Enabling Loop Guard - Cisco Catalyst 3750 Software Configuration Manual

Chapter 16 Configuring Optional Spanning-Tree Features
Command
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.
78-15870-01
Purpose
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.
Catalyst 3750 Metro Switch Software Configuration Guide
Configuring Optional Spanning-Tree Features
16-15