- A
The cable connecting the server to the switch is faulty.
Why wrong: A faulty cable can cause CRC errors, but typically also causes input errors, and may still experience collisions if both sides are half-duplex. It does not specifically explain the presence of runts alongside CRC errors without collisions.
- B
The switch port is configured for full-duplex, but the server's NIC is set to half-duplex.
A duplex mismatch where the switch uses full-duplex and the server uses half-duplex results in the full-duplex side (switch) showing runts and CRC errors without collisions, while the half-duplex side sees collisions. This matches the 'show interfaces' output and explains the slow transfers due to excessive retransmissions.
- C
The switch port speed is set to 100 Mbps, but the server NIC is set to 10 Mbps.
Why wrong: A hard-set speed mismatch (100 vs 10) usually results in the link not coming up because both sides cannot establish a valid connection. The interfaces would be in a down/down state, not forwarding traffic, so file transfers would be impossible, not just slow.
- D
The server's NIC driver is outdated, causing packet loss.
Why wrong: An outdated driver could lead to performance issues or packet loss, but it would not selectively generate runts and CRC errors on the switch port. Those errors indicate Layer 1 or Layer 2 issues on the link, typically related to physical layer problems or duplex mismatches.
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. 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 notices that file transfers to a server are extremely slow, and on the switch interface connecting to the server, the output of 'show interfaces' indicates a high number of runts and CRC errors, but no collisions. Which of the following 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
The switch port is configured for full-duplex, but the server's NIC is set to half-duplex.
The combination of runts (frames smaller than 64 bytes) and CRC errors with zero collisions is a classic symptom of a duplex mismatch. When one side operates at full-duplex and the other at half-duplex, the half-duplex side will detect collisions and invoke its backoff algorithm, causing the full-duplex side to receive truncated frames (runts) and frames with invalid FCS (CRC errors). The switch interface statistics show no collisions because the switch port is full-duplex and does not detect collisions, while the server's half-duplex NIC is causing the corruption.
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.
- ✗
The cable connecting the server to the switch is faulty.
Why it's wrong here
A faulty cable can cause CRC errors, but typically also causes input errors, and may still experience collisions if both sides are half-duplex. It does not specifically explain the presence of runts alongside CRC errors without collisions.
- ✓
The switch port is configured for full-duplex, but the server's NIC is set to half-duplex.
Why this is correct
A duplex mismatch where the switch uses full-duplex and the server uses half-duplex results in the full-duplex side (switch) showing runts and CRC errors without collisions, while the half-duplex side sees collisions. This matches the 'show interfaces' output and explains the slow transfers due to excessive retransmissions.
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.
- ✗
The switch port speed is set to 100 Mbps, but the server NIC is set to 10 Mbps.
Why it's wrong here
A hard-set speed mismatch (100 vs 10) usually results in the link not coming up because both sides cannot establish a valid connection. The interfaces would be in a down/down state, not forwarding traffic, so file transfers would be impossible, not just slow.
- ✗
The server's NIC driver is outdated, causing packet loss.
Why it's wrong here
An outdated driver could lead to performance issues or packet loss, but it would not selectively generate runts and CRC errors on the switch port. Those errors indicate Layer 1 or Layer 2 issues on the link, typically related to physical layer problems or duplex mismatches.
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.
✓The switch port is configured for full-duplex, but the server's NIC is set to half-duplex.Correct answer▾
Why this is correct
A duplex mismatch where the switch uses full-duplex and the server uses half-duplex results in the full-duplex side (switch) showing runts and CRC errors without collisions, while the half-duplex side sees collisions. This matches the 'show interfaces' output and explains the slow transfers due to excessive retransmissions.
✗The cable connecting the server to the switch is faulty.Wrong answer — click to see why▾
Why this is wrong here
While a faulty cable could cause CRC errors, it would likely produce other error types and might not exhibit the specific pattern of only runts and CRC errors with no collisions. This pattern strongly points to a duplex mismatch.
✗The switch port speed is set to 100 Mbps, but the server NIC is set to 10 Mbps.Wrong answer — click to see why▾
Why this is wrong here
A speed mismatch would generally cause the link to fail entirely; you wouldn't see interface errors because there would be no connectivity. The scenario describes connectivity with errors, so this is unlikely.
✗The server's NIC driver is outdated, causing packet loss.Wrong answer — click to see why▾
Why this is wrong here
Outdated drivers may cause performance problems, but they do not produce the specific interface error counters on the switch. The recorded runts and CRC errors point to a physical or data-link layer issue, not a driver problem.
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 symptoms of duplex mismatch versus cable faults, where candidates mistakenly attribute runts and CRC errors to a bad cable, ignoring the critical clue of zero collisions that points to a mismatch.
Detailed technical explanation
How to think about this question
In a duplex mismatch, the half-duplex side waits for the interframe gap before transmitting, but the full-duplex side transmits continuously, causing the half-duplex side to detect a collision and send a jam signal, which corrupts the frame. The full-duplex side never sees the collision but receives the corrupted frame as a runt (if truncated) or with a bad CRC. Cisco switches track these errors separately in 'show interfaces' output, and the absence of collisions on the full-duplex port is the key diagnostic clue.
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?
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The switch port is configured for full-duplex, but the server's NIC is set to half-duplex. — The combination of runts (frames smaller than 64 bytes) and CRC errors with zero collisions is a classic symptom of a duplex mismatch. When one side operates at full-duplex and the other at half-duplex, the half-duplex side will detect collisions and invoke its backoff algorithm, causing the full-duplex side to receive truncated frames (runts) and frames with invalid FCS (CRC errors). The switch interface statistics show no collisions because the switch port is full-duplex and does not detect collisions, while the server's half-duplex NIC is causing the corruption.
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
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.
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