RFC 2236 (rfc2236) - Page 2 of 24
Internet Group Management Protocol, Version 2
Alternative Format: Original Text Document
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
