I'm at my wit's end here! I recently built a new rig, but I'm stuck with Ethernet speed capped at 100 Mb/s and Wi-Fi barely hitting 120 Mb/s. Meanwhile, every other device on my network, including another PC, laptop, and phone, are cruising between 400-600+ on Wi-Fi and 650-700+ on Ethernet, all using the same cables and modem port!
I've spent over six hours troubleshooting and tried numerous solutions: swapping multiple brand-new Cat-6 cables, connecting directly to the modem (Spectrum EN2251 DOCSIS 3.1), power-cycling the modem, updating the BIOS, clearing CMOS, fresh installs of Windows 11 and Pop!_OS, and experimenting with various Realtek drivers. I even disabled Green Ethernet and forced 1.0 Gbps Full Duplex, yet nothing seems to change the dreadful speeds.
Here's my build for reference:
- AMD Ryzen 9 9900X3D
- MSI MAG X870E Tomahawk WiFi (Realtek RTL8125B 2.5Gb Ethernet, Qualcomm FastConnect 7800 Wi-Fi 7)
- 64GB G.Skill Trident Z5 Neo DDR5-6000
- Gigabyte RTX 5080 Aorus Master
The Realtek NIC just won't negotiate over 100 Mb/s, and the Wi-Fi isn't much better. Other devices on the same setup are fine, which is so frustrating! I really want to resolve this before needing to return any parts. Could there be a hardware issue with the RTL8125B? Any advice would be greatly appreciated!
5 Answers
I had a lot of trouble as well, and eventually replaced my motherboard with a basic one and it fixed the issues. Maybe you could consider that option—there are affordable boards that can handle the performance you need without breaking the bank.
If your NIC isn’t linking at gigabit speeds while others are using the same cables, it sounds like you might have a bad NIC. Honestly, I’d suggest just grabbing a PCIe NIC; it’s a quick fix and should get you sorted out. RMAing the board might take too long, and spending about $30 on a new card is definitely easier!
Have you thought about updating your chipset drivers? Also, since you mentioned it’s an MSI board, skip the Killer network software if you were thinking about installing that. Sometimes it can conflict with other drivers.
I've noticed that when I'm connected through the motherboard, my Windows settings show Link Speed as 100/100. But when I use a dongle, it jumps straight to 1000/1000, and my speeds are spot on. Seems like there’s definitely something up with your onboard NIC.
Check your NIC’s settings in Device Manager. Make sure it’s set to 'Auto Negotiation' for the best speed. Also, confirm it’s not locked to 2.4GHz only. You can find that under the properties tab for your NIC. If all else fails, consider getting a new NIC or even a USB Wi-Fi dongle to see if that helps! Also, inspect the Ethernet port for any damaged pins—one faulty pin can drop your speed to 100 Mbps!
Funny you mention that, I used a USB-C to Ethernet dongle and managed over 600 Mbps with that!
Totally agree! I had a similar issue with my old gaming rig. After trying all sorts of troubleshooting, I bought a 2.5 Gbps PCI card and that did the trick. Now I get my full speeds without issue!