Enabling Loop Guard - Cisco Catalyst 2950 Software Configuration Manual

Configuring Optional Spanning-Tree Features
Command
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 ports 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 or MSTP. The MSTP is available only if you
have the enhanced software image installed on your switch. By default, it is globally disabled.
Beginning in privileged EXEC mode, follow these steps to enable loop guard on the switch:
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 2950 Desktop Switch Software Configuration Guide
12-20
Purpose
Verify your entries.
Purpose
Determine which ports are alternate or root ports.
Enter global configuration mode.
Enable loop guard on the switch.
By default, loop guard is disabled.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 12 Configuring Optional Spanning-Tree Features
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