Reverse DNS lookup

Reverse DNS lookup is the process of finding a host name corresponding to an IP address on a computer network such as the Internet using the Domain Name System.

Reverse DNS lookup for IPv4 addresses uses the special domain in-addr.arpa. An IPv4 address is represented in the in-addr.arpa domain by a sequence of bytes in reverse order, represented as decimal numbers, separated by dots with the suffix .in-addr.arpa. For example, the reverse lookup domain name corresponding to the IPv4 address 1.2.3.4 is 4.3.2.1.in-addr.arpa.

Reverse DNS lookup for IPv6 addresses uses the special domain ip6.arpa. An IPv6 address is represented as a name in the ip6.arpa domain by a sequence of nibbles in reverse order, represented as hexadecimal digits, separated by dots with the suffix .ip6.arpa. For example, the reverse lookup domain name corresponding to the IPv6 address 4321:0:1:2:3:4:567:89ab is b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.ip6.arpa.