Which mechanism should be added to a network design to identify unidirectional Spanning Tree Protocol failures through BPDU loss?

Question

Options

• ARoot guard
• BBPDU guard
• CLoop guard
• DUDLD

• A
  5% (2)
• B
  15% (6)
• C
  73% (29)
• D
  8% (3)

Explanation

Loop Guard protects against unidirectional link failures by monitoring non-designated (blocking) ports for incoming BPDUs - when BPDUs stop arriving (indicating a one-way failure), Loop Guard transitions the port to a loop-inconsistent state rather than allowing it to erroneously move to forwarding, which would create a bridging loop.

Why the distractors are wrong:

• A. Root guard - Prevents inferior switches from becoming the root by rejecting superior BPDUs received on protected ports; it reacts to receiving unexpected BPDUs, not to BPDU loss.
• B. BPDU guard - Shuts down PortFast-enabled edge ports when any BPDU is received; it's for protecting access ports from rogue switches, not for detecting unidirectional failures.
• D. UDLD - Also detects unidirectional links, but uses its own Layer 2 echo/probe messages rather than monitoring BPDU loss, so it operates independently of STP state.

Memory tip: Think "Loop Guard = loss guard." It guards against loops caused by BPDU loss on blocking ports - if the port stops hearing BPDUs and would normally go to forwarding, Loop Guard freezes it in a safe inconsistent state instead.

No community discussion yet for this question.