A few months ago, I wrote about setting up an OpenVPN server on Windows. I was mainly using this to VNC to my workstation, and I noticed some pretty poor performance occasionally. It wasn't that the connection speed was slow -- it was actually dropping the connection almost every minute or so.
At first, I decided that it was the WiFi network I was on. Maybe there was congestion. Or maybe OpenVPN on Windows is just bad. After some research, I found that the problem may have been an incorrect MTU (maximum transmission unit). According to Sonassi's knowledge base, symptoms of incorrect MTU include:
- Slow VPN performance
- Incomplete page load of resources
I decided to give it a shot and identify the correct MTU for my server:
ping -n 1 -l 1500 -f www.example.com
According to the directions, decrease the
1500 value by
10 each time until the ping succeeds. For my workstation,
1470 was the right value.
Next I had to update the MTU for the OpenVPN TAP network adapter.
In the MTU section, put the value for your workstation.
Finally, update your
server.ovpn config and use MTU-40 for your
mssfix. For me, it's
I found this was really useful for fixing the dropped connections. Hopefully it helps your Windows OpenVPN server as well.