Direct answer
A wrong result requires checking inputs, mode, calibration and output separately; a working control path can still be configured for the wrong state. For gigabit Ethernet link speed, first inspect negotiated speed and connect a known Cat5e+ cable directly between known gigabit ports.
What this covers
- gigabit Ethernet link speed with this exact failure state
- Diagnosis across device capability versus cable pairs, wall jack, switch and power saving
- Customer-accessible observation, settings and external components
What it does not cover
- ×A displayed manufacturer error code with a different documented meaning
- ×Live electrical, sealed-system, internal battery-cell or gas repair
- ×A claim that every model exposes identical controls
Capture the exact failure state
ReversibleWrite down the selected mode, input conditions and the exact unexpected output. Expected behavior: negotiate 1000 Mbps or higher through every cable pair and port.
Isolate the component boundary
ReversibleInspect negotiated speed and connect a known Cat5e+ cable directly between known gigabit ports. Use a known reference input or manufacturer test and compare the result. Boundary to separate: device capability versus cable pairs, wall jack, switch and power saving.
Correct only the proven cause
ReversibleReplace the segment or port that falls to 100 Mbps. Correct the setting, calibration or component proven by that comparison.
Verify and stop safely
ReversibleRepeat with the reference and a normal real-world case. Stop for wet, pinched, hot or visibly damaged cabling/equipment.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Exact questions
Common follow-ups
What should I check first when gigabit Ethernet link speed has this problem?+
Inspect negotiated speed and connect a known Cat5e+ cable directly between known gigabit ports.
Why not factory-reset immediately?+
The useful boundary is device capability versus cable pairs, wall jack, switch and power saving. A reset can erase state without proving which side failed.
When should I stop troubleshooting?+
stop for wet, pinched, hot or visibly damaged cabling/equipment.
Answer for the exact device and software version shown above.