Recovering From Flood Mode (Cli) - Cisco Catalyst 3850 series Configuration Manual

How to Configure IGMP Snooping
Command or Action
Step 2
configure terminal
Example:
Device# configure terminal
Step 3 ip igmp snooping tcn flood query count count
Example:
Device(config)# ip igmp snooping tcn flood
query count 3
Step 4 end
Example:
Device(config)# end
Step 5
show ip igmp snooping
Example:
Device# show ip igmp snooping
Step 6
copy running-config startup-config
Example:
Device# copy running-config startup-config

Recovering from Flood Mode (CLI)

When a topology change occurs, the spanning-tree root sends a special IGMP leave message (also known as
global leave) with the group multicast address 0.0.0.0. However, you can enable the device to send the global
leave message whether it is the spanning-tree root or not. When the router receives this special leave, it
immediately sends general queries, which expedite the process of recovering from the flood mode during the
TCN event. Leaves are always sent if the device is the spanning-tree root regardless of this configuration.
Follow these steps to enable sending of leave messages:
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
84
Purpose
Enters the global configuration mode.
Specifies the number of IGMP general queries for which the
multicast traffic is flooded.
The range is 1 to 10. The default, the flooding query count is
2.
To return to the default flooding query count, use the
Note
no ip igmp snooping tcn flood query count global
configuration command.
Returns to privileged EXEC mode.
Verifies the TCN settings.
(Optional) Saves your entries in the configuration file.
Configuring IGMP
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