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How to increase TCP Window Size on Windows 10

Tassadar

6/7/23, 5:55 PM

I think my problem is easy to explain: I need to increase TCP Window size on a Windows 10 machine but i'm unable to.

I've create a SFTP Server on a Windows 10 machine and I access to it via other PC in another location on the same city. Both locations have optic fiber connections with simetric 600 megabits/s.

Using both machines on same lan I get 48 megabytes per second, but when moving to wan (over the optic fiber) it top at 8,5 - 10 megabytes/s.

Accoding to my calculations it happends becouse the latency between both coneections and tcp window size is configured at 64k.

On previous Windows version it can be changed via registry but now it doesn't work. Now it's supposed to be changed using autotuning level, I've change it from normal to highly restricted and even experimental using SG TCP Optimizer but speed is the same.

Thanks for reading

EDIT: According to this link:

https://docs.microsoft.com/en-us/troubleshoot/windows-server/networking/description-tcp-features

I've create the key "Tcp1323Opts" on the registry, under "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Tcpip\Parameters" and then assign value "3 to it.

Now when I open a PowerShell window and run:

"netsh interface tcp show global"

I get that RFC1323 is enabled and before was disabled, so the creation of the new key in the registry is ok. The problem is the speed is the same.

I didn't know if I had to create this key in the computer where SFTP is installed or the one who send data, so I created the key on both.

I think I have to set an scale factor or scale value acoording to the link, but I don't know where to assign it.

I feel I'm near of the solution but I need some help.

Regards

369

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windows

Greg Askew

6/7/23, 6:30 PM

64k is the maximum window size. To increase this further, Tcp1323Opts needs to be used to enable window scaling. https://docs.microsoft.com/en-us/troubleshoot/windows-server/networking/description-tcp-features

Tassadar

6/7/23, 7:06 PM

Many thanks for your message. Believe me or not, I came to tell I had found that link and tried, then you was reccomending me the same URL xD. I've edit first message and explain what I've done, I'd thank you a lot if you can give me some advice

Greg Askew

6/7/23, 7:30 PM

When you perform a capture during the three way handshake, is the window scale being negotiated, and what is the size? What value is specified for `HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters!TcpWindowSize`

Tassadar

6/7/23, 7:41 PM

Honestly, I don't know what the 3 way handshake is. In the registry there is no key called "TcpWindowSize" under "HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters". I suppose the first think I have to do is monitor the actual scale value but don't know to to. Thanks

Zac67

6/7/23, 7:42 PM

Receive window scaling is active by default on Win10, no need to explicitly activate.

Tassadar

6/7/23, 7:51 PM

Thanks for your comment, Zac67. I don't know if it's active by default or not, what I know is the speed on both fiber connections is higher than 500 megabits per second, that should give at least 30 megabytes per second. The latency is making me impossible to get the speed and I know becouse Ive simulate the latency in the lan (computers in the same room) and when I increase latency speed goes down. Regards

user996142

6/7/23, 8:02 PM

What is your ping? And also check bandwidth with ``iperf3`` to see if increasing number of threads affects bandwidh.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: How to increase TCP Window Size on Windows 10

TH: วิธีเพิ่มขนาดหน้าต่าง TCP ใน Windows 10

RO: Cum să măriți dimensiunea ferestrei TCP pe Windows 10

RU: Как увеличить размер окна TCP в Windows 10

VI: Cách tăng Kích thước cửa sổ TCP trên Windows 10

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