Referral Whois (RWhois) is an extension of the original Whois protocol and service. RWhois extends the concepts of Whois in a scalable, hierarchical fashion, potentially creating a system with a tree-like architecture. Queries are deterministically routed to servers based on hierarchical labels, reducing a query to the primary repository of information.
Lookups of IP address allocations are often limited to the larger Classless Inter-Domain Routing (CIDR) blocks (e.g., /24, /22, /16), because usually only the regional Internet registries (RIRs) and domain registrars run RWhois or Whois servers, although RWhois is intended to be run by even smaller local Internet registries, to provided more granular information about IP address assignment.
RWhois is intended to replace Whois, providing an organized hierarchy of referral services where one could connect to any RWhois server, request a look-up and be automatically re-directed to the correct server(s). However, while the technical functionality is in place, adoption of the RWhois standard has been weak.
RWhois services are typically communicated using the Transmission Control Protocol (TCP). Servers listen to requests on the well-known port number 4321.
Rwhois was first specified in RFC 1714 in 1994 by Network Solutions, but the specification was superseded in 1997 by RFC 2167.
The referral features of RWhois are different than the feature of a Whois server to refer responses to another server, which RWhois also implements.
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