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352-001 · Question #374
352-001 Question #374: Real Exam Question with Answer & Explanation
The correct answer is B: It prevents switch loops by detecting one-way communications on the physical port.. UDLD detects unidirectional link conditions - where traffic flows in only one direction - and disables the affected port to prevent forwarding loops that STP would not catch.
Question
Which option describes an advantage of UDLD?
Options
- AIt makes the port go immediately into the forwarding state after being connected.
- BIt prevents switch loops by detecting one-way communications on the physical port.
- CIt prevents switched traffic from traversing suboptimal paths on the network.
- DIt prevents switch loops caused by uni-directional point-to-point link condition on Rapid PVST+
- EIt does not generate a spanning-tree topology change upon connecting and disconnecting a
- FIt allows small, unmanaged switches to be plugged into ports of access switches without the risk
Explanation
UDLD detects unidirectional link conditions - where traffic flows in only one direction - and disables the affected port to prevent forwarding loops that STP would not catch.
Common mistakes.
- A. Bypassing the listening and learning states to immediately enter forwarding is the function of PortFast, not UDLD.
- C. Preventing traffic from taking suboptimal paths is the function of Spanning Tree Protocol and its variants, not UDLD.
- D. UDLD is not specific to Rapid PVST+ and does not itself prevent loops caused by STP configuration - it addresses physical unidirectional link failures that STP cannot detect.
- E. Suppressing topology change notifications on link events is the behavior of PortFast, not UDLD.
- F. Preventing unauthorized switch attachment to access ports is the function of BPDU Guard, not UDLD.
Concept tested. UDLD detection of unidirectional physical link failures
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