- A
BPDU Guard has errdisabled the port because a BPDU was received on an access port.
Why wrong: BPDU Guard places a port in errdisable state, not root-inconsistent. Also, the port is an uplink trunk, typically not configured with portfast and BPDU Guard in this scenario.
- B
BPDU Filter is blocking inbound BPDUs, causing the switch to fail to detect the topology change and isolate the port.
Why wrong: BPDU Filter either ignores BPDUs (if enabled globally) or stops sending/receiving BPDUs (per-port). It does not cause a root-inconsistent state; it would silently filter superior BPDUs without blocking the port.
- C
Root Guard has placed the port into root-inconsistent state because the new switch advertised a superior BPDU.
Root Guard is designed to prevent the port from becoming a root port. Upon receiving a superior BPDU (lower bridge ID), it places the port in root-inconsistent state, effectively blocking traffic. This directly matches the symptom described.
- D
Loop Guard has detected a unidirectional link and placed the port in a blocking state to prevent a loop.
Why wrong: Loop Guard monitors for the absence of BPDUs on a non-designated port. If BPDUs stop arriving, it loops-inconsistent, not root-inconsistent. The scenario mentions receiving a superior BPDU, not missing BPDUs.
Quick Answer
The answer is Root Guard has placed the port into a root-inconsistent state because the new access switch advertised a superior BPDU. Root Guard is designed to protect the spanning-tree topology by monitoring any port where it is enabled; if a superior BPDU—one with a lower bridge priority than the current root bridge—arrives on that port, Root Guard immediately transitions the port to a root-inconsistent state, blocking all traffic to prevent the new switch from usurping the root bridge role. On the CCNA 200-301 v2 exam, this scenario tests your understanding of STP security mechanisms and how they differ from features like BPDU Guard or Loop Guard; a common trap is confusing root-inconsistent with errdisable, but root-inconsistent is a specific STP state triggered only by superior BPDUs on a Root Guard port. Remember the mnemonic: “Root Guard rejects a better root” — if a switch tries to become king, Root Guard locks the door.
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 engineer notices that an uplink port on a distribution switch has moved to a root-inconsistent state and is blocking traffic. The port is configured with Root Guard and is connected to a new access switch. The new access switch has a lower bridge priority than the current root bridge. What is the most likely cause?
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 has placed the port into root-inconsistent state because the new switch advertised a superior BPDU.
The port moved to root-inconsistent because Root Guard is enabled. Root Guard detects superior BPDUs (lower bridge ID) and immediately places the port in a broken state (root-inconsistent) to prevent the new switch from becoming the root bridge, thereby blocking traffic. This matches the symptom perfectly. Other features would manifest differently.
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.
- ✗
BPDU Guard has errdisabled the port because a BPDU was received on an access port.
Why it's wrong here
BPDU Guard places a port in errdisable state, not root-inconsistent. Also, the port is an uplink trunk, typically not configured with portfast and BPDU Guard in this scenario.
- ✗
BPDU Filter is blocking inbound BPDUs, causing the switch to fail to detect the topology change and isolate the port.
Why it's wrong here
BPDU Filter either ignores BPDUs (if enabled globally) or stops sending/receiving BPDUs (per-port). It does not cause a root-inconsistent state; it would silently filter superior BPDUs without blocking the port.
- ✓
Root Guard has placed the port into root-inconsistent state because the new switch advertised a superior BPDU.
Why this is correct
Root Guard is designed to prevent the port from becoming a root port. Upon receiving a superior BPDU (lower bridge ID), it places the port in root-inconsistent state, effectively blocking traffic. This directly matches the symptom described.
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.
- ✗
Loop Guard has detected a unidirectional link and placed the port in a blocking state to prevent a loop.
Why it's wrong here
Loop Guard monitors for the absence of BPDUs on a non-designated port. If BPDUs stop arriving, it loops-inconsistent, not root-inconsistent. The scenario mentions receiving a superior BPDU, not missing 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 Guard has placed the port into root-inconsistent state because the new switch advertised a superior BPDU.Correct answer▾
Why this is correct
Root Guard is designed to prevent the port from becoming a root port. Upon receiving a superior BPDU (lower bridge ID), it places the port in root-inconsistent state, effectively blocking traffic. This directly matches the symptom described.
✗BPDU Guard has errdisabled the port because a BPDU was received on an access port.Wrong answer — click to see why▾
Why this is wrong here
Candidates mistakenly equate BPDU Guard with any BPDU-induced blocking, but the state 'root-inconsistent' is specific to Root Guard.
✗BPDU Filter is blocking inbound BPDUs, causing the switch to fail to detect the topology change and isolate the port.Wrong answer — click to see why▾
Why this is wrong here
Candidates may think that filtering BPDUs leads to port isolation, but BPDU Filter would not trigger a protective state like root-inconsistent.
✗Loop Guard has detected a unidirectional link and placed the port in a blocking state to prevent a loop.Wrong answer — click to see why▾
Why this is wrong here
Candidates often confuse Loop Guard and Root Guard because both can cause inconsistent states, but Loop Guard triggers loop-inconsistent, not root-inconsistent, and is triggered by BPDU loss, not receipt of superior BPDUs.
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
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Scenario analysis trap
BPDU Guard places a port in errdisable state, not root-inconsistent. Also, the port is an uplink trunk, typically not configured with portfast and BPDU Guard in this scenario.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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Switching and Network Access — study guide chapter
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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 has placed the port into root-inconsistent state because the new switch advertised a superior BPDU. — The port moved to root-inconsistent because Root Guard is enabled. Root Guard detects superior BPDUs (lower bridge ID) and immediately places the port in a broken state (root-inconsistent) to prevent the new switch from becoming the root bridge, thereby blocking traffic. This matches the symptom perfectly. Other features would manifest differently.
What should I do if I get this 200-301 question wrong?
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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Last reviewed: Jun 14, 2026
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