We pick e.root-servers.net, one of the 13 root servers (1), and ask it about ns2.denic.de and learn that de is delegated to six name servers (2), so we ask f.nic.de where we learn that denic.de is delegated to three name servers, including ns2.denic.de (3), so we ask that one and get the following answer:
Ten of them use the two mail servers mx1 and mx2.denic.de together, hereafter referred to as "mail server group 1", (example: deniceg.de, denic.de and nic.de ).
Three of them point only to the IP number 81.91.170.12.
The three name servers ns1, ns2 and ns3.denic.de together
There are about twenty domains that use name server group 1.
Ten of those use mail server group 1.
Three of them point only to the IP number 81.91.170.12.
The IP number 193.171.255.36
All of the one host names that point to the IP number 193.171.255.36 point only to that ip number.