Inverse DNS Queries (also called as Reverse DNS Queries) works just exactly opposite to normal DNS Queries. Inverse DNS Queries (Reverse DNS Queries) are used when the user wants to resolve the IP Address to a Fully Qualified Domain Name. In other words, the user has the IP address and he wants to find out the Fully Qualified Domain Name corresponding to that IP Address. For Inverse name resolution (Reverse name resolution), Pointer (PTR) records are used. Pointer (PTR) records added to the in-addr.arpa domain. PTR (Pointer) Resource Records must be added in local DNS Server for Inverse Name Resolution to work properly.
For Example: If a user wants to resolve the FQDN for the IP address 192.168.100.123, would send the local DNS Server a request for the PTR record for 188.8.131.52.in-addr.arpa.