We pick d.root-servers.net, one of the 13 root servers (1), and ask it about 2.8.123.233.in-addr.arpa and learn that in-addr.arpa is delegated to six name servers (2), so we ask a.in-addr-servers.arpa where we learn that 233.in-addr.arpa is delegated to four name servers, including a.iana-servers.net (3), so we ask that one and get the following answer: