Allied Telesis AT-S60 - Manual (Page 220)

Chapter 14: IGMP Snooping
Section II: Advanced Features 220
IGMP snooping enables the Fast Ethernet switch to monitor the flow of
queries from a router and reports from host nodes to build its own
multicast membership lists. The switch uses the lists to forward multicast
packets only to switch ports where there are host nodes that are
members of multicast groups. This improves switch performance and
network security by restricting the flow of multicast packets only to
those switch ports connected to host nodes.
Without IGMP snooping, a switch would flood multicast packets from all
of its ports, except the port on which it received the packet. Such
flooding of packets can negatively impact switch and network
performance.
The AT-8400 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
The default setting for IGMP snooping is disabled.