# Internet Group Management Protocol and how it works

Internet Group Management Protocol (IGMP) is an integral part of Internet Protocol.

The IGMP messages are encapsulated in IP datagrams. IGMP is used both between hosts and multicast routers, and between multicast routers. It keeps multicast routers informed of the multicast group memberships on a given local network. Each host supporting multicasting must join the multicast group with the address 224.0.0.1 on each network interface at the initialization time. They shall remain members of this group as long as they are active. With IGMP, the hosts on a LAN can inform the routers that they want to be able to receive multicast messages from external networks.