network protocols handbook.pdf

49Protocols GuideTCP/IP - Application Layer ProtocolsProtocol NameWhois (and RWhois): RemoteDirectory Access ProtocolProtocol DescriptionThe whois protocol retrieves information about domain namesfrom a central registry. The whois service is provided by the organizationsthat run the Internet. Whois is often used to retrieveregistration information about an Internet domain or server. Itcan tell you who owns the domain, how their technical contactcan be reached, along with other information.The original Whois function was to be a central directory ofresources and people on ARPANET. However, it could not adequatelymeet the needs of the expanded Internet. RWhois extendsand enhances the Whois concept in a hierarchical andscaleable fashion. In accordance with this, RWhois focuses primarilyon the distribution of “network objects”, or the data representingInternet resources or people, and uses the inherentlyhierarchical nature of these network objects (domain names,Internet Protocol (IP) networks, email addresses) to more accuratelydiscover the requested information.The RWhois defines both a directory access protocol and a directoryarchitecture. As a directory service, RWhois is a distributeddatabase, where data is split across multiple servers tokeep database sizes manageable.On the Internet, two such types of data are widely used: domainnames and IP networks. Domain names are organized via alabel-dot system, reading from a more specific label to a moregeneral label left to right. IP networks are also lexically hierarchicallabels using the Classless Inter-Domain Routing (CIDR)notation but their hierarchy is not easily determined with simpletext manipulation. Instead, an IP network’s hierarchy is determinedby converting the network to binary notation and applyingsuccessively shorter bit masks.RWhois directs clients toward the appropriate authority areaby generating referrals. Referrals are pointers to other serversthat are presumed to be closer to the desired data. The clientuses this referral to contact the next server and ask the samequestion. The next server may respond with data, an error, oranother referral (or referrals). By following this chain of referrals,the client will eventually reach the server with the appropriateauthority area.Protocol StructureThe entire RWhois protocol can be defined as a series of directives,responses, queries, and results.rwhois-protocol = client-sends / server-returnsclient-sends = *(directives / rwhois-query)server-returns = *(responses / rwhois-query-result)Related protocolsTCP, SMTP, FTP, Finger, DNSSponsor SourceWhois is originally defined by IETF (http://www.ietf.org).Referencehttp://www.javvin.com/protocol/rfc954.pdfNickname/Whoishttp://www.javvin.com/protocol/rfc2167.pdfReferral Whois (RWhois) Protocol V1.5