We pick f.root-servers.net, one of the 13 root servers (1), and ask it about mobile.de and learn that de is delegated to six name servers (2), so we ask s.de.net where we learn that mobile.de is delegated to two name servers, including dns47-2.mobile.de (3), so we ask that one and get the following answer:
Mobile.de is a domain controlled by two domain name servers at mobile.de themselves having a total of four IP numbers. Two of them are on the same IP network. Incoming mail for mobile.de is handled by two mail servers also at mobile.de having a total of four IP numbers. Two of them are on the same IP network. Mobile.de has four IP numbers (91.211.75.176, 2001:67c:2d0:4200::25, 2001:67c:2d0:4300::25, 194.50.69.176). Two of them are on the same IP network.
The two name servers dns45-2 and dns46-2.mobile.de together
Three of the seven domains that use the two name servers dns45-2 and dns46-2.mobile.de together, hereafter referred to as "name server group 2", point to the two IP numbers 91.211.75.154 and 194.50.69.154 together.
The two mail servers mail46-1 and mail47-1.mobile.de together
Six of the about twenty domains that use mail server group 1 point only to the IP number 194.50.69.144.