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.”
220-1201 Network Configuration Concepts Practice Question
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.
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
This question tests understanding of network errors and their causes. CRC errors indicate data corruption during transmission, often due to physical layer issues like faulty cabling, electromagnetic interference, or damaged connectors. Since multiple ports are affected, a common cabling problem is likely.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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
Access ports place end devices into a single VLAN.
✗
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: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 220-1201 questions on switching, trunking, and access-port configuration.
Network Configuration Concepts — This question tests Network Configuration Concepts — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The Ethernet cables are run too close to power cables — This question tests understanding of network errors and their causes. CRC errors indicate data corruption during transmission, often due to physical layer issues like faulty cabling, electromagnetic interference, or damaged connectors. Since multiple ports are affected, a common cabling problem is likely.
What should I do if I get this 220-1201 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 220-1201 questions on switching, trunking, and access-port configuration.
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?
Access ports place end devices into a single VLAN.
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