As explained in the section on DNS, domains can be mapped to IP-addresses using A- and AAAA-records. However, the reverse is also true; an IP-address can be pointed to a domain name. This is accomplished through reverse lookup using PTR (pointer)-records. PTR-records appear slightly different to normal IPs. For example, the IP of example.com would be represented by 10.43.0.192.in-addr.arpa. Just like domain names, this too can be split up into sections (or zones) depending on authoritative responsibility. If you query the root-servers about ‘10.43.0.192.in-addr.arpa’, they will reply with whatever information they have available to them (in this case most likely by pointing you to the ARIN’s servers for the 192.in-addr.arpa-zone).
You will then continue downwards, following the path, by querying those servers for information on 0.192.in-addr.arpa (or whatever the next zone is comprised of). Ultimately, you will reach the servers handling the zone file for the full IP, and the PTR will be revealed to you through an authoritative response ( → www.example.com).
Enter the IP you want to perform these steps on above (or use the tool by manually clicking each level).