SoftEther VPN User Forum

I'm the system administrator of my company's office network which is Windows based. I've installed Softether VPN server on one of the servers to avoid Windows own VPN system. It was very simple and convenient to install and configure it. We use VPN to estabilish secure connections between our field workers home computers and the office network. After some days of normal operation suddenly the VPN connections broke down and couldn't be reestabilished. I figured out that the computer running the SoftEther server application lost internet connection. Only the LAN was accessable from this machine. Any other computer in the network had internet access and LAN also. After several restarts of the network card and the whole machine with no results I decided to set up SoftEther on another computer. I couldn't fix the first machine's internet connection. After few days this first computer finally resolved although I didn't do anything. After some other days of normal operation this issue repeated on the second machine. I directed back the port forwarding to the first machine on which the SoftEther server runned simultaneously and it began to work again. Then after few hours this computer lost internet again. Disabling the firewall on the computers doesn't solve the problem. The network is controlled by a main server which runs Windows Small Business Server operating system. It manages DHCP and DNS. What causes this problem?

It's too bad that nobody replied anything. Anyway, finally I managed to solve the problem.

The router blocked the internet connection of the computer running the SoftEther VPN server software. The router has a DoS-attack protection system and it was active. The protection system banned the computer running the SoftEther VPN server because it sensed, that the SoftEther VPN server behaved like doing a DoS attack.

The SoftEther server was version 2.00, router is a TP-LINK TL-WR740N. The DoS protection system has three filters: ICMP-FLOOD Attack filter, UDP-FLOOD filter, TCP-SYN-FLOOD attack filter. All of these have threshold limits that could be set between 5 - 3600 packets/s. The router used default setup: ICMP-FLOOD Attack filter - 50 packets/s, UDP-FLOOD filter - 500 packets/s, TCP-SYN-FLOOD attack filter - 50 packets/s. I didn't modified any of these just turned off DoS protection and deleted the IP addresses from the ban list.

I post this comment because I think it could be beneficial to share this info that SoftEther VPN server could interfere with the router's DoS protection system.