We pick d.root-servers.net, one of the 13 root servers (1), and ask it about vw-edelmetalle.de and learn that de is delegated to six name servers (2), so we ask l.de.net where we learn that vw-edelmetalle.de is delegated to two name servers, including ns2.fastpark.net (3), so we ask that one and get the following answer:
All of the more than a thousands domains that use the primary name server ns63.rookdns.com use name server group 1 (example: kamelenforum.nl, spartaste.de and dctk.de ). Worth noting is that most of the domains that use name server group 1 use the primary name server ns63.rookdns.com.
The two name servers ns63 and ns64.rookdns.com together
There are more than a thousands domains that use name server group 1.