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There's one other DNS client application that's worthy of some discussion. Rather than being used to query DNS servers, “who is” is a tool used to query who is servers. Who is servers maintain all the domain registration information for the Internet DNS namespace. Using who is, you can see who has registered a specific domain, and see what the authoritative DNS servers for the domain are. These servers specified in the domain name registration, are used to control delegation in the DNS hierarchy. This information tells higher level DNS servers where to direct a request during the recursion process. There're two ways to use who is, on the world wide web and from the systems command line. The most common place to use who is on the web, is the network solutions web site. In your web browser go to www.networksolutions.com, and click the “who is” link in the top right corner. If you want, can also go directly to www.networksolution.com/cgi-bin/whois/whois. This is the network solution’s who is tool for most registrars, have there own who is tools. As network solutions is the largest domain registrar, its who is tool is one of the most commonly used. Most domains can be looked up through any who is server regardless of where they’re registered. To use a “who is” tool, enter the domain name tool lookup and click go. Make sure you enter just the domain and not any host names. For example, you'd enter vtc.com and not www.VTC.com. Results of the who is look up, will typically show different information based on whether or not the domain is registered through network solutions. For a domain registered with network solutions, the register information and the information for the administrative technical and building contracts will be shown, along with the expiry, and the authoritative servers. Domains not registered through network solutions will show who the registrar is, the name servers and expiry dates for the domain. Typically, you can then go to the actual registrars who is tool and find the registrant, and administrative technical and building contact information for the domain. Most versions of UNIX also include a who is tool; to use it, type whois, followed by the domain to look up. Typically, you'll get the name of the registrar, the name servers, and expiry date for the domain. This information isn't all that useful, as if the who is server querying won't give the registrant information on a domain unless it's registered with the registrar hosting the who is server. If you look at the output of the who is command though, you'll see a who is server line in response. Type the command whois -h, followed by the who is server provided in the response, followed by the domain to look up. This time you'll get the full registering information, as you're querying the proper who is server. Who is isn't that useful as a DNS tool, but it can be very useful when you want to check to ensure that the authoritative DNS servers for your domain are set correctly; if you're hosting a domain on your own DNS servers you need to ensure hat those servers are specified in the registration, make sure your DNS servers have that zone configured correctly. If both of these requirements are met, your domain should resolve properly from anywhere own the Internet. One thing to note is that any changes made to the authoritative DNS servers on a registered domain can take a day or two to propagate across all of the proper name servers.