| RFC 9778 | IANA Considerations for IGMP | March 2025 |
| Haberman | Best Current Practice | [Page] |
This document specifies revised IANA considerations for the Internet Group Management Protocol (IGMP) and the Multicast Listener Discovery (MLD) protocol. This document specifies the guidance provided to IANA to manage values associated with various fields within the protocol headers of the group management protocols.¶
This document obsoletes RFC 3228 and unifies guidelines for IPv4 and IPv6 group management protocols.¶
This memo documents an Internet Best Current Practice.¶
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 BCPs 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/rfc9778.¶
Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.¶
The sections that follow describe the allocation guidelines associated with the specified fields within the Internet Group Management Protocol (IGMP) [RFC9776] and the Multicast Listener Discovery (MLD) [RFC9777] headers. Some of these registries were created previously, while others are created by this document.¶
This document obsoletes [RFC3228] and unifies guidelines for IPv4 and IPv6 group management protocols.¶
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.¶
The registration procedures used in this document are defined in [RFC8126].¶
The IGMP header contains the following fields that carry values assigned from IANA-managed name spaces: Type and Code. Code field values are defined relative to a specific Type value.¶
[RFC3228] created the "IGMP Type Numbers" registry for the IGMP Type field. This document updates that registry in two ways:¶
[RFC3228] created the '"Code" Fields' registry for Code values for existing IGMP Type fields. This document updates that registry in two ways:¶
Note that the policy for assigning Code values for new IGMP Types MUST be defined in the document defining the new Type value.¶
As with IGMP, the MLD header also contains Type and Code fields. Assignment of those fields within the MLD header is defined in [RFC4443] with a registration policy of IETF Review.¶
IANA has created the "IGMP/MLD Query Message Flags" registry for the bits in the Flags field of the MLDv2 Query Message [RFC9777] and the IGMPv3 Query Message [RFC9776]. It has been populated as follows:¶
| Flags Bit | Short Name | Description | Reference |
|---|---|---|---|
| 0 | E | Extension | [RFC9279] |
| 1-3 | Unassigned | ||
The Flags Bit value in the registry above corresponds to the column header in the packet format diagrams in [RFC9777] and [RFC9776].¶
The initial contents of this registry contain the E-bit defined in [RFC9279].¶
The assignment of new bit flags within the Flags field requires Standards Action.¶
IANA has created the "IGMP/MLD Report Message Flags" registry for the bits in the Flags field of the MLDv2 Report Message and the IGMPv3 Report Message. It has been populated as follows:¶
| Flags Bit | Short Name | Description | Reference |
|---|---|---|---|
| 0 | E | Extension | [RFC9279] |
| 1-15 | Unassigned | ||
The Flags Bit value in the registry above corresponds to the column header in the packet format diagrams in [RFC9777] and [RFC9776].¶
The initial contents of this registry includes the E-bit defined in [RFC9279].¶
The assignment of new bit flags within the Flags field requires Standards Action.¶
Security analyzers such as firewalls and network intrusion detection monitors often rely on unambiguous interpretations of the fields described in this memo. As new values for the fields are assigned, existing security analyzers that do not understand the new values may fail, resulting in either loss of connectivity if the analyzer declines to forward the unrecognized traffic or loss of security if it does forward the traffic and the new values are used as part of an attack. This vulnerability argues for high visibility (which the Standards Action process ensures) for the assignments whenever possible.¶
Bill Fenner is the author of [RFC3228], which provided a portion of the content contained herein.¶