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Routing & Switching · Advanced

Loop Guard

An STP feature that stops a non-designated port from becoming designated when BPDUs stop arriving, preventing loops from unidirectional links.

Definition

If a root or alternate port stops receiving BPDUs, loop guard places it in loop-inconsistent state instead of transitioning to forwarding. It recovers when BPDUs resume. It complements UDLD.

Example

spanning-tree guard loop

Exam tip

Loop guard and root guard cannot be enabled on the same port.

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