ns3.tn1.de has one IP number , but the reverse is ns3.inwx.de. c.na-se.de, ns3.n5n.de, ns2.jmsd.de, ns3.onvo.de, ns2.nahl.de and at least 100 other hosts point to the same IP. tn1.de use this as a nameserver. tn1.de is a domain controlled by three nameservers at tn1.de themselves. All of them are on different IP networks. Incoming mail for tn1.de is handled by two mailservers also at tn1.de. They are on different IP networks. tn1.de has one IP number. ns3.tn1.de is hosted on a server in Germany.