Internet Group Management Protocol, Version 2
RFC 2236
Document | Type |
RFC - Proposed Standard
(November 1997; Errata)
Updated by RFC 3376
Updates RFC 1112
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|
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Author | Bill Fenner | ||
Last updated | 2020-01-21 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized with errata bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 2236 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group W. Fenner Request for Comments: 2236 Xerox PARC Updates: 1112 November 1997 Category: Standards Track Internet Group Management Protocol, Version 2 Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1997). All Rights Reserved. Abstract This memo documents IGMPv2, used by IP hosts to report their multicast group memberships to routers. It updates STD 5, RFC 1112. IGMPv2 allows group membership termination to be quickly reported to the routing protocol, which is important for high-bandwidth multicast groups and/or subnets with highly volatile group membership. This document is a product of the Inter-Domain Multicast Routing working group within the Internet Engineering Task Force. Comments are solicited and should be addressed to the working group's mailing list at idmr@cs.ucl.ac.uk and/or the author(s). 1. Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC 2119]. 2. Introduction The Internet Group Management Protocol (IGMP) is used by IP hosts to report their multicast group memberships to any immediately- neighboring multicast routers. This memo describes only the use of IGMP between hosts and routers to determine group membership. Routers that are members of multicast groups are expected to behave Fenner Standards Track [Page 1] RFC 2236 Internet Group Management Protocol November 1997 as hosts as well as routers, and may even respond to their own queries. IGMP may also be used between routers, but such use is not specified here. Like ICMP, IGMP is a integral part of IP. It is required to be implemented by all hosts wishing to receive IP multicasts. IGMP messages are encapsulated in IP datagrams, with an IP protocol number of 2. All IGMP messages described in this document are sent with IP TTL 1, and contain the IP Router Alert option [RFC 2113] in their IP header. All IGMP messages of concern to hosts have the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Max Resp Time | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.1. Type There are three types of IGMP messages of concern to the host- router interaction: 0x11 = Membership Query There are two sub-types of Membership Query messages: - General Query, used to learn which groups have members on an attached network. - Group-Specific Query, used to learn if a particular group has any members on an attached network. These two messages are differentiated by the Group Address, as described in section 1.4 . Membership Query messages are referred to simply as "Query" messages. 0x16 = Version 2 Membership Report 0x17 = Leave Group There is an additional type of message, for backwards-compatibility with IGMPv1: 0x12 = Version 1 Membership Report Fenner Standards Track [Page 2] RFC 2236 Internet Group Management Protocol November 1997 This document refers to Membership Reports simply as "Reports". When no version is specified, the statement applies equally to both versions. Unrecognized message types should be silently ignored. New message types may be used by newer versions of IGMP, by multicast routing protocols, or other uses. 2.2. Max Response Time The Max Response Time field is meaningful only in Membership Query messages, and specifies the maximum allowed time before sending a responding report in units of 1/10 second. In all other messages, it is set to zero by the sender and ignored by receivers. Varying this setting allows IGMPv2 routers to tune the "leave latency" (the time between the moment the last host leaves a group and when the routing protocol is notified that there are no more members), as discussed in section 7.8. It also allows tuning of theShow full document text