Cisco Systems 3750E manual Disabling Multicast Flooding During a TCN Event, 24-14

Chapter 24 Configuring IGMP Snooping and MVR

Configuring IGMP Snooping

Beginning in privileged EXEC mode, follow these steps to enable the switch to send the global leave message whether or not it is the spanning-tree root:

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	ip igmp snooping tcn query solicit	Send an IGMP leave message (global leave) to speed the process of
		recovering from the flood mode caused during a TCN event. By
		default, query solicitation is disabled.
Step 3
	end	Return to privileged EXEC mode.
Step 4
	show ip igmp snooping	Verify the TCN settings.
Step 5
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return to the default query solicitation, use the no ip igmp snooping tcn query solicit global configuration command.

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	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	interface interface-id	Specify the interface to be configured, and enter interface
		configuration mode.
Step 3
	no ip igmp snooping tcn flood	Disable the flooding of multicast traffic during a spanning-tree TCN
		event.
		By default, multicast flooding is enabled on an interface.
Step 4
	exit	Return to privileged EXEC mode.
Step 5
	show ip igmp snooping	Verify the TCN settings.
Step 6
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To re-enable multicast flooding on an interface, use the ip igmp snooping tcn flood interface configuration command.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
24-14	OL-9775-02