WHOIS
WHOIS is a simple TCP-based query/response protocol, defined in RFC 3912, for looking up who registered a domain name or IP address block. A client opens a connection to port 43 of the responsible WHOIS server, sends the name being queried, and the server replies with a block of human-readable text before closing the connection -- there's no authentication, and RFC 3912 deliberately leaves the response's structure undefined, acknowledging the protocol "lacks many of the protocol design attributes" expected of a modern IETF standard, kept this way for historic compatibility rather than reformed. Because each registry formats, labels and discloses fields differently, and redacting data for privacy rules like GDPR is inconsistent across that unstructured text, RDAP -- a newer, JSON-based, schema-consistent protocol -- is gradually replacing it as the standard way to query registration data.
By AdminKit team, Netbase JSC · Updated