Originally Posted by LeoLinux
I know now that every SSL certificate needs it's own IP address, which means that I would have to buy/rent a new public static IP address and forward it to my already existing static IP address where my ISPconfig is running.
BUT, where can I buy/rent such a public IP adreess?
Your dedicated server / ISP provider will probably rent you some IPs.
Then you should add it to your network card settings (/etc/network/interfaces) and then add it to your ispconfig (panel : management - server - settings - ip list) , then you will be able to choose it from dropdown box at site configuration and generate ssl cert.
Hope this will help you.