Reverse lookup in networking refers to the process of determining the domain name associated with a given IP address by querying the Domain Name System (DNS). This is the opposite of a forward DNS lookup, which starts with a domain name and returns its corresponding IP address.
The process uses special DNS records called Pointer (PTR) records. For IPv4 addresses, the IP address is reversed and appended to the .in-addr.arpa domain. For example, the IP address 192.0.2.1 would be queried as 1.2.0.192.in-addr.arpa. For IPv6 addresses, the process is similar but uses the .ip6.arpa domain. The DNS server is queried for a PTR record at this reversed address. If a PTR record exists, the server returns the associated domain name.