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IGMP – Internet Group Management Protocol

IGMP is an extension of the IP protocol and must be implemented by the IP module. IGMP is used by multicast applications. When sending a broadcast message on a local network, each node of this network analyzes the message up to the transport layer to check if any application wants to receive messages from the broadcast port. If there are no pending applications, the message is destroyed and is not transmitted above the transport layer. This means that each host needs to spend several cycles of the central processor (CPU), regardless of whether it is interested in broadcasting or not.

For group distribution, this point is taken into account, and messages are not sent to all nodes on the local network, but only to a group of nodes. The network interface card can determine if the system is interested in this message by analyzing the broadcast MAC address and not using the CPU.

Interest in multicast messages is registered by sending a request for group membership through an IGMP message. Similarly, you can use IGMP to opt out of membership.