OS10 Enterprise Edition User Guide Release 10.4.0E(R3)

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Loop guard

This information explains how to configure loop guard on an interface.

  • Enable loop guard on a per-port or port-channel interface in INTERFACE mode.
    spanning-tree guard {loop | root | none}
    • loop — Enables loop guard on an interface.
    • root — Enables root on an interface.
    • none — Enables the guard mode to none.
  • Disable loop guard on a port or port-channel interface in INTERFACE mode.
    no spanning-tree guard loop

Port enabled with loop guard conditions

  • Loop guard is supported on any STP-enabled port or port-channel interface in RPVST+ mode.
  • You cannot enable root guard and loop guard at the same time on an STP port — the loop guard configuration overwrites an existing root guard configuration and vice versa.
  • Enabling 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 you configure both Portfast BPDU guard and loop guard:
    • If a BPDU is received from a remote device, BPDU guard places the port in an Err-Disabled Blocking state and no traffic forwards on the port.
    • If no BPDU is received from a remote device which was sending BPDUs, loop guard places the port in a Loop-Inconsistent Blocking state and no traffic forwards on the port.
  • When used in a PVST+ network, STP loop guard performs per-port or per port-channel at a VLAN level. If no BPDUs are received on a port-channel interface, the port or port-channel transitions to a Loop-Inconsistent (Blocking) state only for this VLAN.

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