220-1101 Hardware and Network Troubleshooting Practice Question
A technician runs a new Cat6 Ethernet cable between a switch in the server room and a workstation in an office. The cable run is approximately 120 meters long. The workstation shows a 'Network cable unplugged' error and the switch port LED does not light. The technician confirms the cable is properly terminated with T568B on both ends and the switch port is enabled. Which of the following is the MOST likely cause of the issue?
⚠ Common exam trap
The trap here is that candidates often overlook the 100-meter maximum segment length for twisted-pair cabling and instead focus on termination issues or interference, but the specific symptom of a completely unlit port LED points to a physical layer failure caused by excessive attenuation.
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 cable length exceeds the maximum allowable segment length
The maximum segment length for a Cat6 Ethernet cable is 100 meters (328 feet) for reliable 1000BASE-T operation. At 120 meters, the signal attenuation exceeds the IEEE 802.3ab specification, causing the link to fail. The 'Network cable unplugged' error and unlit switch port LED indicate a physical layer issue, which is most likely due to the excessive cable length.
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 the maximum allowable segment length
Why this is correct
The 100-meter limit for Ethernet over twisted-pair is a hard physical-layer constraint set by the TIA/EIA-568 standard. At 120 meters, attenuation and propagation delay accumulate to the point where the receiving PHY can no longer reliably decode the signal, so the switch will fail to establish link. Even with high-quality Cat6 cable, exceeding the segment length causes the link to be absent or unstable.
- ✗
Electromagnetic interference from nearby power cables
Why it's wrong here
Electromagnetic interference from nearby power cables would typically produce a symptom of intermittent errors, CRC mismatches, or late collisions rather than a complete absence of link. Cat6 cable is designed with tight twisted pairs to reject common-mode noise, and if interference were severe enough to kill the link, it would first cause throughput degradation and error counters to climb. The fact that the run is exactly over the length limit makes attenuation the dominant cause, not EMI.
- ✗
The switch does not support auto-MDIX
Why it's wrong here
Auto-MDIX is only necessary when connecting two identical device types, such as a switch to a switch, because both would use the same pair to transmit. For a standard switch-to-host connection, the switch's MDI-X port already performs the crossover internally, so a straight-through cable works even with auto-MDIX disabled. Therefore, the absence of auto-MDIX cannot explain a complete link failure at this distance.
- ✗
A poor crimp on one of the RJ45 connectors
Why it's wrong here
A poor crimp on an RJ45 connector could prevent link establishment, but the technician verified the terminations with a cable tester, confirming proper pinouts and continuity. In any case, a bad crimp usually produces a specific symptom such as a link that runs at lower speed, drops packets, or is intermittent, not a total failure caused by distance. Given that the run length is 20 meters beyond the specification, the distance alone is a simpler and more complete explanation.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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