Here's how reverse IP lookup typically works:

Querying the DNS Database: The reverse IP lookup tool or service queries the DNS database, specifically the PTR (Pointer) records, which store the reverse mapping of IP addresses to domain names.

The DNS database contains these records when they have been properly configured by the domain owner or the hosting provider.

Retrieving Domain Names: If a PTR record exists for the IP address, the reverse IP lookup tool retrieves the associated domain name(s).

This could be a single domain name or multiple domain names, depending on the hosting configuration.

see also

Reverse IP lookup