CompTIA Network+ (N10-009)Network TroubleshootingMedium
A technician installs a new Cat 6 cable run measuring 150 meters between an IDF closet and a workstation. Users report frequent dropped connections and the switch reports a high number of CRC errors on that port. A cable certifier shows the wire map, NEXT, and return loss all pass. What is the most likely cause of the issue?
- ACrosstalk between adjacent pairs
- BA duplex mismatch on the switch port
- CThe cable run exceeds the maximum specified length for Cat 6 (100 meters)
- DAn incorrect cable category was used
Show answer & explanationAnswer & explanation
Correct answer: C. The cable run exceeds the maximum specified length for Cat 6 (100 meters)
Ethernet over twisted-pair copper cabling (including Cat 6) is specified for a maximum run length of 100 meters. Runs exceeding this limit suffer excessive attenuation and signal degradation, leading to CRC errors and intermittent disconnects, even if wire map and crosstalk tests initially pass.
Why the other options are wrong
- A. Crosstalk was already ruled out by the passing NEXT test.
- B. Duplex mismatch produces late collisions and performance issues, not necessarily tied to a specific measured length.
- D. The cable category (Cat 6) is correct; the issue is length, not category.
Maximum Copper Cable Length
Twisted-pair Ethernet cabling (Cat 5e/6/6a) is limited to a maximum segment length of 100 meters due to attenuation and signal degradation.
- 100 meters includes patch cords plus horizontal cabling.
- Exceeding this causes attenuation, CRC errors, and intermittent drops.
- Solution: use fiber or add a repeater/switch for longer distances.
Memory trick: '100 meters is the copper Ethernet ceiling.'