The correct answer is a faulty cable, as CRC errors on a switch interface directly indicate that incoming frames have failed the cyclic redundancy check, meaning data corruption occurred during transmission. A faulty cable is the most likely cause because physical defects like breaks, kinks, or poor shielding introduce electrical interference and signal degradation, altering the bits within the frame. On the CompTIA ITF+ FC0-U61 exam, this question tests your understanding of Layer 1 troubleshooting, where CRC errors are a classic symptom of cabling issues rather than configuration problems. A common trap is to blame duplex mismatch, but while that can cause errors, a faulty cable is the primary suspect when CRC errors are present. Remember the memory tip: “CRC equals cable—check the physical link first.”
FC0-U61 Infrastructure Practice Question
This FC0-U61 practice question tests your understanding of infrastructure. 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.
A technician notices that a switch interface is showing many CRC errors. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Faulty cable
CRC errors indicate that frames received on the interface have failed the cyclic redundancy check, meaning the data has been corrupted during transmission. A faulty cable is the most common cause of such corruption because it can introduce electrical interference, signal degradation, or physical breaks that alter the bits in the frame. While duplex mismatch can cause CRC errors in some cases, a faulty cable is the primary suspect when CRC errors are present.
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.
✗
Duplex mismatch
Why it's wrong here
Duplex mismatch usually causes collisions and late collisions, not CRC errors.
✓
Faulty cable
Why this is correct
CRC errors are often due to damaged cables, poor connections, or electromagnetic interference.
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.
✗
Incorrect IP configuration
Why it's wrong here
IP configuration errors do not cause CRC errors at the physical layer.
✗
MAC address flooding
Why it's wrong here
MAC flooding is a security exploit that fills the switch's MAC table, not a cause of CRC errors.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often associate CRC errors with duplex mismatch because both can appear under high-traffic conditions, but Cisco specifically tests that CRC errors point to physical-layer issues like cabling, while duplex mismatch manifests as late collisions and runts.
Detailed technical explanation
How to think about this question
CRC errors occur when the frame's trailer checksum computed by the receiver does not match the sender's checksum, often due to noise, attenuation, or impedance mismatches in the cable. In Ethernet, the CRC is a 32-bit field calculated over the entire frame (excluding the preamble and SFD), and even a single bit flip will cause a mismatch. Real-world scenarios include using a cable that exceeds the maximum length (100 meters for Cat5e/6), using a damaged patch cable, or running a cable near high-voltage power lines that induce electromagnetic interference.
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 FC0-U61 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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Infrastructure — This question tests Infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Faulty cable — CRC errors indicate that frames received on the interface have failed the cyclic redundancy check, meaning the data has been corrupted during transmission. A faulty cable is the most common cause of such corruption because it can introduce electrical interference, signal degradation, or physical breaks that alter the bits in the frame. While duplex mismatch can cause CRC errors in some cases, a faulty cable is the primary suspect when CRC errors are present.
What should I do if I get this FC0-U61 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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Question Discussion
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