hardMultiple Choice
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
Wrong VLAN assignments cause connectivity failures because frames land in the wrong broadcast domain, but they do not corrupt frame checksums. VLAN misconfiguration is the right answer when hosts cannot reach gateways or each other despite clean link statistics, not when CRC counters climb.
- ✗
The workstations have duplicate IP addresses
Why it's wrong here
Duplicate IP addresses trigger ARP conflicts and intermittent loss of connectivity, but they do not corrupt frames, so CRC errors would not appear. Duplicate addressing is the correct diagnosis when logs show IP conflict warnings or ARP replies from two MAC addresses, not frame check failures.
- ✓
The Ethernet cables are run too close to power cables
Why this is correct
Electromagnetic interference from nearby power cables corrupts signals on the copper runs, producing CRC mismatches at the switch. Because the errors appear across multiple ports feeding different workstations, a shared environmental factor such as parallel mains cabling is the likely culprit, satisfying the intermittent-connectivity symptom described in the stem.
- ✗
The switch firmware is outdated
Why it's wrong here
Outdated firmware can cause driver-level faults, but CRC errors on multiple ports across different workstations point to a shared physical-layer fault such as cabling, duplex mismatch or interference. Firmware updates would be the right step when a known bug affects a specific NIC or switch model.
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 |
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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.