IGMP
Internet Group Management Protocol (IGMP) is used to dynamically register individual hosts in a multicast group on a particular LAN. Hosts identify group memberships by sending IGMP messages to their local multicast router. Under IGMP, routers listen to IGMP messages and periodically send out queries to discover which groups are active or inactive on a particular subnet.
RFC 2236 defines the specification for IGMP Version 2. There are four types of IGMP messages:
_ Membership query
_ IGMP Version 1 membership report _ IGMP Version 2 membership report _ Leave group
Hosts send out IGMP membership reports corresponding to a particular multicast group to indicate that they are interested in joining that group. The router periodically sends out an IGMP membership query to verify that at least one host on the subnet is still interested in receiving traffic directed to that group. When there is no reply to three consecutive IGMP membership queries, the router times out the group and stops forwarding traffic directed toward that group.
With leave group message, the hosts can actively communicate to the local multicast router their intention to leave the group. The router then sends out a
