Allied Telesis AT-GS950/24 - Manual (Page 241)

AT-GS950/24 Web Interface User Guide
241
Without IGMP snooping, a switch floods multicast packets from all of its
ports, except the port on which it received the packet. Such flooding of
packets can negatively impact network performance.
The AT-GS950/24 switch maintains a list of multicast groups through an
adjustable time out value, which controls how frequently it expects to see
reports from end nodes that want to remain members of multicast groups,
and by processing leave requests.
Note
By default, IGMP snooping is disabled on the switch.