thanks for the quick reply. i looked into it and found a solution after a bit trial and error
this is how my /etc/apache2/ports.conf looks like:
# SSL name based virtual hosts are not yet supported, therefore no
# NameVirtualHost statement here
but after the restart of apache i had some warnings. so i searched the apache manual once again. and this is what i came up with:
for this to work, all the vhost's >must< match the NameVirtualHost, so i had to edit all the vhosts in /etc/apache2/sites-available so that they would have something like <VirtualHost 18.104.22.168:80> instead of <VirtualHost *:80>
then the warnings disappeared, so i guess there should be editing to the vhosts after all.
so, the new question is:
will ispconfig allow those changes or will they be reverted to their original state at some point? is there something more to be done?