on sites such as sourceforge.net. However, most modern WHOIS tools implement command line flags or options, such as the -h option to access a specific server host, but default servers are preconfigured. Additional options may allow control of the port number to connect on, displaying additional debugging data, or changing recursion/referral behavior. Like most TCP/IP client–server applications, a WHOIS client takes the user input and then opens an Internet socket to its destination server. The WHOIS protocol manages the transmission of the query and reception of results. Web With the advent of the World Wide Web and especially the loosening up of the Network Solutions monopoly, looking up WHOIS information via the web has become quite common. At present, popular web-based WHOIS-queries may be conducted from ARIN, RIPE and APNIC. Most early web-based WHOIS clients were merely front-ends to a command-line client, where the resulting output just gets displayed on a web page with little, if any, clean-up or formatting. Currently, web based WHOIS clients usually perform the WHOIS queries directly and then format the results for display. Many such clients are proprietary, authored by domain name registrars. The need for web-based clients came from the fact that command-line WHOIS clients largely existed only in the Unix and large computing worlds. Microsoft Windows and Macintosh computers had no WHOIS clients installed by default, so registrars had to find a way to provide access to WHOIS data for potential customers. Many end-users still rely on such clients, even though command line and graphical clients exist now for most home PC platforms. Microsoft provides the Sysinternals Suite that includes a whois client at no cost. CPAN has several Perl modules available that work with WHOIS servers. Many of them are not current and do not fully function with the current (2005) WHOIS server infrastructure. However, there is still much useful functionality to derive including looking up AS numbers and registrant contacts. Servers WHOIS services are mainly run by registrars and registries; for example the Public Interest Registry (PIR) maintains the .ORG registry and associated WHOIS service. Regional Internet registries WHOIS servers operated by regional Internet registries (RIR) can be queried directly to determine the Internet service provider responsible for a particular resource. The records of each of these registries are cross-referenced, so that a query to ARIN for a record which belongs to RIPE will return a placeholder pointing to the RIPE