I have ispconfig3 in opensuse 11.3, my question is: can I have ns1.website1.com and ns1.website2.com with the same IP? regards
Theoretically yes, but some registrars might refuse to accept your nameservers as they are on the same IP. In addition to that, you lose high-availability of your DNS service, because if the server fails, you have no DNS server on another server that can take over.