TCP/IP DNS Registry Database Lookup Utility (whois/nicname)
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Utilities such as nslookup and host allow an administrator to resolve a DNS domain name to an address and also view detailed information about a domains resource records. There are cases, however, where we need to know not the technical information about a domain but rather its DNS registration information. This includes details such as what organization owns the domain, when its registration expires, and who are the designated contacts who manage it.
In the early days of DNS, all domain names were centrally registered by a single authority, called the Internet Network Information Center (InterNIC or just the NIC). To allow Internet users to look up information about domains and contacts, a special server at this center was set up. A protocol was created to allow users to retrieve information from this server, called both nicname and whois. It was initially described in RFC 812 (1982) and then later, RFC 943 (1985). Over time, the name whois has become the preferred of the two, and is the one used today for the utility program that allows an administrator to look up DNS registration data. (It can also be used to look up information about IP addresses, but is used for this purpose much less commonly.)
As the Internet grew and expanded, it of course moved away from having a single centralized authority. The modern Internet has a hierarchical structure of authorities that are responsible for registering domain names in different portions of the DNS name space. In recent years, this has been further complicated by the deregulation process that allows multiple registries for the generic top-level domains such as .COM, .NET and .ORG. All of this means that more work is needed to look up domain registration information, since it is distributed across many databases on different servers.
To make it easier for administrators to find information about domains in this large distributed database, modern TCP/IP implementations generally come with an intelligent version of the whois utility. It is able to accept as input the name of a domain and automatically locate the appropriate registry in which that domains information is located. The utility is usually used as follows:
whois [-h <whois-host>] <domain>
In this syntax, <domain> represents the name about which registration information is requested. The administrator can use the -h parameter to force the program to query a particular whois server, but again, this is usually not required. Some implementations also include other options that can be used to direct queries to particular registries.
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