Cisco Catalyst 3750 - Enabling Loop Guard

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Catalyst 3750 Metro Switch Software Configuration Guide
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Chapter 16 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
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.
Note You cannot enable both loop guard and root guard at the same time.
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.
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.
Step 4
end Return to privileged EXEC mode.
Step 5
show running-config Verify your entries.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Command Purpose
Step 1
show spanning-tree active
or
show spanning-tree mst
Verify which interfaces are alternate or root ports.
Step 2
configure terminal Enter global configuration mode.
Step 3
spanning-tree loopguard default Enable loop guard.
By default, loop guard is disabled.
Step 4
end Return to privileged EXEC mode.
Step 5
show running-config Verify your entries.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.