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RDAP provides structured information about domains. Besides practical command-line query tools, there are also libraries for integrating the protocol into your own programs.

Since the early days of the Internet and its division into different organizational areas, users have needed a way to obtain information about domains, the IP addresses they use, their owners, and a way of mapping them to each other. The WHOIS protocol was devised for this purpose in 1982 and introduced in RFC 812 [1]. The service can be accessed using a command-line tool of the same name, whois. The age and importance of the protocol are evident from, among other things, its very low number – 43 – in the list of standardized ports for network services [2], which can be found in the file /etc/services [3].

Thus far, this plain-text protocol has proven its value thanks to its simplicity, even if only request and response have been standardized in a fairly rough framework. The last update in RFC 3912 dates back to 2004 [4]. (See the “Regulations on WHOIS in Europe” box for details on that topic.) The search for a replacement has been underway for some time. The ideal candidate is the Registration Data Access Protocol (RDAP) [6], which is defined in more detail in RFC 9082 [7].


The idea is for RDAP to completely replace WHOIS. It provides information about a domain via the HTTP protocol. This eliminates the need to open port 43 in the firewall. RDAP was standardized back in 2015 by an Internet Engineering Task Force (IETF) working group.


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