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220-1201 Practice Question: A technician is troubleshooting a network where…
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?
⚠ Common exam trap
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.
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.
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.
- ✗
The switch firmware is outdated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Outdated firmware might cause bugs or performance issues, but it would not directly cause CRC errors; those are physical layer issues.
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 |
Go deeper
Related to this question
Learn chapter
Mobile Device Connectivity
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
Key term
Ethernet
Ethernet is a wired networking technology that connects devices like computers, printers, and servers to each other and to the internet using cables.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1201 practice question is part of Courseiva's free CompTIA 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 220-1201 exam.