I'm really at my wits' end here. I've spent over six hours trying to fix my brand-new PC, but I can't get the Ethernet to connect past 100 Mb/s, and the Wi-Fi barely reaches 120 Mb/s. This is frustrating since all my other devices on the same network easily hit speeds of 400-600+ Mb/s for Wi-Fi and 650-700+ for Ethernet using the exact same cables and modem port. Here's what I've done so far:
- Tried three different brand-new Cat-6 cables.
- Plugged directly into the modem (Spectrum EN2251 DOCSIS 3.1).
- Fully power-cycled the modem (power and coax).
- Updated and flashed the BIOS.
- Cleared CMOS and discharged the motherboard.
- Installed both Windows 11 and Pop!_OS fresh on metal.
- Experimented with all Realtek drivers: Windows default, MSI's latest (v10.63), and an older version.
- Disabled features like Green Ethernet and Auto Disable Gigabit.
- Forced 1.0 Gbps Full Duplex but still no change.
- Used different ports and devices; every other one works fine.
Here's a bit about my build:
- AMD Ryzen 9 9900X3D
- MSI MAG X870E Tomahawk with Realtek RTL8125B 2.5Gb Ethernet
- Qualcomm FastConnect 7800 for Wi-Fi 7
- 64GB DDR5 RAM
- Gigabyte RTX 5080 Aorus Master
The Realtek NIC just won't negotiate beyond 100 Mb/s despite the cables being fine. Wi-Fi lags too, capping around 110-120 Mb/s which is underwhelming for such a modern chip. I'm at a loss and really want to enjoy this rig without facing an RMA. Has anyone else had issues with the RTL8125B? Any suggestions would be greatly appreciated!
5 Answers
I had a similar issue and found that when using USB-C to Ethernet dongles, I hit my desired speeds. It might be worth a shot to see if that works better for you!
I ended up replacing my motherboard to fix similar issues. I went for a budget one, and that solved my speed problem. Might not be ideal, but just something to consider if all else fails.
Double-check your NIC settings in Device Manager. Make sure it's set to "Auto Negotiation" and that it's not limited to 2.4GHz Wi-Fi. If all else fails, a USB Wi-Fi dongle or a new NIC card might be worth trying, especially if there are any damaged pins in the ethernet port.
Have you checked the chipset drivers? Sometimes a simple update can fix these issues. Oh, and if you're using MSI, avoid the Killer network software—it can mess things up. Just a thought!
It sounds like your NIC might be faulty. If other devices can link at gigabit speeds with the same cables, then trying a PCIe NIC could be a quick fix! It's probably easier than going through the whole RMA process. I’ve had great luck with them; they're usually inexpensive too!
Thanks for the tip! I’ll make sure to check those drivers and avoid the Killer software.