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AT-9108, AT-8518, AT-8525, and AT-8550 User's Guide
IGMP Overview
IGMP is a protocol used by an IP host to register its IP multicast group
membership with a router. Periodically, the router queries the
multicast group to see if the group is still in use. If the group is still
active, a single IP host responds to the query, and group registration
is maintained.
IGMP is enabled by default on the switch. However, the switch can
be configured to disable the generation of period IGMP query
packets. IGMP query should be enabled when the switch is
configured to perform IP unicast or IP multicast routing.
IGMP Snooping. IGMP snooping is a layer-2 function of the switch.
It does not require multicast routing to be enabled. The feature
reduces the flooding of IP multicast traffic. IGMP snooping optimizes
the usage of network bandwidth, and prevents multicast traffic from
being flooded to parts of the network that do not need it. The switch
does not reduce any IP multicast traffic in the local multicast domain
(224.0.0.x).
IGMP snooping is enabled by default on the switch. If you are using
multicast routing, IGMP snooping must be enabled. If IGMP
snooping is disabled, all IGMP and IP multicast traffic floods within a
given VLAN. IGMP snooping expects at least one device in the
network to periodically generate IGMP query messages. Without an
IGMP querier, the switch stops forwarding IP multicast packets to any
port. An optional optimization for IGMP snooping is the strict
recognition of multicast routers only if the remote devices has joined
the DVMRP (224.0.0.4) or PIM (244.0.0.13) multicast groups.
IGMP configuration commands can be found in
Table
10-2.
10-3
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