10 September 2026 [Page 4] Internet-Draft Dynamic IPv6 Mcast Addr Group ID Updates March 2026 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: Karstens, et al. Expires 10 September 2026 [Page 5] Internet-Draft Dynamic IPv6 Mcast Addr Group ID Updates March 2026 * 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, . [RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast Addresses", RFC 3307, DOI 10.17487/RFC3307, August 2002, . [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, . [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, . 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, . [RFC2908] Thaler, D., Handley, M., and D. Estrin, "The Internet Multicast Address Allocation Architecture", RFC 2908, DOI 10.17487/RFC2908, September 2000, . [RFC7371] Boucadair, M. and S. Venaas, "Updates to the IPv6 Multicast Addressing Architecture", RFC 7371, DOI 10.17487/RFC7371, September 2014, . Karstens, et al. Expires 10 September 2026 [Page 6] Internet-Draft Dynamic IPv6 Mcast Addr Group ID Updates March 2026 [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, . [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, . 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 Karstens, et al. Expires 10 September 2026 [Page 7]