I recently upgraded my internet plan to get up to 900Mbps speeds. When I run speed tests on my main server, which is a Unifi Dream Machine Pro, I get around 924Mbps as expected. However, on my PC, the max speed I get is just 100Mbps. Looking into it, I noticed that the Ethernet port on my PC is set to Fast Ethernet and Windows shows the connection speed as 100/100Mbps. I’ve tried forcing the port to gigabit speeds in the settings, updated drivers and BIOS, and restarted, but no luck. All my hardware supports gigabit speeds and the cable connected to my PC is Cat 5e, from the same reel as the cable to my Unifi device. What else could be causing my PC to cap at 100Mbps? Any ideas would be appreciated!
4 Answers
Since Windows is showing 100/100 Mbps for the connection speed, it’s often a sign that the network card mistakenly detected or fell back to Fast Ethernet mode. Even if you tried forcing gigabit in properties, sometimes the network adapter or its driver won’t allow forcing speeds that the hardware doesn’t support properly or if negotiation fails. Double-check your NIC driver version on the manufacturer’s website or try uninstalling and reinstalling it. You could also try switching the Ethernet port on your PC or even testing with a USB to Ethernet adapter if available.
First thing I’d check is the physical connection. Even though your cable is Cat 5e from the same reel, since you mentioned terminating it yourself, it’s possible one of the ends isn’t wired correctly or there’s a bad crimp. Gigabit Ethernet requires all four pairs of wires to be properly connected, whereas 100Mbps only uses two pairs. Try re-terminating the cable or swapping it with another known good gigabit cable to see if that fixes the speed cap.
One more thing I can suggest: even though you said your hardware supports gigabit, sometimes the PC’s Ethernet port itself might have an issue or get stuck on 100Mbps. If you’ve updated everything and it still won’t work, testing with a different network card (like a PCIe gigabit card or a USB adapter) is a quick way to see if the problem is hardware-related on the PC. If that fixes it, you can skip the full OS reinstall.
Also worth testing is connecting your PC directly to the modem using a cable you trust. That bypasses the router and can help isolate if the issue is between your PC and the router. Don’t forget to reboot the modem and PC afterward to get a fresh IP. If your PC still only gets 100Mbps directly from the modem, that pretty much confirms it’s the PC side causing the limit.
Thanks, that makes sense! I’ll try swapping cables with my partner’s PC, which is running fine at gigabit, and see if that helps.