4.4.9 IGMP/MLD Snooping
The Internet Group Management Protocol (IGMP) is a communications protocol used to manage
the membership of Internet Protocol multicast groups. IGMP is used by IP hosts and adjacent
multicast routers to establish multicast group memberships. It can be used more efficiently when
supporting activities, such as online streaming video and gaming.
IGMP Snooping is the process of listening to IGMP traffic. IGMP snooping, as implied by the name,
is a feature that allows the switch to “listen in” on the IGMP conversation between hosts and
routers by processing the layer 3 packets that IGMP packets sent in a multicast network.
When IGMP snooping is enabled in a switch, it analyses all the IGMP packets between hosts
connected to the switch and multicast routers in the network. When a switch receives an IGMP
report for a given multicast group from a host, the switch adds the host's port number to the
multicast list for that group. When the switch hears an IGMP Leave, it removes the host's port from
the table entry.
IGMP snooping can reduce multicast traffic from streaming and make other bandwidth intensive IP
applications run more effectively. A switch using IGMP snooping will only forward multicast traffic
to the hosts in that traffic. This reduction of multicast traffic reduces the packet processing at the
switch (at the cost of needing additional memory to handle the multicast tables) and also
decreases the workload at the end hosts since their network cards (or operating system) will not
receive and filter all the multicast traffic generated in the network.
Multicast Listener Discovery (MLD) is a component of the Internet Protocol Version 6 (IPv6) suite.
MLD is used by IPv6 routers for discovering multicast listeners on a directly attached link, much
like IGMP is used in IPv4.
Select the folder IGMP/MLD Snooping from the Switch Management menu and then five options
within this folder will be displayed.
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