Internet Group Management Protocol (IGMP) snooping allows a switch to forward multicast traffic intelligently. Multicasting is used to support real-time applications such as video conferencing or streaming audio. A multicast server does not have to establish a separate connection with each client. It merely broadcasts its service to the network, and any host that wishes to can receive the multicast register with their local multicast switch.

A multicast group is a group of end nodes that want to receive multicast packets from a multicast application such as a video server delivering content from TV channels. After joining a multicast group, a host node must continue to periodically issue reports to remain a member. Any multicast packets belonging to that multicast group are then forwarded by the switch from the port.

IGMP Snooping checks IGMP packets passing through the network and configures multicasting accordingly. Based on the IGMP query and report messages, the switch forwards traffic only to the ports that request the multicast traffic. The switch can also limit flooding of traffic to IGMP designated ports. This improves network performance by restricting the multicast packets only to switch ports where host nodes are located.

IGMP Snooping significantly reduces overall multicast traffic passing through your switch. Without IGMP snooping, multicast traffic is treated in the same manner as a broadcast transmission, which forwards packets to all ports on the network.