24-Port Managed Gigabit Switch
3.8 IGMP Snooping
3.8.1 IGMP Snooping Introduction
IGMP Snooping is the process of listening to IGMP traffic, which
allows the switch to "listen in" on the IGMP conversation between
hosts and routers by processing the layer 3 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 hearing an IGMP
report from a host for a given multicast group, the switch adds the
host's port number to the multicast list for that group. IGMP
snooping can very effectively reduce multicast traffic from streaming
and other bandwidth intensive IP applications. A switch using IGMP
snooping will only forward multicast traffic to the hosts interested in
that traffic. This reduction of multicast traffic reduces the packet
processing at the switch and also reduces the workload at the end
hosts since their network cards will not have to receive and filter all
the multicast traffic generated in the network. The following figure
compares enabled and disabled state of the IGMP Snooping.
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