Whois

Whois is a TCP-based query/response protocol which is widely used for querying a database in order to determine the owner of a domain name, an IP address, or an autonomous system number on the Internet. Whois lookups were traditionally made using a command line interface, but a number of simplified web-based tools now exist for looking up domain ownership details from different databases. Web-based whois clients still rely on the whois protocol to connect to a whois server and do lookups, and command-line whois clients are still quite widely used by system administrators.

The whois system originated as a method that system administrators could use to look up information to contact other IP address or domain name administrators (almost like a "white pages"). The use of the data that is returned from query responses has evolved from those origins into a variety of both altruistic (such as a Certificate Authority validating the registration for ecommerce https) and nefarious uses (such as bulk unsolicited email campaigns).

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