- A
The switch is configured with the wrong VLAN assignments
Why wrong: VLAN misconfigurations would cause connectivity issues but not CRC errors; CRC errors are physical layer problems.
- B
The workstations have duplicate IP addresses
Why wrong: Duplicate IP addresses cause IP conflicts and connectivity drops, but they do not produce CRC errors on the switch.
- C
The Ethernet cables are run too close to power cables
Electromagnetic interference from power cables can corrupt data signals, leading to CRC errors on multiple ports.
- D
The switch firmware is outdated
Why wrong: Outdated firmware might cause bugs or performance issues, but it would not directly cause CRC errors; those are physical layer issues.
Question 16 of 1,020
Troubleshooting CRC Errors: Cables Too Close to Power Lines
This 220-1201 practice question tests your understanding of network configuration concepts. 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 technician is troubleshooting a network where users report intermittent connectivity. The technician finds that the switch logs show excessive CRC errors on multiple ports connected to different workstations. What is the most likely cause of these errors?
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.
Quick Answer
The answer is that Ethernet cables run too close to power lines are the most likely cause of CRC errors on multiple switch ports. CRC errors occur when data frames arrive corrupted, typically from electromagnetic interference (EMI) disrupting the signal during transmission. Because the issue affects multiple ports connected to different workstations, a common environmental factor like cabling routed alongside electrical lines is the culprit, rather than a single faulty NIC or connector. On the CompTIA A+ Core 1 220-1201 exam, this question tests your ability to distinguish physical-layer problems from software or configuration issues—a common trap is to blame a bad patch cable or a failing switch, but the key clue is the widespread nature of the errors. Remember that CRC errors point to signal integrity, so think of interference sources first. A helpful memory tip: “CRC means check the route—keep data cables away from power to avoid the shower.”
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 Ethernet cables are run too close to power cables
CRC errors indicate data corruption at the physical layer, typically caused by electromagnetic interference (EMI) from nearby power cables. Running Ethernet cables too close to power cables induces noise, corrupting frames and causing CRC mismatches at the switch port.
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 switch is configured with the wrong VLAN assignments
Why it's wrong here
VLAN misconfigurations would cause connectivity issues but not CRC errors; CRC errors are physical layer problems.
- ✗
The workstations have duplicate IP addresses
Why it's wrong here
Duplicate IP addresses cause IP conflicts and connectivity drops, but they do not produce CRC errors on the switch.
- ✓
The Ethernet cables are run too close to power cables
Why this is correct
Electromagnetic interference from power cables can corrupt data signals, leading to CRC errors on multiple ports.
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 firmware is outdated
Why it's wrong here
Outdated firmware might cause bugs or performance issues, but it would not directly cause CRC errors; those are physical layer issues.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA A+ exams often test the distinction between physical-layer issues (CRC errors, runts, giants) and logical-layer issues (VLAN misconfigurations, IP conflicts), so candidates mistakenly attribute CRC errors to software or configuration problems instead of cabling interference.
Detailed technical explanation
How to think about this question
CRC (Cyclic Redundancy Check) is a 4-byte frame trailer computed by the sender and verified by the receiver; if the computed CRC does not match, the frame is discarded. EMI from power cables can alter the signal on unshielded twisted-pair (UTP) cabling, especially if the cables are run in parallel for long distances without proper separation (e.g., less than 12 inches for 1000BASE-T).
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
What to study next
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FAQ
Questions learners often ask
What does this 220-1201 question test?
Network Configuration Concepts — This question tests Network Configuration Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Ethernet cables are run too close to power cables — CRC errors indicate data corruption at the physical layer, typically caused by electromagnetic interference (EMI) from nearby power cables. Running Ethernet cables too close to power cables induces noise, corrupting frames and causing CRC mismatches at the switch port.
What should I do if I get this 220-1201 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: Jul 4, 2026
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