RFC 9778: IANA Considerations for Internet Group Management Protocols
Author: Brian Haberman
Description: 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.

RFC 9778 | IANA Considerations for IGMP | March 2025
Haberman | Best Current Practice | [Page]

Stream:
  Internet Engineering Task Force (IETF)
RFC:
  9778
BCP:
  57
Obsoletes:
  3228
Category:
  Best Current Practice
Published:
  March 2025
ISSN:
  2070-1721
Author:
  B. Haberman, Ed.
  JHU APL

# RFC 9778

# IANA Considerations for Internet Group Management Protocols

## Abstract

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.¶

## Status of This Memo

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 Notice

Copyright (c) 2025 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.¶

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.¶

## 1. Introduction

The sections that follow describe the allocation guidelines associated with the specified fields within the Internet Group Management Protocol (IGMP) [STD100] and the Multicast Listener Discovery (MLD) [STD101] 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.¶

### 1.1. Conventions Used in This Document

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. IANA Considerations

The registration procedures used in this document are defined in [RFC8126].¶

### 2.1. Type and Code Fields

#### 2.1.1. Internet Group Management Protocol

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:¶

- The registration procedure has been changed to Standards Action.¶
- The references to [RFC3228], including the reference for the registry, have been changed to this document.¶

[RFC3228] created the '"Code" Fields' registry for Code values for existing IGMP Type fields. This document updates that registry in two ways:¶

- The registration procedure has been changed to Standards Action.¶
- The reference for the registry has been changed to this document.¶

Note that the policy for assigning Code values for new IGMP Types MUST be defined in the document defining the new Type value.¶

#### 2.1.2. Multicast Listener Discovery

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; see <https://www.iana.org/assignments/icmpv6-parameters>.¶

### 2.2. IGMP/MLD Query Message Flags

IANA has created the "IGMP/MLD Query Message Flags" registry for the bits in the Flags field of the MLDv2 Query Message [STD101] and the IGMPv3 Query Message [STD100]. It has been populated as follows:¶

Table 1: IGMP/MLD Query Message Flags Registry
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 Sections 4.1 and 4.2 of [STD100] and Sections 5.1 and 5.2 of [STD101].¶

The assignment of new bit flags within the Flags field requires Standards Action.¶

### 2.3. IGMP/MLD Report Message Flags

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:¶

Table 2: IGMP/MLD Report Message Flags Registry
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 [STD101] and [STD100].¶

The assignment of new bit flags within the Flags field requires Standards Action.¶

## 3. Security Considerations

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.¶

## 4. References

### 4.1. 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>.
[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>.
[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>.
[STD100]
  Internet Standard 100, <https://www.rfc-editor.org/info/std100>.
  At the time of writing, this STD comprises the following:
  Haberman, B., Ed., "Internet Group Management Protocol, Version 3", STD 100, RFC 9776, DOI 10.17487/RFC9776, March 2025, <https://www.rfc-editor.org/info/rfc9776>.
[STD101]
  Internet Standard 101, <https://www.rfc-editor.org/info/std101>.
  At the time of writing, this STD comprises the following:
  Haberman, B., Ed., "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", STD 101, RFC 9777, DOI 10.17487/RFC9777, March 2025, <https://www.rfc-editor.org/info/rfc9777>.

### 4.2. Informative References

[RFC3228]
  Fenner, B., "IANA Considerations for IPv4 Internet Group Management Protocol (IGMP)", BCP 57, RFC 3228, DOI 10.17487/RFC3228, February 2002, <https://www.rfc-editor.org/info/rfc3228>.
[RFC4443]
  Conta, A., Deering, S., and M. Gupta, Ed., "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", STD 89, RFC 4443, DOI 10.17487/RFC4443, March 2006, <https://www.rfc-editor.org/info/rfc4443>.
[RFC9279]
  Sivakumar, M., Venaas, S., Zhang, Z., and H. Asaeda, "Internet Group Management Protocol Version 3 (IGMPv3) and Multicast Listener Discovery Version 2 (MLDv2) Message Extension", RFC 9279, DOI 10.17487/RFC9279, August 2022, <https://www.rfc-editor.org/info/rfc9279>.

## Contributors

Bill Fenner is the author of [RFC3228], which provided a portion of the content contained herein.¶

## Author's Address