To be a bit pedantic, you don't actually resolve the ip address itself. A reverse dns lookup actually just does a lookup of {the ip address with octets reverse

To be a bit pedantic, you don't actually resolve the ip address itself. A reverse dns lookup actually just does a lookup of {the ip address with octets reversed}.in-addr.arpa: > host 216.58.208.238 238.208.58.216.in-addr.arpa domain name pointer par10s22-in-f14.1e100.net. You can actually look that up directly too: > dig +short ptr 238.208.58.216.in-addr.arpa par10s22-in-f14.1e100.net. When an isp gets a ip allocation, they specify the nameservers to use, and are responsible for that "subdomain" of the in-addr.arpa domain. If you trace the full resolve, it first goes to the root .in-addr.arpa servers, then arin.net nameserver, then finally you end up at: ;; AUTHORITY SECTION: 208.58.216.in-addr.arpa. 86400 IN NS ns3.google.com. which will return the actual ptr record.