26.10.4 Configuring Loop Guard
When a unidirectional link fault occurs, such as when a one-way line is cut, and BPDU reception is cut off, a loop might have occurred. Loop guard functionality prevents these kinds of loops from occurring.
- Points to note
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Loop guards run on ports for which PortFast functionality is not set.
When the spanning-tree loopguard default command is set, loop guards are applied to all ports other than those with PortFast set. When this is applied by default, the spanning-tree guard none command is set to disable loop guards.
Command examples
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(config)# spanning-tree loopguard default
Sets that loop guard functionality is to be applied for all ports other than those with PortFast set.
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(config)# interface gigabitethernet 1/0/1
(config-if)# spanning-tree guard none
(config-if)# exit
Sets loop guards to be disabled on port 1/0/1 when loop guards are set to be applied by default.
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(config)# no spanning-tree loopguard default
(config)# interface gigabitethernet 1/0/2
(config-if)# spanning-tree guard loop
Deletes settings to apply loop guards by default, and applies loop guards by setting for each port, for port 1/0/2. Also, loop guard is applied with per-port settings for ports 1, 0, and 2.