A pointer (PTR)
record translates an IP address to its domain name. IPv4 PTR records are
represented by the octets of an IP address in reverse order with the string
"in-addr.arpa." appended at the end. For example, the PTR record for the IP
address 126.96.36.199 is 188.8.131.52.in-addr.arpa.
IPv6 addresses are
reverse mapped under the domain IP6.ARPA. IPv6 reverse-maps use a sequence of
nibbles separated by dots with the suffix ".IP6.ARPA" as defined in RFC 3596.
For example, the reverse lookup domain name corresponding to the address,
4321:0:1:2:3:4:567:89ab would be