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A Canonical Name (CNAME) record is a type of resource record in the Domain Name System (DNS) that maps one domain name (an alias) to another (the canonical name). [1]This can prove convenient when running multiple services (like an FTP server and a web server, each running on different ports) from a single IP address.
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. If the A record for dns.google in turn pointed back to 8.8.4.4 then it would be said to be forward-confirmed.
It is a successor to the WHOIS protocol, used to look up relevant registration data from such Internet resources as domain names, IP addresses, and autonomous system numbers. While WHOIS essentially retrieves free text, RDAP delivers data in a standard, machine-readable JSON format. [1]
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.
In 1993 the U.S. Department of Commerce, in conjunction with several public and private entities, created InterNIC to maintain a central database that contains all the registered domain names and the associated IP addresses in the U.S. (other countries maintain their own NICs (Network Information Centers) -- there is a link below that discusses Canada's system, for example).
Returns all records of all types known to the name server. If the name server does not have any information on the name, the request will be forwarded on. The records returned may not be complete. For example, if there is both an A and an MX for a name, but the name server has only the A record cached, only the A record will be returned.
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 domain name system acts like a large telephone directory and within is the master database, which associates a domain name such with the appropriate IP number. When the domain name is registered/purchased on a particular registrar's "name server", the DNS settings are kept on their server, and in most cases point the domain to the name ...