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It is important to note that this is the reverse order to the usual dotted-decimal convention for writing IPv4 addresses in textual form. For example, to do a reverse lookup of the IP address 8.8.4.4 the PTR record for the domain name 4.4.8.8.in-addr.arpa would be looked up, and found to point to dns.google.
This latter function, called Reverse DNS lookup, is implemented in the major uses of the domain arpa: its subdomains in-addr.arpa for Internet Protocol version 4, and ip6.arpa for IPv6. Conceptually similar lookup and mapping functionality is provided by other subdomains of arpa for specific types of data.
For reverse lookup the IETF reserved the domain ip6.arpa, where the name space is hierarchically divided by the 1-digit hexadecimal representation of nibble units (4 bits) of the IPv6 address. As in IPv4, each host is represented in the DNS by two DNS records: an address record and a reverse mapping pointer record.
For IPv6, the reverse lookup domain is ip6.arpa. The IP address is represented as a name in reverse-ordered octet representation for IPv4, and reverse-ordered nibble representation for IPv6. When performing a reverse lookup, the DNS client converts the address into these formats before querying the name for a PTR record following the delegation ...
Reverse DNS queries are used to map IP addresses to domain names. They are PTR queries for subdomains of in-addr.arpa (for IPv4 addresses) [3] and ip6.arpa (for IPv6 addresses). [4] For example, to find the domain name associated with the IP address 203.0.113.22, one would send a PTR query for 22.133.0.203.in-addr.arpa.
Reverse domain name notation (or reverse-DNS) is a naming convention for components, packages, types or file names used by a programming language, system or framework. Reverse-DNS strings are based on registered domain names, with the order of the components reversed for grouping purposes.
Link-local addresses may be assigned manually by an administrator or by automatic operating system procedures. In Internet Protocol (IP) networks, they are assigned most often using stateless address autoconfiguration, a process that often uses a stochastic process to select the value of link-local addresses, assigning a pseudo-random address that is different for each session.
A wildcard mask is a mask of bits that indicates which parts of an IP address are available for examination. In the Cisco IOS, [1] they are used in several places, for example: