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 (C) The Internet Society (1997). All Rights Reserved.
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 email@example.com and/or the author(s).
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].
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
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
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 |
There are three types of IGMP messages of concern to the host-
0x11 = Membership Query
There are two sub-types of Membership Query messages:
- General Query, used to learn which groups have members on an
- 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
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
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