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How DNS resolves host names

DNS uses certain records for resolving a domain name to an IP address. To determine a host name based on the IP address, DNS uses the reverse lookup.

For resolving IPv4 addresses, DNS uses the A record. The A record can store a 32-bit address and can resolve IPv4 addresses. To resolve IPv6 addresses, DNS uses the AAAA record. The AAAA record can store a 128-bit address and can resolve IPv6 addresses.

IPv4 reverse DNS lookups use the in-addr.arpa domain. An IPv4 address is represented in the in-addr.arpa domain by a sequence of bytes, represented as decimal numbers, in reverse order. The numbers are separated by dots and end with the suffix .in-addr.arpa.

IPv6 reverse DNS lookups use the ip6.arpa domain. An IPv6 address is represented as a name in the ip6.arpa domain by a sequence of nibbles, represented as hexadecimal digits, in reverse order. These nibbles are separated by dots and end with the suffix .ip6.arpa.

The following table shows sample IPv4 and IPv6 addresses and their reverse DNS lookups:

IP address Reverse lookup domain name
192.0.2.10 10.2.0.192.in-addr.arpa
2001:0db8:85a3:0:0:8a2e:0370:99 9.9.0.0.0.7.3.0.e.2.a.8.0.0.0.0.0.0.0.0.3.a.5.8.8.b.d.0.1.0.0.2.ip6.arpa