Reverse domain names
DNS (Domain Name System) is a mechanism designed to search a host's domain name for its IP address and vice versa, as well as other information that resource records contain. For more information please refer to the article Resource records.
A PTR record of the reverse domain zone is used to define a domain name by IP address. Some Internet services require that IP addresses must be converted into names. To execute the request, the node address is converted to the reverse form. The translation method depends on the IP version.
IPv6 address is written as eight hexadecimal numbers from 0 to ffff separated by colons, for example, 3107:0c38:0a67:0000:0000:0000:e446:3925:0091. The domain "ip6.arpa." is used to look up domain names by IPv6 address. The IP address is written in reverse order in the domain name. For example, the address 3107:0c38:0a67:0000:0000:0000:e446:3925:0091 corresponds to the domain name "184.108.40.206.0.5.2.9.220.127.116.11.4.e.0.0.0.0.0.0.0.0.0.0.0.0.0.0.7.6.a.0.8.3.c.0.7.0.1.3.ip6.arpa.".