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Configuring Optional Spanning-Tree Features
Beginning in privileged EXEC mode, follow these steps to enable root guard on an interface. This
procedure is optional.
Command
Step 1
configure terminal
Step 2
interface interface-id
Step 3
spanning-tree guard root
Step 4
end
Step 5
show running-config
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.
To disable root guard, use the no spanning-tree guard interface configuration command.
Enabling Loop Guard
You can use loop guard to prevent alternate or root ports from becoming designated ports because of a
failure that leads to a unidirectional link. This feature is most effective when it is configured on the entire
switched network. Loop guard operates only on interfaces that are considered point-to-point by the
spanning tree.
You cannot enable both loop guard and root guard at the same time.
Note
You can enable this feature if your switch is running PVST+, rapid PVST+, or MSTP.
Beginning in privileged EXEC mode, follow these steps to enable loop guard. This procedure is optional.
Command
Step 1
show spanning-tree active
or
show spanning-tree mst
Step 2
configure terminal
Step 3
spanning-tree loopguard default
Step 4
end
Step 5
show running-config
Step 6
copy running-config startup-config
To globally disable loop guard, use the no spanning-tree loopguard default global configuration
command. You can override the setting of the no spanning-tree loopguard default global configuration
command by using the spanning-tree guard loop interface configuration command.
Catalyst 3750 Switch Software Configuration Guide
19-18
Purpose
Enter global configuration mode.
Specify an interface to configure, and enter interface configuration mode.
Enable root guard on the interface.
By default, root guard is disabled on all interfaces.
Return to privileged EXEC mode.
Verify your entries.
Purpose
Verify which interfaces are alternate or root ports.
Enter global configuration mode.
Enable loop guard.
By default, loop guard is disabled.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 19
Configuring Optional Spanning-Tree Features
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