We pick i.root-servers.net, one of the 13 root servers (1), and ask it about arpa.umbria.it and learn that it is delegated to six name servers (2), so we ask m.dns.it where we learn that arpa.umbria.it is delegated to two name servers, including dns1.perusia.it (3), so we ask that one and get the following answer:
Arpa.umbria.it is a domain controlled by two domain name servers at perusia.it. Both are on different IP networks. Incoming mail for arpa.umbria.it is handled by two mail servers at umbria.it. Both are on the same IP network.