Allied Telesis AT-S25 - Manual (Page 168)

Section II: Local and Telnet Mangement
168
Without IGMP snooping, a switch would have to flood multicast packets
out all of its ports, except the port on which it received the packet. Such
flooding of packets can negatively impact the switch and network
performance.
The AT-8300 Series switch supports both IGMP Version 1 and Version 2.
The switch maintains its 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.