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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-07
Chapter 21 Configuring IGMP Snooping and MVR
Configuring IGMP Snooping
Beginning in privileged EXEC mode, follow these steps to configure the TCN flood query count:
To return to the default flooding query count, use the
no ip igmp snooping tcn
flood query count
global
configuration command.
Recovering from Flood Mode
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, when you enable the
ip igmp
snooping tcn query solicit
global configuration command, the switch sends the global leave message
whether or not it is the spanning-tree root. 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 switch is the spanning-tree root regardless of this configuration
command. By default, query solicitation is disabled.
Beginning in privileged EXEC mode, follow these steps to enable the switch sends the global leave
message whether or not it is the spanning-tree root:
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 two general queries are
received. If the switch has many ports with attached hosts that are subscribed to different multicast
groups, the 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.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
ip igmp snooping tcn
flood query count
count
Specify the number of IGMP general queries for which the multicast
traffic is flooded. The range is 1 to 10. By default, the flooding query
count is 2.
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.
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.
Содержание ME 3400 Series
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