IGMP multicasting

IGMP identifies members of a multicast group within a subnet and lets IGMP-configured hosts and routers join or leave multicast groups based on the following:

  • An IP multicast packet includes the multicast group address to which the packet belongs.

  • When an IGMP client connected to a switch port needs to receive multicast traffic from a specific group, it joins the group by sending an IGMP report (join request) to the network. The multicast group specified in the join request is determined by the requesting application running on the IGMP client.

  • When a networking device with IGMP enabled receives the join request for a specific group, it forwards any IP multicast traffic it receives for that group through the port on which the join request was received.

  • When the client is ready to leave the multicast group, it sends a Leave Group message to the network and ceases to be a group member.

  • When the leave request is detected, the appropriate IGMP device ceases to transmit traffic for the designated multicast group through the port on which the leave request was received, as long as there are no other current members of that group on the affected port.