Question Persistently low network speeds on PC with a 1 Gbps service ?

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djpleiades

djpleiades

Mar 11, 2025
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Hello everyone,

I'm experiencing a frustrating issue with my PC's network speeds and could really use some advice. Despite upgrading to a 1 Gbps service tier from my ISP, my PC is only getting around 300 Mbps, whether connected via Ethernet or Wi-Fi. In contrast, a mobile device on the same network reaches about 800 Mbps down via Wi-Fi.

Details:

  • Adapter Model: Realtek PCIe GbE Family Controller
  • Motherboard: Gigabyte B450M DS3H wifi
  • Operating System: Windows 10
  • Driver Version: 10.68.815.2023
  • Modem: ET2251
  • Router: SBE1v1k
  • Issue Description: My PC's download speed is stuck around 300 Mbps on both Ethernet and Wi-Fi, while upload speeds are fine and reach the full expected performance.
Troubleshooting Done:

  • Updated drivers for the Ethernet adapter.
  • Tested different Ethernet cables and ports.
  • Reset network settings and verified adapter configurations in Device Manager.
  • A technician from my ISP checked and confirmed that the modem does indeed receive the full 1 Gbps speed. They replaced the router, which was already new, but no change.
  • Contacted Gigabyte support for the motherboard; tried updating drivers, disabling Windows auto-tuning, etc., with no improvement.
  • Tested the modem directly to pc, speed was still slow
  • Change Speed & Duplex settings off Auto to 1.0 Gbps Full Duplex
I've reached out to Realtek given the suspected issues might be with the Ethernet adapter, but I wanted to see if anyone here might have insights or suggestions on what else I could try.

Thanks in advance for your help!
 
Last edited:
djpleiades said:
Hello everyone,

I'm experiencing a frustrating issue with my PC's network speeds and could really use some advice. Despite upgrading to a 1 Gbps service tier from my ISP, my PC is only getting around 300 Mbps, whether connected via Ethernet or Wi-Fi. In contrast, a mobile device on the same network reaches about 800 Mbps down via Wi-Fi.

Details:

  • Adapter Model: Realtek PCIe GbE Family Controller
  • Motherboard: Gigabyte B450M DS3H wifi
  • Operating System: Windows 10
  • Driver Version: 10.68.815.2023
  • Modem: ET2251
  • Router: SBE1v1k
  • Issue Description: My PC's download speed is stuck around 300 Mbps on both Ethernet and Wi-Fi, while upload speeds are fine and reach the full expected performance.
Troubleshooting Done:

  • Updated drivers for the Ethernet adapter.
  • Tested different Ethernet cables and ports.
  • Reset network settings and verified adapter configurations in Device Manager.
  • A technician from my ISP checked and confirmed that the modem does indeed receive the full 1 Gbps speed. They replaced the router, which was already new, but no change.
  • Contacted Gigabyte support for the motherboard; tried updating drivers, disabling Windows auto-tuning, etc., with no improvement.
I've reached out to Realtek given the suspected issues might be with the Ethernet adapter, but I wanted to see if anyone here might have insights or suggestions on what else I could try.

Thanks in advance for your help!
Click to expand...
The WiFi adapter is only a 1x1 AC so that limits it to 433Mbps. When figuring in overhead, 300Mbps is pretty good.

The Ethernet is a different problem. That should be able to handle full speed. Does the Ethernet connect to a switch or directly into the modem? Are you Ethernet setting in Windows set to 1Gbps Full Duplex? Have you updated the Ethernet driver?
 
jeremyj_83 said:
The WiFi adapter is only a 1x1 AC so that limits it to 433Mbps. When figuring in overhead, 300Mbps is pretty good.

The Ethernet is a different problem. That should be able to handle full speed. Does the Ethernet connect to a switch or directly into the modem? Are you Ethernet setting in Windows set to 1Gbps Full Duplex? Have you updated the Ethernet driver?
Click to expand...
Thank you for your insights!
For the Wifi that makes sense given the limitations of the adapter. I appreciate the clarification on that front.

Regarding the ethernet, I'm still trying to troubleshoot why im not achieving full speeds:

Connection path: The ethernet cable connects to my router from the modem, and from the modem to PC. There is no switch involved in the setup
Ethernet settings: I have manually set the ethernet adapter settings in Windows to 1Gbps full duplex to ensure its not auto-negotiating to a lower speed.
Driver updates: I have updated the ethernet driver to the latest version available from Gigabyte's site

Despite these settings, I'm still only getting around 300Mbps, which is puzzling. Do you think there could be any other settings in windows that could be limiting the ethernet speed? I dont think any external hardware is at fault here.
 
