220-1101 Hardware and Network Troubleshooting Practice Question
A technician is troubleshooting a network issue in an office. Users connected to a specific wall jack report intermittent connectivity. The switch port corresponding to that jack shows a high number of CRC errors. The technician removes the wall plate and finds that the twisted pairs are untwisted too far back from the RJ45 connector. Which of the following is the MOST likely cause of the CRC errors?
⚠ Common exam trap
Test-takers frequently confuse CRC errors with duplex mismatch or EMI, but the question explicitly ties the symptom to the physical termination defect, which is a direct cause of CRC errors per the CompTIA troubleshooting methodology.
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 twisted pairs are not properly terminated
CRC errors indicate that frames are being received with invalid checksums, typically due to signal integrity issues. Untwisting the pairs too far from the RJ45 connector disrupts the cable's impedance and crosstalk rejection, causing bit corruption that leads to CRC errors. Proper termination requires maintaining the twist up to within 0.5 inches (13 mm) of the connector per TIA/EIA-568 standards.
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 cable length exceeds 100 meters
Why it's wrong here
Ethernet's 100-meter limit is based on signal attenuation over copper; running a cable longer than that degrades the signal below the receiver's threshold, causing link flapping or complete loss of link rather than isolated CRC errors. While marginal attenuation might occasionally produce bit errors, the standard failure mode is a down port, not a steady stream of cyclic redundancy check (CRC) errors. Therefore, this is unlikely when the switch link is otherwise up and functional.
- ✓
The twisted pairs are not properly terminated
Why this is correct
Proper termination requires maintaining the twist of each pair up to the point of insulation displacement; untwisting more than about 13 mm (0.5 inch) ruins the pair's electromagnetic cancellation, allowing crosstalk and signal reflections. Those anomalies corrupt Ethernet frames, and the NIC/switch detects them as cyclic redundancy check (CRC) errors, even though the link remains up. This direct correlation between local termination quality and CRC counters makes it the most likely root cause.
- ✗
The switch port is configured for the wrong speed or duplex
Why it's wrong here
Speed/duplex mismatch is a classic cause of network slowness, but it manifests as late collisions, runts, and frame check sequence (FCS) errors rather than isolated CRC errors. The port's autonegotiation failure itself doesn't directly damage frame data; it causes two devices to transmit at overlapping times, corrupting frames at the physical layer. Since the symptom is specifically CRC errors, this mismatch is not the most probable cause.
- ✗
Electromagnetic interference (EMI) from nearby power cables
Why it's wrong here
Electromagnetic interference (EMI) from power cables can corrupt network signals, particularly when the cable is unshielded and routed parallel to high-voltage lines. But twisted-pair cable is specifically engineered to cancel common-mode noise, and a modem office would require severe, unusual proximity to generate persistent CRC errors. While intermittent CRC counts can sometimes stem from EMI, the direct evidence of improper termination in the workspace is a far more probable and easily validated culprit.
Go deeper
Related to this question
Learn chapter
Home and SOHO Network Setup
Key term
Registered Jack Function 45
An RJ45 connector is the clear plastic plug at the end of an Ethernet cable that connects computers, routers, and switches to form a wired network.
Key term
Local Connector
A local connector is a cable or port used to link a device like a computer to a nearby peripheral or network within the same immediate area.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 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 220-1101 exam.