Extreamly slow Upload speed in Windows (all other OS's on network are fine)

Question

I've been having this issue since at least January 2021 on my entire fleet of Windows devices. I first noticed it when my offsite backups stopped completing in time.

Upload speed in Windows is being throttled by something. Download speed is unaffected.

WAN is 2Gbps symmetrical. My ISP (Washington State K-20 Telecommunications Network) confirmed that their circuit is not the cause and is capable of 1800 Mbps symmetrical throughput. Distance is a factor, as I can get 400Mbps to my local telco (which isn't my IPS). Going past a few hundred kilometers it drops to 30-70Mbps. There is an initial burst, but drops quickly.

I have an HPE/Aruba network and a Sophos XG 310 v2 running SFOS 18.0.4 MR-4. If I plug a client directly into my 10Gbit fiber before my firewall, I can get acceptable speeds on Windows. I haven't been able to find any setting in Sophos XG to tweak that would make any difference. Local iPerf3 tests ruled out my core router/switch/datacenter.

All tests run from Hyper-V guests on Server 2019 Datacenter running on HPE ProLiant DL360 Gen10 hardware.
Windows Server 2019 Datacenter speed tests:

Linux (CentOS 8) speed tests:

Speedtest by Ookla  
  
     Server: Comcast - Seattle, WA (id = 1782)  
        ISP: Washington State K-20 Telecommunications Network  
    Latency:     3.93 ms   (0.16 ms jitter)  
   Download:   915.29 Mbps (data used: 1.2 GB)  
     Upload:  1537.96 Mbps (data used: 1.8 GB)  
Packet Loss: Not available.  
 Result URL: https://www.speedtest.net/result/c/c4bca417-e246-4f46-964a-c4291e4a3914  

Speedtest by Ookla  
  
     Server: Comcast - Sacramento, CA (id = 9436)  
        ISP: Washington State K-20 Telecommunications Network  
    Latency:    24.65 ms   (0.13 ms jitter)  
   Download:  1232.96 Mbps (data used: 1.7 GB)  
     Upload:  1007.46 Mbps (data used: 1.3 GB)  
Packet Loss:     0.4%  
 Result URL: https://www.speedtest.net/result/c/21032a9c-8285-44fe-aadf-ad4dc3d90428  

OS affected for me:

• Windows 10 2004
• Windows 10 20H2
• Windows 2016
• Windows 2019

All devices are fully updated, firmware included.

I've tweaked:

• Limit reservable bandwidth
• AV
• Safe mode boot
• Domain and non-domain computers
• autotuning
• Interrupt Moderation
• Receive Side Scaling
• TCP Congestion Control
• Large Send Offload

I've tried the following hardware:

• Dell Optiplex 7040
• HP Elitebook 840 G5
• HPE ProLiant DL380 Gen10
• HPE ProLiant DL360 Gen10

These OS' are fine:

• ChromeOS
• Android
• MacOS
• iOS
• Linux (CentOS, HyperV)

This is a continuation of https://learn.microsoft.com/en-us/answers/questions/89768/slow-wired-upload-speed-vs-linux-on-same-hardware.html

Answer 1

after so many tries etc. what fixed it for me was to se my MTU to 1380 i have read that my provider work best with it at the 4G - 5G. so now it works perfectly