Likely modem problem. What's your "exact" modem brand / model?

Best if you can post a picture of the modem's label/sticker.
 
Last edited:
cruisetung said:
Likely modem problem. What's your "exact" modem brand / model?

Best if you can post a picture of the modem's label/sticker.
Click to expand...
Thank you for your response!
To clarify, the modem itself appears to be recieving the full 1Gbps speed from the ISP. A technician from my isp tested the connection at the modem and observed speeds of approximately 1035 Mbps indicating that the modem and incoming service to not seem to be the issue.

Here is the exact model of the modem and router:
Modem Brand/Model: Spectrum ET2251
Router Model: Spectrum SBE1v1k

I've tried connecting my PC directly to the modem, bypassing the router entirely, and I'm still observing the same low speeds of around 300 Mbps. Additionally, testing the network speed on my phone via the same router's wifi results in speeds of up to 800 Mbps down. This further supports the notion that the issue is likely not with the modem or router, but localized to my PC.
 
Looks like the motherboard comes with cFosSpeed Internet Accelerator Software?

https://www.gigabyte.com/Motherboard/B450M-DS3H-WIFI-rev-14/support#support-dl-utility

Uninstall it if it's installed on the system, then reboot. These so called accelerator or optimizer usually causes a lot of problems.

Btw, since it's realtek gbe adapter, it should be support natively by Windows, there is no need to install driver from gigabyte in most cases.
 
Last edited:
cruisetung said:
Looks like the motherboard comes with cFosSpeed Internet Accelerator Software?

https://www.gigabyte.com/Motherboard/B450M-DS3H-WIFI-rev-14/support#support-dl-utility

Uninstall it if it's installed on the system, then reboot.
Click to expand...
Thank you for your suggestion about the cFosSpeed software. I checked my system, and it appears this software was never installed, so its not contributing to the issue.

Heres an update on what else I've trie so far:

Safe mode Network test: I conducted speed test in safe mode with networking to ensure minimal background processes were affecting the network, and unfortanetely the speeds were still around 320Mbps, similar to normal conditions.
System File Check: I ran an SFC scan which did find and repair some corrupted Windows files, However there was no improvement in network speed after the repair and restart.

These steps seem to rule out software condlicts and system file corruption as the source of the problem. Given all this, the consistent speed around 300Mbps suggets there might be a hardware limit or configutation issue that I'm still missing.

Do you have any further suggestions on what might be causing this limitation or additional tests I could try to diagnose this issue further?
 
cruisetung said:
You also reset the network before like suggested here, right?

https://smart-help.superloop.com/hc...set-network-settings-on-Windows-10-Windows-11

Running out of my ideas.
Click to expand...
Thank you for the suggestion to reset the network settings. I followed the instructions provided and reset the network. Unfortunately, even after the reset, the speed has not improved and remains about 300 Mbps.

Given all these efforts, the speed issue persists, indicating it might be something more complex, possibly hardware-related. If there are any other advanced settings or diagnostic steps you could suggest, I would greatly apprecaite it. Alternatively, I might consider using an external network adapter to see if the issue is with my current network card.
 
cruisetung said:
I also considered suggesting external non Realtek usb adapter (ASIX for example), but you said wifi was also limited.

Have you considered upgrading to Win11?

==

Oops, your wifi was limited because it's chipset limitation.
Click to expand...
Thanks for the suggestions!
I'm looking into options for external Ethernet adapters, I appreciate the suggestion!
Regarding upgrading to W11, I checked my compatibility, and it does not meet the requirements.
 
@djpleiades

1. Regarding:

"Connection path: The ethernet cable connects to my router from the modem, and from the modem to PC. There is no switch involved in the setup"

Not sure about your description - the expected connection path being as shown in the following line diagram (where ---> represents an Ethernet cable):

ISP === (Coax, DSL, fiber) ===> Modem ----> [WAN Port] Router [LAN ports] ---> wired devices and ~~~> wireless devices.

If the modem is actually a combination modem/router then the modem's router functions (DHCP) need to be disabled.

Feel free to edit and correct my line diagram as necessary.

2. Ensure that only one network adapter (either wired or wireless) is enabled on computer in question - not both network adapters at the same time.

3. Speed and Duplex should be set to Auto.

4. Run "ipconfig /all" (without quotes) via the Commmand Prompt. Post the full results. You should be able to copy and paste it all with no need to retype everything.

There are some other things that can be done.

However, the first objective is to establish the current connections and network related configuration settings.
 
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