- A
Loop Guard
Why wrong: Loop Guard protects against unidirectional links and places a port into a loop-inconsistent state, not root-inconsistent.
- B
Root Guard
Root Guard ensures that a port cannot become a root port. When a superior BPDU is received on a Root Guard-enabled port, the port transitions to a root-inconsistent state and blocks traffic, exactly as described in the scenario.
- C
BPDU Guard
Why wrong: BPDU Guard immediately error-disables a port that receives a BPDU, placing it in an err-disabled state rather than a root-inconsistent state.
- D
BPDU Filter
Why wrong: BPDU Filter suppresses all BPDU transmission and reception on the port. It does not place the port in any protective spanning-tree state; instead, it can create bridging loops by ignoring BPDUs.
Quick Answer
The answer is Root Guard, as it directly causes the root-inconsistent state when a superior BPDU is received on a port configured with this feature. Root Guard forces a port to remain a designated port, so if a switch connected to that port advertises a lower bridge ID—claiming to be a better root bridge—the port immediately enters a root-inconsistent state and blocks all traffic to prevent the unauthorized switch from becoming the root. On the CCNA 200-301 v2 exam, this scenario tests your understanding of spanning-tree protection mechanisms and their distinct symptoms; a common trap is confusing Root Guard with BPDU Guard, but remember that BPDU Guard err-disables the port upon receiving any BPDU, while Root Guard only blocks when a superior BPDU is received. A helpful memory tip: think of Root Guard as a "bouncer" that blocks any switch trying to steal the root role—if a superior BPDU shows up, the port gets put in time-out (root-inconsistent).
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network administrator implements a set of spanning-tree enhancements to secure the switching infrastructure. Later, a help desk ticket reports that a user in a remote office cannot connect to any network resources. While investigating, the administrator notices that the switch port connecting the remote office switch to the distribution switch is in a 'root-inconsistent' state and is blocking traffic. Which protection feature, if misapplied, most likely caused this issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Root Guard
Root Guard is the correct answer because it forces an interface to be a designated port. If a switch receives a superior BPDU (indicating a root bridge with a lower bridge ID) on a Root Guard-enabled port, the port is placed into a 'root-inconsistent' state and blocks traffic to prevent the attached switch from becoming the root bridge. This matches the symptom described: a port in 'root-inconsistent' state blocking traffic after spanning-tree enhancements were applied.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Loop Guard
Why it's wrong here
Loop Guard protects against unidirectional links and places a port into a loop-inconsistent state, not root-inconsistent.
- ✓
Root Guard
Why this is correct
Root Guard ensures that a port cannot become a root port. When a superior BPDU is received on a Root Guard-enabled port, the port transitions to a root-inconsistent state and blocks traffic, exactly as described in the scenario.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
BPDU Guard
Why it's wrong here
BPDU Guard immediately error-disables a port that receives a BPDU, placing it in an err-disabled state rather than a root-inconsistent state.
- ✗
BPDU Filter
Why it's wrong here
BPDU Filter suppresses all BPDU transmission and reception on the port. It does not place the port in any protective spanning-tree state; instead, it can create bridging loops by ignoring BPDUs.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Root GuardCorrect answer▾
Why this is correct
Root Guard ensures that a port cannot become a root port. When a superior BPDU is received on a Root Guard-enabled port, the port transitions to a root-inconsistent state and blocks traffic, exactly as described in the scenario.
✗Loop GuardWrong answer — click to see why▾
Why this is wrong here
A loop-inconsistent state is different from the root-inconsistent state observed. Loop Guard acts when BPDUs stop arriving, not when they appear with a superior root claim.
✗BPDU GuardWrong answer — click to see why▾
Why this is wrong here
While BPDU Guard also reacts to incoming BPDUs, it puts the port in err-disabled (shutdown) state, not a blocking state named 'root-inconsistent'. The symptom described is not error-disabled.
✗BPDU FilterWrong answer — click to see why▾
Why this is wrong here
BPDU Filter would not cause the port to show a root-inconsistent state. The symptom is a protective blocking state, which BPDU Filter does not provide.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between 'root-inconsistent' (Root Guard) and 'loop-inconsistent' (Loop Guard) states, and the trap here is that candidates confuse the two or assume BPDU Guard is responsible for any BPDU-related blocking.
Detailed technical explanation
How to think about this question
Root Guard works by comparing the received BPDU's root bridge ID against the local bridge ID; if the received BPDU advertises a superior root (lower bridge ID), the port is immediately moved to the 'root-inconsistent' (blocking) state. This feature is typically applied on ports that should never become root ports, such as access ports or ports connecting to end-user switches. In a real-world scenario, a misapplied Root Guard on a distribution-to-access link could block legitimate root bridge advertisements from a properly configured root switch, causing connectivity loss for downstream users.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Switching and Network Access — This question tests Switching and Network Access — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Root Guard — Root Guard is the correct answer because it forces an interface to be a designated port. If a switch receives a superior BPDU (indicating a root bridge with a lower bridge ID) on a Root Guard-enabled port, the port is placed into a 'root-inconsistent' state and blocks traffic to prevent the attached switch from becoming the root bridge. This matches the symptom described: a port in 'root-inconsistent' state blocking traffic after spanning-tree enhancements were applied.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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