Cisco
352-001 · Question #177
352-001 Question #177: Real Exam Question with Answer & Explanation
The correct answer is C: root guard. Root guard prevents a port from accepting a superior BPDU that would trigger an unintended root bridge election, enforcing the designed STP topology and keeping traffic on optimal paths.
Question
Which mechanism prevents switched traffic from traversing suboptimal paths on the network?
Options
- APortFast
- BUDLD
- Croot guard
- DBridge Assurance
- EBPDU Filter
Explanation
Root guard prevents a port from accepting a superior BPDU that would trigger an unintended root bridge election, enforcing the designed STP topology and keeping traffic on optimal paths.
Common mistakes.
- A. PortFast accelerates port transitions to forwarding state for access ports by bypassing listening and learning, but has no effect on root bridge election or path selection.
- B. UDLD detects unidirectional link conditions by verifying bidirectional traffic flow, which addresses physical link failures rather than STP path optimality.
- D. Bridge Assurance protects against unidirectional failures by requiring periodic BPDUs on all network ports, but it does not prevent a superior BPDU from triggering a suboptimal root bridge election.
- E. BPDU Filter disables STP BPDU processing on a port entirely, which can create bridging loops and does nothing to enforce root bridge placement or prevent suboptimal paths.
Concept tested. Spanning Tree root guard enforcing optimal root bridge placement
Reference. https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10588-74.html
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