Internet Group Management protocol (IGMP) is a group management protocol.

IGMP is not a multicasting routing protocol; it is a protocol that manages group membership. In any network, there are one or more multicast routers that distribute multicast packets to hosts or other routers.

IGMP message types are as follows:

Fig.2 shows IGMP message format.

1. Type : It defines the type of message.

IGMP type field

2. Maximum response time : It defined the amount of time in which a query must be answered.

3. Checksum : This is 16 bit field carrying the checksum. The checksum is calculated over the 8 byte message.

4. Group address : For general query message value is zero. The value defines the groupid in the special query, the membership report and the leave report messages.

• Hosts respond to a membership query message with an IGMP membership report message, which is shown in Fig.3.
• Membership report messages are received by the router, as well as all hosts on the attached interface. Each membership report contains the multicast address of a single group that the responding host has joined.
• When a host sees that no process is interested in a specific group, it sends a leave report. Also when router sees that none of the networks connected to its interfaces is interested in a specific group, it sends a leave report about that group.