We pick b.root-servers.net, one of the 13 root servers (1), and ask it about 253.229.72.77.in-addr.arpa and learn that in-addr.arpa is delegated to six name servers (2), so we ask d.in-addr-servers.arpa where we learn that 229.72.77.in-addr.arpa is delegated to three name servers, including slave.gbg.netnod.se (3), so we ask that one and get the following answer: