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Question 223 of 1,052
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CCNA Practice Question: Which TWO symptoms are most likely to appear in…
This 200-301 practice question tests your understanding of 200-301 exam topics. 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.
Which TWO symptoms are most likely to appear in the output of 'show interfaces' when a duplex mismatch exists between a switch port and a connected host?
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
✓
Excessive collisions and CRC errors on the interface
A duplex mismatch occurs when one side operates at full duplex and the other at half duplex. The half-duplex side waits for a clear channel before sending, while the full-duplex side sends whenever it wants, causing collisions on the half-duplex link. This leads to excessive collisions and CRC errors on the half-duplex side. The full-duplex side does not detect collisions, so it sees runts and frame errors instead. Incorrect options: The 'show interfaces' output does not show 'auto-negotiation failed' as a direct symptom; it shows the negotiated duplex and speed. 'High input rate' is not a typical symptom of duplex mismatch; mismatches usually cause high error rates, not necessarily high throughput. 'Line protocol is down' indicates a more severe issue, such as a cable break or misconfiguration, not a duplex mismatch. 'Speed mismatch' is a separate issue that would cause the interface to go down or not come up at all.
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.
- ✓
Excessive collisions and CRC errors on the interface
Why this is correct
On the half-duplex side, collisions are normal but become excessive due to the full-duplex side transmitting without listening. CRC errors occur when frames are corrupted by collisions.
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.
- ✓
Runts and frame errors on the interface
Why this is correct
On the full-duplex side, collisions are not detected, so the interface sees fragments of frames (runts) and alignment errors due to frames truncated by collisions on the half-duplex side.
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.
- ✗
Auto-negotiation failed message in the interface output
Why it's wrong here
The 'show interfaces' output does not display 'auto-negotiation failed' as a direct symptom. It shows the negotiated duplex and speed, but a mismatch can occur even if auto-negotiation succeeds (e.g., when one side is manually configured).
- ✗
High input rate on the interface
Why it's wrong here
Duplex mismatch typically causes high error rates, not high throughput. The actual data rate may be low due to retransmissions, and the input rate shown is usually not elevated.
- ✗
Line protocol is down
Why it's wrong here
A duplex mismatch does not bring the line protocol down. The interface status remains up/up (or up/down if there is a physical issue), but errors accumulate. Line protocol down indicates a more fundamental problem like no keepalives or a Layer 2 issue.
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.
✓Excessive collisions and CRC errors on the interfaceCorrect answer▾
Why this is correct
On the half-duplex side, collisions are normal but become excessive due to the full-duplex side transmitting without listening. CRC errors occur when frames are corrupted by collisions.
✗Auto-negotiation failed message in the interface outputWrong answer — click to see why▾
Why this is wrong here
Auto-negotiation failure is not a symptom shown in 'show interfaces'; it is a cause that can lead to a mismatch, but the output itself does not report a failure message.
✗High input rate on the interfaceWrong answer — click to see why▾
Why this is wrong here
High input rate is not a characteristic symptom of duplex mismatch; it would more likely indicate a traffic burst or congestion.
✗Line protocol is downWrong answer — click to see why▾
Why this is wrong here
Duplex mismatch keeps the line protocol up; the interface continues to send and receive, albeit with errors.
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
Command / output trap
The 'show interfaces' output does not display 'auto-negotiation failed' as a direct symptom. It shows the negotiated duplex and speed, but a mismatch can occur even if auto-negotiation succeeds (e.g., when one side is manually configured).
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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FAQ
Questions learners often ask
What does this 200-301 question test?
Read the scenario before looking for a memorised answer.
What is the correct answer to this question?
The correct answer is: Excessive collisions and CRC errors on the interface — A duplex mismatch occurs when one side operates at full duplex and the other at half duplex. The half-duplex side waits for a clear channel before sending, while the full-duplex side sends whenever it wants, causing collisions on the half-duplex link. This leads to excessive collisions and CRC errors on the half-duplex side. The full-duplex side does not detect collisions, so it sees runts and frame errors instead. Incorrect options: The 'show interfaces' output does not show 'auto-negotiation failed' as a direct symptom; it shows the negotiated duplex and speed. 'High input rate' is not a typical symptom of duplex mismatch; mismatches usually cause high error rates, not necessarily high throughput. 'Line protocol is down' indicates a more severe issue, such as a cable break or misconfiguration, not a duplex mismatch. 'Speed mismatch' is a separate issue that would cause the interface to go down or not come up at all.
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.
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