Allied Telesis AT-S63 - Manual (Page 235)

AT-S63 Management Software Menus Interface User’s Guide
Section II: Advanced Features 235
Without IGMP snooping a switch would be obligated 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 switch and
network performance.
The AT-9400 Series switch maintains its list of multicast groups through
an adjustable timeout 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.