Disabling Multicast Flooding During A Tcn Event; Configuring The Igmp Snooping Querier - Cisco WS-C3020 Software Configuration Manual

Configuring IGMP Snooping

Disabling Multicast Flooding During a TCN Event

When the switch receives a TCN, multicast traffic is flooded to all the ports until 2 general queries are
received. If the switch has many ports with attached hosts that are subscribed to different multicast
groups, this flooding might exceed the capacity of the link and cause packet loss. You can use the ip
igmp snooping tcn flood interface configuration command to control this behavior.
Beginning in privileged EXEC mode, follow these steps to disable multicast flooding on an interface:
Command
Step 1 configure terminal
Step 2 interface interface-id
Step 3
no ip igmp snooping tcn flood
Step 4
exit
Step 5 show ip igmp snooping
Step 6 copy running-config startup-config
To re-enable multicast flooding on an interface, use the ip igmp snooping tcn flood interface
configuration command.

Configuring the IGMP Snooping Querier

Follow these guidelines when configuring the IGMP snooping querier:
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Configure the VLAN in global configuration mode.
Configure an IP address on the VLAN interface. When enabled, the IGMP snooping querier uses the
IP address as the query source address.
If there is no IP address configured on the VLAN interface, the IGMP snooping querier tries to use
the configured global IP address for the IGMP querier. If there is no global IP address specified, the
IGMP querier tries to use the VLAN switch virtual interface (SVI) IP address (if one exists). If there
is no SVI IP address, the switch uses the first available IP address configured on the switch. The first
IP address available appears in the output of the show ip interface privileged EXEC command. The
IGMP snooping querier does not generate an IGMP general query if it cannot find an available IP
address on the switch.
The IGMP snooping querier supports IGMP Versions 1 and 2.
When administratively enabled, the IGMP snooping querier moves to the nonquerier state if it
detects the presence of a multicast router in the network.
When it is administratively enabled, the IGMP snooping querier moves to the operationally disabled
state under these conditions:
IGMP snooping is disabled in the VLAN.
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PIM is enabled on the SVI of the corresponding VLAN.
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Purpose
Enter global configuration mode.
Specify the interface to be configured, and enter interface
configuration mode.
Disable the flooding of multicast traffic during a spanning-tree TCN
event.
By default, multicast flooding is enabled on an interface.
Return to privileged EXEC mode.
Verify the TCN settings.
(Optional) Save your entries in the configuration file.
Chapter 22 Configuring IGMP Snooping and MVR
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