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
