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IGMP Snooping
IGMP Snooping is the process of listening to IGMP network traffic. IGMP
Snooping, as implied by the name, is a feature that allows a layer 2 switch to
“listen in” on the IGMP conversation between hosts and routers by
processing the layer3 IGMP packets sent in a multicast network.
When IGMP Snooping is enabled in a switch, it analyzes all IGMP packets
between hosts connected to the switch and multicast routers in the network.
When a switch hears 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.
Moreover, when the switch hears an IGMP Leave, it removes the host’s port
from the table entry.
Prevents flooding of IP multicast traffic, and limits bandwidth intensive video
traffic to only the subscribers.
IGMP Configuration
IGMP Enabled: When enabled, the switch will monitor network traffic to
determine which hosts want to receive multicast traffic.
Router Ports: Set if ports are connecting to the IGMP administrative
routers.
Unregistered IPMC Flooding enabled: Set the forwarding mode for
unregistered (not-joined) IP multicast traffic. The traffic will flood when
enabled, and forward to router-ports only when disabled.
IGMP Snooping Enabled: When enabled, the port will monitor network
traffic to determine which hosts want to receive the multicast traffic.
IGMP Querying Enabled: When enabled, the port can serve as the
Querier
,
which is responsible for asking hosts if they want to receive multicast
traffic.
Figure 2-8
