Internet Engineering Task Force (IETF) N. Karstens
Request for Comments: 10028 Garmin
Updates: 3307 D. Farinacci
Category: Standards Track lispers.net
ISSN: 2070-1721 M. McBride
Futurewei
August 2026
Updates to Dynamic IPv6 Multicast Address Group IDs
Abstract
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This document describes limitations of the existing range of dynamic IPv6 multicast addresses specified in "Allocation Guidelines for IPv6 Multicast Addresses" (RFC 3307). It updates RFC 3307 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) (RFC 2730), a range for Source-Specific Multicast (SSM), a Private Use range, a range for Experimental Use, and Solicited-Node multicast addresses (which were not previously noted in RFC 3307).
Status of This Memo
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This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc10028.
Copyright Notice
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Copyright © 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 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
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1. Introduction 2. Considerations for Source-Specific Multicast 3. Updated Dynamic Multicast Group IDs 4. Operational Considerations 5. Security Considerations 6. IANA Considerations 7. References 7.1. Normative References 7.2. Informative References Acknowledgements Authors' Addresses
1. Introduction
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For IPv6 multicast addresses, [RFC3307], Section 2 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. [RFC3307], Section 4.3 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 [RFC4291], Section 2.7.1 for the definition of this range and [RFC10019] for the 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 [RFC10019] advocates developing a decentralized, zero-configuration host allocation protocol. This document updates [RFC3307], Section 4.3 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.
This document adheres to the IPv6 multicast address architecture outlined in [RFC4291], [RFC3307], [RFC7371], et al.
2. Considerations for Source-Specific Multicast
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One of the benefits of Source-Specific Multicast (SSM) listed in [RFC4607], Section 1 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
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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 the new "Dynamic Multicast Group IDs" registry in the "IPv6 Multicast Address Space" registry group. The registry has been populated with the following entries:
+=======================+=================+=======================+ | Range | Description | Reference | +=======================+=================+=======================+ | 0x80000000-0x8FFFFFFF | MADCAP | Defined in [RFC2730], | | | | range assigned in RFC | | | | 10028 | +-----------------------+-----------------+-----------------------+ | 0x90000000-0xEFFFFFFF | Unassigned | | +-----------------------+-----------------+-----------------------+ | 0xF0000000-0xFCFFFFFF | Host allocation | RFC 10028 | | | of SSM group | | | | addresses | | +-----------------------+-----------------+-----------------------+ | 0xFD000000-0xFDFFFFFF | Reserved for | RFC 10028 | | | Private Use | | +-----------------------+-----------------+-----------------------+ | 0xFE000000-0xFEFFFFFF | Reserved for | RFC 10028 | | | Experimental | | | | Use | | +-----------------------+-----------------+-----------------------+ | 0xFF000000-0xFFFFFFFF | Solicited-Node | [RFC4291], | | | multicast | Section 2.7.1 | | | addresses | | +-----------------------+-----------------+-----------------------+
Table 2: Updated Allocations
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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
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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.
5. Security Considerations
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This document does not expand on any security considerations beyond what is discussed in [RFC3307] and [RFC2908].
6. IANA Considerations
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IANA has created 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:
- Range
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A range of 32-bit values rendered in hexadecimal. Values must be within the range 0x80000000 to 0xFFFFFFFF.
- Description
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A description or protocol name assigned to the range.
- Reference
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A document describing the assignment.
The registry initially contains the entries listed in Table 2 and lists both [RFC3307] and this document as references.
IANA has also updated 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 indicates that this range uses dynamic assignment according to the protocols listed in the new "Dynamic Multicast Group IDs" registry and includes a reference to this document. The description in the registry entry indicates that this range uses dynamic assignment according to the protocols listed in the new "Dynamic Multicast Group IDs" registry and the reference has been changed to this document.
7. References
7.1. Normative References
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[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>.
7.2. Informative References
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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>. [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>. [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>. [RFC10019] Karstens, N., Farinacci, D., and M. McBride, "Zeroconf Multicast Address Allocation Problem Statement and Requirements", RFC 10019, DOI 10.17487/RFC10019, July 2026, <https://www.rfc-editor.org/info/rfc10019>.
Acknowledgements
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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:
- 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
Authors' Addresses
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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.comMike McBride Futurewei United States of America Email: michael.mcbride@futurewei.com