hi thanks for all the suggestions.
I started with your remark 'The bottom line is FortiGate's VPN itself is unlikely the cause'
So i setup a simple ftp server, forwarded a port and tested the speed without vpn.
And the speed is the same as I get with vpn.
So it's no VPN issue.
It's also no SMB issue as I have the same result with FTP.
I also tested the speed to another server on the remote network. Same speed so it's no problem with the remote server I was testing with.
I tested the speed between those two servers on the remote network and I get 900mbit/sec so thats also not the problem. So it's also no issue with the duplex settings on this switch I guess? (the switch being the fortigate here for both servers)
The test site and remote site are only 10km away from each other and are with the same ISP. Speed tests on remote site 230/30, on the test site 200/30. I also tested from another site with a different ISP. same result.
No ping loss with vpn on or off.
thats what I got for now. The other suggestions I need to test.
But if anything I tested so far leads to other suggestions I am happy to hear them:)
post edited by bashrael - 2017/07/29 13:53:40