350-001 · Question #40
Which statement is true about loop guard?
The correct answer is A. Loop Guard only operates on interfaces that are considered point-to-point by the spanning tree. Spanning Tree Loop Guard is designed to protect against loops caused by unidirectional link failures, where a port stops receiving BPDUs but the physical link remains up. When BPDUs stop arriving on a non-designated port, normal STP would transition that port to forwarding…
Question
Which statement is true about loop guard?
Options
- ALoop Guard only operates on interfaces that are considered point-to-point by the spanning tree.
- BLoop Guard only operates on root ports.
- CLoop Guard only operates on designated ports
- DLoop Guard only operates on edge ports
How the community answered
(14 responses)- A93% (13)
- B7% (1)
Explanation
Spanning Tree Loop Guard is designed to protect against loops caused by unidirectional link failures, where a port stops receiving BPDUs but the physical link remains up. When BPDUs stop arriving on a non-designated port, normal STP would transition that port to forwarding (assuming the designated bridge failed), potentially creating a loop. Loop Guard instead moves the port into a loop-inconsistent blocking state. Critically, Loop Guard is only effective - and should only be configured - on point-to-point links (full-duplex links that STP classifies as point-to-point). It is not applicable to shared/half-duplex segments. It operates on root ports and alternate ports, not on designated ports.
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