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Points to note
BPDU filter functionality can be set for each interface.
Command examples
1.
(config)# interface fastethernet 0/1
(config-if)# spanning-tree bpdufilter enable
(config-if)# exit
Sets BPDU filter functionality for port 0/1.
19.13.4 Configuring loop guards
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
Loop guards run on ports for which PortFast functionality is not set.
When the
loop guards are applied to all ports other than those with PortFast set. When loop
guard has been applied by default, use the
configuration command to disable loop guards.
Command examples
1.
(config)# spanning-tree loopguard default
Sets that loop guard functionality is to be applied for all ports other than those with
PortFast set.
2.
(config)# interface fastethernet 0/1
(config-if)# spanning-tree guard none
(config-if)# exit
Sets loop guards to be disabled on port 0/1 when loop guards are set to be applied
by default.
3.
(config)# no spanning-tree loopguard default
(config)# interface fastethernet 0/2
(config-if)# spanning-tree guard loop
(config-if)# exit
Deletes settings to apply loop guards by default, and applies loop guards by setting
for each port, for port 0/2.
19.13.5 Setting root guards
When a switch is accidentally connected to a network or a setting is changed, the root
bridge might change, causing an unintended topology. Root guards can be set to prevent
this kind of unintended topology change.
Points to note
Root guards are set for designated ports. They are applied to all locations connected
to switches other than those that are root bridge candidates.
During root guard operation, if PVST+ is running, only ports for corresponding
spanning-tree loopguard default
19 Spanning Tree Protocol
configuration command is used,
spanning-tree guard none
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