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SoftEther VPN connection loses internet when Number of nTCP connection is 16 or 32 on Windows client - a bug?

Posted: Mon Dec 14, 2020 12:30 am
by coolname
SoftEther VPN connection loses internet when Number of TCP connections is 16 or 32 on Windows client - a possible bug in Windows client or server side

Steps I followed:
* Set up softether server (Ver 4.34, Build 9745, rtm) on CentOS, and client on Windows 7.
* Set the server Maximum Number of TCP connections to 32 on server security policy.
* Set on the Windows client the Number of TCP connections to 32 or 16; Disable UDP acceleration, and disable NAT-T.
* Other settings: Port 443, Direct TCP/IP Connection, Auth Type: Standard Password Authentication (user/pass), Encrypt VPN Session with SSL
* Setup a server entry in Windows client, and connect the Windows client to the remote server.
* In FireFox on Windows accessing any site hangs and eventually errors on network issue; Windows client would sometimes disconnects and reconnect. But there is still no internet after connection is established.
* Disconnect the Windows client and reduce the Number of TCP Connections to 4 or below. Reconnect. The issue goes away and Internet is back. With the setting set to 8, sometimes the issue also shows up. But 16 and 32 would definitely trigger the issue almost every time in my experience.
* Shutdown and restart the softether server software sometimes helps a little. But it doesn’t fix the issue and soon the issue would recur.

* Another likely related issue: with client set to have 8 TCP connections, the Windows client connects. Sometimes, the test result can go very high such as download speed of 400 mbps, but if I disconnect and reconnect the windows client, the speed comes back to normal of ~40mbps and usually stays at around this speed. This seems to happen quite frequently but not all the time. My guess is this might indicate the Windows client is “leaking” such connections and they are not going through the VPN tunnel in the initial connection with much higher speed test result.

Just wanna report the issues as they might be bugs. I wonder if any other folks have also experienced such issues. Please share if so.