We pick j.root-servers.net, one of the 13 root servers (1), and ask it about nic.de and learn that de is delegated to six name servers (2), so we ask z.nic.de where we learn that nic.de is delegated to three name servers, including ns3.denic.de (3), so we ask that one and get the following answer:
Nic.de is a domain controlled by three domain name servers at denic.de having a total of four IP numbers. All four of them are on different IP networks. Incoming mail for nic.de is handled by two mail servers also at denic.de having a total of four IP numbers. Some of them are on the same IP network. Nic.de has one IP number (81.91.170.12), but the reverse is www.denic.de.
There are 14 domains that use the mail server mx2.denic.de.
All of those use the two mail servers mx1 and mx2.denic.de together.
Three of them point to the IP number 81.91.170.12. Worth noting is that three of the host names that point to the IP number 81.91.170.12 use the mail server mx2.denic.de.
The IP number 81.91.170.12
There are about twenty host names that point to the IP number 81.91.170.12.