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In computer networks, a reverse DNS lookup or reverse DNS resolution (rDNS) is the querying technique of the Domain Name System (DNS) to determine the domain name associated with an IP address – the reverse of the usual "forward" DNS lookup of an IP address from a domain name. [1]
That is, the reverse DNS might verify, but it will usually be part of another domain than the claimed domain name. Using an ISP's mail server as a relay may solve the reverse DNS problem, because the requirement is the forward and reverse lookup for the sending relay have to match, it does not have to be related to the from-field or sending ...
Reverse lookup is a procedure of using a value to retrieve a unique key in an associative array. [1] Applications of reverse lookup include reverse DNS lookup, which provides the domain name associated with a particular IP address, [2] reverse telephone directory, which provides the name of the entity associated with a particular telephone ...
The domain name arpa is a top-level domain (TLD) in the Domain Name System (DNS) of the Internet. It is used predominantly for the management of technical network infrastructure. Prominent among such functions are the subdomains in-addr.arpa and ip6.arpa, which provide namespaces for reverse DNS lookup of IPv4 and IPv6 addresses, respectively.
These servers are registered in the DNS directory as the authoritative servers for the reverse lookup zone of the 10.0.0.0 / 8, 172.16.0.0 / 12 and 192.168.0.0 / 16 addresses. These servers are configured to answer any query with a "nonexistent address" answer.
A reverse DNS lookup is a query of the DNS for domain names when the IP address is known. Multiple domain names may be associated with an IP address. The DNS stores IP addresses in the form of domain names as specially formatted names in pointer (PTR) records within the infrastructure top-level domain arpa. For IPv4, the domain is in-addr.arpa.
nslookup operates in interactive or non-interactive mode. When used interactively by invoking it without arguments or when the first argument is - (minus sign) and the second argument is a hostname or Internet address of a name server, the user issues parameter configurations or requests when presented with the nslookup prompt (>).
The PTR DNS records in the reverse DNS can be used for a number of things, including: Most email mail transfer agents (mail servers) use a forward-confirmed reverse DNS (FCrDNS) verification and if there is a valid domain name, put it into the "Received:" trace header field.