Igmp Snooping - Allied Telesis SwitchBlade x908 Series Software Reference Manual

Switching Introduction

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.
Software Reference for SwitchBlade® x908, x900 and x600 Series Switches
TM
C613-50007-01 REV B AlliedWare Plus Operating System - Software Version 5.3.1 14.19