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Dell Configuration Guide for the S4048–ON System 9.14.2.6

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Configuring Loop Guard

Enable STP loop guard on a per-port or per-port channel basis.

The following conditions apply to a port enabled with loop guard:
  • Loop guard is supported on any STP-enabled port or port-channel interface.
  • Loop guard is supported on a port or port-channel in any spanning tree mode:
  • 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.


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