What is IGMP Snooping in the TCSESM Ethernet managed switches?

By default, a switch treats multicast traffic like broadcast traffic: it floods every multicast frame out to all ports, whether or not a device on that port actually wants it. On a network carrying industrial multicast traffic (e.g., producer/consumer I/O data), this wastes bandwidth and forces every connected device to process frames it will just discard.

IGMP (Internet Group Management Protocol) snooping fixes this. The switch listens in on the IGMP join/leave messages that hosts and routers exchange to manage multicast group membership, and builds a table of which ports have subscribed to which multicast groups. It then forwards each multicast stream only out the ports that actually asked for it — pruning it from every other port.

Multicast traffic reaches only the devices that need it, cutting unnecessary load on the switch and on hosts that aren't part of the group.