Internet Group Management Protocol (IGMP)

IGMP is used for IP multicast. A multicast is communication between a single sender and multiple receivers on a network. IGMP is used to exchange membership status data between IP routers that support multicasting and members of multicast groups. A router is an intermediary device on a communication network that expedites message delivery by finding the most efficient route for a message packet within a network, or by routing packets from one subnetwork to another. A subnetwork is a separate part of an organization's network identified through IP addressing.

Host membership in a multicast group is reported by individual member hosts and membership status is periodically polled by multicast routers. Multicast addresses are reserved from within a standard specified range of all IP addresses to enable forwarding across routers configured to permit multicasting.

IP provides a mechanism to send and receive multicast IP traffic. Multicast IP traffic is sent to a single media access control address, but is processed by multiple IP hosts. A specified host listens on a specific IP multicast address and receives all packets on that address. This requires IP multicast support on the IP routers and the ability for hosts to register themselves with the router. Host registration is accomplished using IGMP.

For IP multicasting to span routers across networks, a protocol is required to inform routers that hosts of a specific multicast group are available on a specified network. This data is passed among routers through the use of multicast routing protocols. These protocols ensure that each router that supports the forwarding of multicasts is aware of which host groups are on which network.

Windows CE provides level 2 (full) support for IP multicasting (IGMP version 2) as described in RFC 1112 and RFC 2236.

 Last updated on Friday, April 02, 2004

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