DELL 9.7(0.0) User Manual

–

–

–

• You cannot enable root guard and loop guard at the same time on an STP port. For example, if you 

configure loop guard on a port on which root guard is already configured, the following error 

message is displayed: % Error: RootGuard is configured. Cannot configure LoopGuard.

• Enabling Portfast BPDU guard and loop guard at the same time on a port results in a port that remains 

in a blocking state and prevents traffic from flowing through it. For example, when Portfast BPDU 

guard and loop guard are both configured:

– If a BPDU is received from a remote device, BPDU guard places the port in an Err-Disabled 

Blocking state and no traffic is forwarded on the port.

– If no BPDU is received from a remote device, loop guard places the port in a Loop-Inconsistent 

Blocking state and no traffic is forwarded on the port.

• When used in a PVST+ network, STP loop guard is performed per-port or per-port channel at a VLAN 

level. If no BPDUs are received on a VLAN interface, the port or port-channel transitions to a Loop-

Inconsistent (Blocking) state only for this VLAN.

To enable a loop guard on an STP-enabled port or port-channel interface, use the following command.

• Enable loop guard on a port or port-channel interface.

INTERFACE mode or INTERFACE PORT-CHANNEL mode

spanning-tree {0 | mstp | rstp | pvst} loopguard

– 0: enables loop guard on an STP-enabled port assigned to instance 0.
– mstp: enables loop guard on an MSTP-enabled port.
– rstp: enables loop guard on an RSTP-enabled port.
– pvst: enables loop guard on a PVST-enabled port.

To disable STP loop guard on a port or port-channel interface, use the no spanning-tree 0 
loopguard command in an INTERFACE configuration mode.
To verify the STP loop guard configuration on a port or port-channel interface, use the show spanning-
tree 0 guard [interface interface] command in a global configuration mode.

Displaying STP Guard Configuration

To display the STP guard configuration, use the following command.

The following example shows an STP network (instance 0) in which:

• Root guard is enabled on a port that is in a root-inconsistent state.
• Loop guard is enabled on a port that is in a listening state.
• BPDU guard is enabled on a port that is shut down (Error Disabled state) after receiving a BPDU.

• Verify the STP guard configured on port or port-channel interfaces.

show spanning-tree 0 guard [interface interface]

Example of Viewing STP Guard Configuration

Dell#show spanning-tree 0 guard

Interface

Name    Instance Sts          Guard type

--------- -------- --------- ----------

Te 0/1  0        INCON(Root)  Rootguard

Spanning Tree Protocol (STP)

883