[Openvpn-users] TCP throughput problem with openvpn on windows - resolved

[Thomas Glanzmann <sithglan@xxxxxxxxxxxxxxxxxxxx>]

Hello,
I had the problem that I got only 200kb/s from a windows machine through
an openvpn tunnel. But when I opened 4 connections I got 800 kb/s but
only 200kb/s with one connection. The problem was that the TCP Window on
the windows machine was to small and the ACKs were to slow, so that the
connection was around 200kb/s. I saw that also on ethereal when I looked
at the TCP connection. => [TCP WINDOW FULL]

I solved the issue on windows by setting these two registry entries:

        # This enables TCP Window Scaling (DWORD)
        HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Tcp1323Opts=1

        # This makes the default TCP Window bigger (DWORD)
        HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\TcpWindowSize=65355

See also:

http://proj.sunet.se/E2E/tcptune.html
http://www.speedguide.net/read_articles.php?id=157

Sincerely,
        Thomas

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