Internet Group Management Protocol (IGMP) is used between hosts and their local multicast router. IGMP messages are encapsulated by IP and use the IP protocol number 0x02.
There are two versions of IGMP:
IGMP version 1 is supported by TCP/IP for Windows NT version 4.0 Service Pack 3 and earlier and Microsoft® Windows® 95.
IGMP version 2 is supported by TCP/IP for Microsoft Windows NT 4.0 Service Pack 4 and later, Microsoft® Windows® 98, and Windows 2000.
IGMP version 2 is backward compatible with IGMP version 1. The differences between the two versions are discussed in the following sections.
IGMP is only used to maintain host group membership on a local subnet. IP multicast traffic is not sent using an IGMP header. Typical IP multicast traffic uses a User Datagram Protocol (UDP) header.