If a wired computer connects at 100 Mbps where you expected a gigabit, check the negotiated link rate before blaming the internet provider. Test one known-good cable directly between the computer and the router or switch. Then add the wall jack, dock, or intermediate switch back one at a time until the slow link reappears.
Check the negotiated Ethernet link rate
Start by recording the speed shown for the active wired adapter. In Windows PowerShell, run Get-NetAdapter and look at the status and link speed for the Ethernet adapter you are using. Microsoft documents the command in its Get-NetAdapter reference. If several interfaces are present, unplug the Ethernet cable briefly and identify the entry whose connection changes. Reconnect the cable before running the comparison.
The negotiated rate describes the link between the computer and the next device. It is different from the speed of an internet plan or an application. For example, a gigabit link from a laptop to a switch says nothing by itself about the connection between that switch and the router. An internet test combines the local path, the provider connection, and the remote server. Write down the link rate and the actual transfer result separately.
Check what each endpoint supports before looking for a fault. An older router or a small USB adapter may have a 100 Mbps port by design. Some devices have a mixture of port speeds. Match the port number to the hardware manual. If the adapter and the port both support gigabit, keep their usual automatic negotiation settings while you compare cables and paths.
Establish a direct connection with a known cable
Connect the computer directly to a compatible LAN port on the router or switch with a short cable that has already worked at the expected rate. Avoid passing through a wall jack, a dock, or a second switch in the first test if you can. Confirm that the computer is using the Ethernet connection. A laptop with both Wi-Fi and Ethernet enabled can make an internet test hard to interpret if you do not check which interface carries the traffic.
Wait for the link to come up and check the negotiated rate again. If it still shows 100 Mbps, swap to another known suitable port on the same device. Keep the same cable for that test. If the rate changes, compare the two port specifications or check their status in the switch interface where available. If it stays slow, test the cable and port with another computer or adapter that you know supports gigabit.
If a dock or USB adapter is the only Ethernet connection available, record the exact model and check its port rating. Try it directly on another suitable USB port and check that the dock is powered as documented. A gigabit negotiation does not guarantee that the host path can sustain a gigabit transfer. For more on shared USB paths, see our USB-C cable and dock guide.
Add wall jacks and switches back one at a time
Once the short direct path works, reconnect one component at a time. First try the normal patch cable in the same ports. Then add the wall jack and the patch lead at the other end. If the rate falls at that step, try known-good patch leads at both ends before concluding that the in-wall run is at fault. Label the endpoints so you can repeat the test on the same cable rather than guessing which patch-panel port serves the room.
A cable path can be faulty even when an Ethernet light turns on. A poor connection or damaged termination can allow one rate and fail at another. Do not force a faster setting to hide the symptom. Check the plugs and the jacks, and use a suitable cable tester or installer if the problem persists in the permanent run. A basic continuity test can find some wiring problems, but a passing result does not measure every performance characteristic of an installed link.
If your path includes a second switch or mesh unit, check each segment separately. A wired computer connected to a satellite may still send traffic through a wireless uplink. Our mesh backhaul guide explains how to verify the upstream path. If the slow result happens only when traffic crosses that segment, keep the working direct result as your reference.
Verify the repair with a realistic transfer
Repeat the original task after restoring the expected link rate. Copy a file between two known wired devices if available, then test the internet separately if that was the original problem. Use the same file and destination for the comparison and record the result. File transfers also depend on the source and destination storage. A slow disk can hold back a test even when the Ethernet path is working.
Remember the units when comparing results. One gigabit per second equals 125 megabytes per second before overhead. Real applications deliver less, and several devices can share an uplink. If the computer negotiates the expected rate but online play still spikes, use the tests in our ping and packet loss guide to check latency and congestion separately.
Write down the port, cable, and link rate that worked. If the failure only appears after moving furniture or reconnecting a dock, record that sequence too. Try a normal work session before calling the problem fixed. A clean connection immediately after plugging in can still be intermittent, and a repeatable test gives you better evidence if the issue returns.
For example, suppose the same laptop and switch negotiate gigabit with a short cable but 100 Mbps through the living-room jack. Test both removable leads on the direct connection. If each works there and the jack path still falls back, document both wall endpoints and have the permanent run checked. That is stronger evidence than replacing the laptop adapter based on one internet result.
If the slow path carries more than one device, also check which switch port serves as the uplink. A computer can negotiate a gigabit to the nearest switch while every device on that switch shares a slower upstream link. Test a transfer between two devices on that switch and then one that crosses the uplink. If only the second test is slow, look at that upstream connection instead of replacing each computer’s cable. Keep both measurements so you can tell whether a later change improved the local link or the shared path.
Frequently asked questions
Why does Ethernet show 100 Mbps on a gigabit plan?
Check the hardware rating and negotiated speed on each local segment. The internet plan cannot raise a link that negotiated a lower rate.
Should I force gigabit in adapter settings?
Keep the normal automatic settings while troubleshooting. Fix or replace the component that prevents normal negotiation.
Can a switch have ports of different speeds?
Yes. Check the manual and verify the particular port and uplink you are using.
Does a gigabit link mean my internet must be that fast?
No. It describes one local link. The rest of the path and the destination also affect the result.
