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 18.104.22.168, 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: 22.214.171.124, 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.
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".