Can I use the same vps (second dns server) to connect to multiple the perfect server installs? Or one second dns per the perfect server inatall?
There is one other solution though that just came to my mind. ISPConfig supports two types of DNS mirroring, the one where ISPConfig is mirroring the DNS records will not work. But you can create slave DNS records on that server, for this type of record it does not matter which server is the master, not even if it runs ISPConfig.