My desktop gets more than 300 Mbps over Wi‑Fi on my iPhone, but the same network only reaches about 20 Mbps over Ethernet. I've tested multiple cables, including Cat6 and Cat7, and tried a different network, so the cables don't appear to be damaged. I've also updated the Ethernet drivers and set the adapter to 1 Gbps full duplex. What else could be causing the wired connection to be so slow?
4 Answers
Check the router as well. Quality-of-service rules, parental controls, device profiles, or bandwidth limits can affect one wired device without affecting your phone. Make sure the computer is recognized as a normal device and isn’t assigned to a restricted or guest profile. It’s also worth testing with QoS temporarily disabled.
Run the speed test with the same test server on both devices and make sure no downloads, cloud backups, VPNs, or security scans are using the desktop’s connection. If Ethernet still tops out around 20 Mbps after confirming a 1 Gbps link, test with a different router port or a separate USB/PCIe Ethernet adapter to determine whether the motherboard’s network hardware is the problem.
A Windows network reset may clear up a broken adapter configuration. Search Windows Settings for Network reset, run it, and restart the computer. You’ll need to reconnect to the network afterward. Also check the adapter’s advanced properties for Speed & Duplex; Auto Negotiation is usually best, though 1.0 Gbps Full Duplex can be tested if both ends support it.
First check the actual negotiated link speed rather than only the adapter setting. In Windows, open the Ethernet connection status and look for Link speed. It should show 1.0 Gbps if the network adapter, router port, and cable are negotiating properly. If it shows 100 Mbps or 10 Mbps, try another router port, reinstall the motherboard’s LAN driver, and check whether the adapter or port is damaged.
I already tried updating the Ethernet driver and manually selecting 1 Gbps Full Duplex, but I’ll check the negotiated link speed and try a network reset.