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I set up SoftEther VPN server on a VPS on Centos 6.10. Strangely, I can access the server with VPN Server Manager and do whatever I like with it, but when I try to make VPN connection (from the very same notebook) to the server using Windows 10 built-in VPN client and L2TP/IPSec or SSTP protocol, it fails after timeout.

What is puzzling me: - when I put the server HTTPS URL in the browser, it connects (and shows HTTP error 403, which, I suppose, is the correct response). So the connection is not blocked - same for Server Manager - it works - I have another VPN server with different provider, running the same version of SoftEther (4.27.b9666), same OS (Centos 6.10 x64), same configuration (L2TP and SSTP permitted) to which the same Windows PC can make VPN connection without any problem.

The server that I cannot connect to has the following messages in server log:

2018-10-09 20:04:04.274 On the TCP Listener (Port 443), a Client (IP address 86.49.244.0, Host name "ip-86-49-244-0.net.upcbroadband.cz", Port number 53477) has connected.
2018-10-09 20:04:04.274 For the client (IP address: 86.49.244.0, host name: "ip-86-49-244-0.net.upcbroadband.cz", port number: 53477), connection "CID-7" has been created.
2018-10-09 20:04:04.314 SSL communication for connection "CID-7" has been started. The encryption algorithm name is "AES128-SHA".
2018-10-09 20:04:04.345 Connection "CID-7" terminated by the cause "A client which is non-SoftEther VPN software has connected to the port." (code 5).
2018-10-09 20:04:04.345 Connection "CID-7" has been terminated.

What's also strange:

when trying to connect from my office (corporate network, different source IP etc.), connection attempt does not even cause any mention in the server log at all. At the same time I have been sitting on Server Management connection to the very same machine and downloading the logs.

UPDATE

Although it was not working from home, from the office L2TP/IPSec still times out; but when I switch Windows VPN client config to SSTP, it started working.

Maybe I should close and freeze this issue. It could be related to DNS issues (from home) and with protocol/port filtering in the office. Both is relatively difficult for me to verify.

The above server log with "non-SoftEther VPN software" remains unexplained, but it could also be an issue related to configuration. Maybe the server needs to be restarted after new functions are set (in this case "Enable MS-SSTP clone server function" and "Enable L2TP Server Function".

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  • SSTP is heavily reliant on certificates - as it connectes over HTTPS - so you need to make sure you create a certificate on your CentOS box that matches your domain name and install this on your client machine. The certificate is used to make the SSL handshake to allow the SSTP connection process to begin and succeed. E.g. digitalocean.com/community/tutorials/… (STEP 10)
    – Kinnectus
    Commented Oct 10, 2018 at 7:19
  • Well, certificate is not the problem. It doesn't even get to that phase. If certificate was a problem, there would be an explaining error message from Windows (such as "certificate chain ends on root certificate not trusted" etc.). But in my case, strangely, the Windows client did not even make it to the server port. My above example with different IP was coincidence in timing. In fact VPN connection attempt produces nothing in the server log and times out.
    – Jindrich Vavruska
    Commented Oct 10, 2018 at 7:34
  • Are you also running a webserver (Apache) on your VPS that is using HTTPS?
    – Kinnectus
    Commented Oct 10, 2018 at 7:39
  • No. On this machine it hasn't even been preconfigured (and not present in the initial setup). On the other one I had to kill and disable Apache because it occupied port 443 :)
    – Jindrich Vavruska
    Commented Oct 10, 2018 at 7:50
  • Can you post your output for sudo netstat -plnt | grep ':443'?
    – Kinnectus
    Commented Oct 10, 2018 at 8:00

1 Answer 1

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There seem to be two different problems.

Problem 1: after initial setup of the server, the server is up, server admin added the first Virtual Hub and enabled SSTP and L2TP. However, client cannot connect.

SOLUTION: Obviously, the VPN server needs to be restarted (on the server console service vpnserver restart. Indeed, restart solved the problem with SSTP not connecting.

Problem 2: L2TP connection from Windows did not work in corporate network. Since in the same situation SSTP works, it must be due to protocol and/or port filtering in the corporate network firewall.

SOLUTION: Obviously, switching the VPN configuration to SSTP solves the problem.

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