Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 362)

Switching Introduction
Software Reference for x310 Series Switches
14.20 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
IGMP Snooping
IGMP (Internet Group Management Protocol) is used by IP hosts to report their multicast
group memberships to routers and switches. IP hosts join a multicast group to receive
broadcast messages directed to the multicast group address. IGMP is an IP-based protocol
and uses IP addresses to identify both the multicast groups and the host members. For a
VLAN-aware devices, this means multicast group membership is on a per-VLAN basis. If at
least one port in the VLAN is a member of a multicast group, by default multicast packets
will be flooded onto all ports in the VLAN.
IGMP snooping enables the switch to forward multicast traffic intelligently on the switch.
The switch listens to IGMP membership reports, queries and leave messages to identify
the switch ports that are members of multicast groups. Multicast traffic will only be
forwarded to ports identified as members of the specific multicast group.
IGMP snooping is performed at Layer 2 on VLAN interfaces automatically. By default, the
switch will forward traffic only from those ports with multicast listeners, therefore it will
not act as a simple hub and flood all multicast traffic out all ports. IGMP snooping is
independent of the IGMP and Layer 3 configuration, so an IP interface does not have to be
attached to the VLAN, and IGMP does not have to be enabled or configured.
IGMP snooping is enabled by default.
For more information on IGMP see Chapter 30, IGMP and IGMP Snooping Introduction
and Chapter 31, IGMP Snooping Commands .