- A
Runts are typically caused by CRC errors on the transmitting device.
Why wrong: Runts are undersized frames. CRC errors indicate corrupted bits in a received frame, not a cause of frame shortening.
- B
Late collisions on a half-duplex interface can indicate a duplex mismatch with the connected device.
Late collisions occur after the frame's first 512 bits have been transmitted, typically due to one side operating in full-duplex while the other is half-duplex.
- C
The 'show interfaces' command displays the number of CRC errors and runts on an interface.
The output of show interfaces includes a line for runts, giants, CRC errors, and other input-error counters.
- D
Full-duplex interfaces use CSMA/CD to detect collisions before transmitting.
Why wrong: Full-duplex Ethernet simultaneously transmits and receives without contention, bypassing CSMA/CD.
- E
Auto-MDIX can resolve a duplex mismatch by renegotiating the speed and duplex settings.
Why wrong: Auto-MDIX is a physical-layer feature that detects and corrects for crossover cable requirements.
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 statements correctly describe interface errors and duplex mismatches on Cisco switches?
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
Late collisions on a half-duplex interface can indicate a duplex mismatch with the connected device.
Option B is correct because late collisions occur when a frame is transmitted onto the wire and collides after the first 512 bit-times of the frame. In a half-duplex Ethernet segment, a duplex mismatch causes the full-duplex side to never defer and transmit at any time, while the half-duplex side expects to detect collisions only during the collision window. When the full-duplex device sends a frame while the half-duplex device is already transmitting, the half-duplex device detects a collision after the 512-bit window, resulting in a late collision.
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.
- ✗
Runts are typically caused by CRC errors on the transmitting device.
Why it's wrong here
Runts are undersized frames. CRC errors indicate corrupted bits in a received frame, not a cause of frame shortening.
- ✓
Late collisions on a half-duplex interface can indicate a duplex mismatch with the connected device.
Why this is correct
Late collisions occur after the frame's first 512 bits have been transmitted, typically due to one side operating in full-duplex while the other is half-duplex.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
The 'show interfaces' command displays the number of CRC errors and runts on an interface.
Why this is correct
The output of show interfaces includes a line for runts, giants, CRC errors, and other input-error counters.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Full-duplex interfaces use CSMA/CD to detect collisions before transmitting.
Why it's wrong here
Full-duplex Ethernet simultaneously transmits and receives without contention, bypassing CSMA/CD.
- ✗
Auto-MDIX can resolve a duplex mismatch by renegotiating the speed and duplex settings.
Why it's wrong here
Auto-MDIX is a physical-layer feature that detects and corrects for crossover cable requirements.
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.
✓Late collisions on a half-duplex interface can indicate a duplex mismatch with the connected device.Correct answer▾
Why this is correct
Late collisions occur after the frame's first 512 bits have been transmitted, typically due to one side operating in full-duplex while the other is half-duplex.
✗Runts are typically caused by CRC errors on the transmitting device.Wrong answer — click to see why▾
Why this is wrong here
Runts result from collisions on half-duplex links or faulty network interface cards, not from CRC errors.
✗Full-duplex interfaces use CSMA/CD to detect collisions before transmitting.Wrong answer — click to see why▾
Why this is wrong here
CSMA/CD is only used in half-duplex environments; full-duplex disables collision detection entirely.
✗Auto-MDIX can resolve a duplex mismatch by renegotiating the speed and duplex settings.Wrong answer — click to see why▾
Why this is wrong here
Auto-MDIX does not participate in speed or duplex negotiation; that function is handled by auto-negotiation (IEEE 802.3u).
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 late collisions (which occur after the 64-byte window and indicate a duplex mismatch) and early collisions (which occur within the window and are normal in half-duplex), and candidates mistakenly think that all collisions are normal or that CRC errors are the primary cause of runts.
Detailed technical explanation
How to think about this question
Late collisions are a key symptom of duplex mismatch because the full-duplex side ignores the interframe gap and transmits immediately, while the half-duplex side must defer to the carrier sense. The collision detection window for 10/100 Mbps Ethernet is 512 bit-times (64 bytes); if a collision occurs after that, the half-duplex interface does not retransmit the frame, leading to data loss and high error rates. In a real-world scenario, a switch port set to full-duplex connected to a host set to half-duplex will show increasing late collisions on the switch's half-duplex interface, often accompanied by CRC errors and runts.
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 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
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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: Late collisions on a half-duplex interface can indicate a duplex mismatch with the connected device. — Option B is correct because late collisions occur when a frame is transmitted onto the wire and collides after the first 512 bit-times of the frame. In a half-duplex Ethernet segment, a duplex mismatch causes the full-duplex side to never defer and transmit at any time, while the half-duplex side expects to detect collisions only during the collision window. When the full-duplex device sends a frame while the half-duplex device is already transmitting, the half-duplex device detects a collision after the 512-bit window, resulting in a late collision.
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.
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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