Throttled ethernet upload speed in windows 10

Question

I have inconsistent upload speeds on my network, specifically on my Windows 10 machine, over Ethernet.

For reference, the speeds I'm getting over Wi-Fi are:

D: 300 Mbps U: 100 Mbps

But when I do the same test over Ethernet:

D: 300 Mbps U: 50 Mbps

Upload speed drops down by half. It starts at 100 but quickly drops to 50.

I know this is not a hardware issue because of these:

• Tried the same test on a Mac; speeds are the same over Wi-Fi and Ethernet (300/100), using the same cables and router.
• I have Ubuntu on WSL2 on the Windows 10 PC with the issue (aka Linux inside the same Windows machine) and got the expected speeds (300/100) on the same hardware.

The issue is not browser-dependent since I tried Brave and Edge on Windows 10 and Safari and Chrome on Mac. I also tried Ookla's CLI speed test in Windows with the same results (300/50).

This is a clean install; I ensured that no manufacturer software could affect my connection (Motherboard is a ROG Maximus Code XI), or at least I couldn't find any software.

I am not using any antivirus software except for the one that comes with the OS.

Metered connection is disabled.

Disabling Microsoft Defender Firewall gives the same results.

Disabling Virus & threat protection settings give the same results.

I have also toggled every Advanced Setting for my Ethernet Adapter with no difference, also increased buffers to max (2048), and got the same results.

Disabling QoS for the Ethernet adapter makes no difference.

All drivers are up to date.

My router is an Asus RT-AC88U and capable of handling this connection and more.

The motherboard is a ROG Maximus Code XI with an Intel I219-V Ethernet adapter.

Running Windows 10 Pro. Version: 20H2, Build: 19042.868

All Ethernet cables are at least Cat6.

Results are similar on both speedtest.net and fast.com

I have also tried connecting the PC directly to the modem instead of the router with no effect.

Only upload speed is affected; ping, jitter, and download speed behave as expected.

I'm going crazy over this, and I don't know what else to try. I thought one of the Network Adapter settings would give me the expected results, but it didn't, or I couldn't find the right setting.

Any help will be appreciated!

Answer 1

While I don't have the exact answer to my question, I found that different tests give different results; I may actually get 100Mbps upload, but it varies from service to service.

After running tests on different providers, my average speeds are:

D: 291.167 U: 67.065

Some of the providers get to 100Mbps. I think I'm done trying to debug this, it seems to vary a lot, and at best, I can only get an estimate of my real speed. With that said, the lowest speed was 50Mbps, which is not bad at all.

Just for completeness, I also found TCP Optimizer, which helps optimize the Network Adapter settings.

And here are the test results:

|Provider                       |Download|Upload|
|-------------------------------|--------|------|
|Cox                            |296.4   |99.8  |
|speedtest.net.in               |302.11  |91.29 |
|Comparitech                    |323.23  |53.74 |
|https://fast.com/#             |350     |66    |
|https://www.bandwidthplace.com/|190.9   |59.76 |
|http://openspeedtest.com/      |312.4   |71.1  |
|https://speedtest.xfinity.com/ |301.7   |52.6  |
|https://www.speedcheck.org/    |286.98  |59.92 |
|https://speedof.me/            |330.75  |66.94 |
|testmy.net                     |217.2   |49.5  |
|Average                        |291.167 |67.065|