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Domains

Last updated Oct 17, 2003.

A domain name identifies one or more IP addresses used in the URL to locate a Web site. For example, http://www.informit.com is a domain name that can have multiple IP addresses tied to its name. In other words, it's easier to remember InformIT's domain name of http://www.informit.com than its Internet Protocol (IP) address of http://63.240.93.131/.

The last part of the domain name, .com (which means commercial), is the top-level domain name. When reading the parts—also known as labels or octets—of the domain name, the part to the right of .com is its subdomain. Informit is considered the subdomain of .com.

The first part of the domain name—www—is the hostname. The www (World Wide Web) isn't the same thing as the Internet. The Internet is a series of connections exchanging data, including email and content. The www provides the Web pages, audio, videos, animation, and graphics. The www can't do anything without the Internet's connection.

Each domain name is unique. When you enter http://www.informit.com, you know you'll get InformIT's Web site. Most state government URLs, however, look more like http://www.state.tx.us.

In this case, us is the top-level domain name, tx is the subdomain of us, and state is the subdomain of tx. The top-level domain is the broadest, encompassing of many subdomains. As you move to the right of that, the subdomains get more specific.

Many sites use a hostname name other than www such as blog.informit.com, webdesign.informit.com, and en.informit.com. [Note: These URLs are not active.]

URL's Role

Domain names, IP addresses...where does URL fall? A URL takes your browser to a specific file on a specific computer on the Internet. For example, the URL http://www.informit.com/articles takes you to InformIT's Articles page. Pick an article and the URL http://informit.com/isapi/product_id~{801D5EA5-F03C-47A8-A606-6162F4EB8AC4} appears. http://www.informit.com is the domain name that has already been identified through a domain name server. Clicking on the different links within the InformIT Web site takes you to different URLs within InformIT's domain name.

Notice that most URLs end with a few little letters such as .com, .net, .gov, .ca, or .de—just to name a few. What is it about those letters at the end of the URL? In the '90s, most top-level domain names were limited to .com, .net, .gov, .edu, and .org. In terms of the 'Net, .com refers to commercial organizations, .edu to educational institutions, .net to networking companies, .gov to government pages, and .org to organizations or nonprofits. International designations are identified with two letters, such as ca for Canada, de for Germany, co.uk for United Kingdom, and es for Spain. Over the years, the line between .com and .net has blurred as the rules have loosened and a growing list of top-level domain names have been added to the mix including .tv, .biz, .info, .cc, and .name.

For most sites, name.com is sufficient and www can be omitted to save typing. However, some sites won't work without the www and, in rare instances, might send you to a totally different site. The omission of the www depends on how the server is configured. You should ask a potential ISP whether it can handle both http://www.name.com and name.com.

Sticking IP to a DNS

So, how does the domain name get tied in with the IP address? First, you must go to a registrar's site to sign up and create a domain name. Next, you'll need to line up a server—the IP address comes from the server that's hosting the domain name. IP addresses have 32-bit numbers with four sets (also known as octets), which are separated by dots. Each octet has a value between 0 and 255. The following is InformIT's IP address:

http://63.240.93.131/

How To Find an IP Address

Of course, if you look up Informit.com, it's possible you'll see a different IP address—it's changed over the course of the years. If you're a Windows user, you can look up Informit's IP address by opening the DOS command window (Start > Run > type "cmd" without the quotes > click OK), typing "nslookup http://www.informit.com," and pressing Enter. You can find out your own computer's IP address by typing "ipconfig" in the DOS command window or you can take the easy way out and just go to http://www.whatismyip.com/. To get a PC's hostname, type "hostname."

You can also look up the IP address of a domain name by using PING. Go to the MS-DOS prompt (Start > Run > type "cmd") and type ping http://www.informit.com (or any Web site address) to see the IP address.

What is DNS?

DNS, or Domain Name System, is actually a network of computers that translates domain names into IP addresses. Each domain name is mapped to an IP address, which represents a physical location of the machine where the files live. Multiple domain names can be mapped to the same Internet address, which is how businesses, individuals, and organizations can have separate identities while sharing the same server.

Many computers contain the list of domain names and their corresponding addresses. When you enter http://www.informit.com into a browser's address box, the browser connects to the nearest DNS server to request the IP address for http://www.informit.com. If it doesn't know the answer, the request goes up to the next DNS in the hierarchy. It continues to do this until a server is found containing the required information, which sends the answer back to your browser. The DNS has a simple job, but the process to make it happen is complex.

Thanks to the DNS, we don't have to bother memorizing long and ever-changing IP addresses. IP addresses point to a server's physical location, remember? If you move your site to a new server, the IP address changes to reflect your site's new locale. What's great about domain names is that they never change, regardless of where you park your site on the 'Net.

Registering Your Domain Name

Domain names must be unique on the Internet and registered with an ICANN-accredited registrar. The Internet Corporation for Assigned Names and Numbers (ICANN) Web site has a listing of such accredited registrars. ICANN is a non-government, non-profit corporation responsible for IP address space allocation, domain name system management, parameter assignment, and root server system management functions.

To register a domain name, go to one of the accredited registrars and complete the form, which asks for owner contact information, administration contact information, billing contact information, technical contact information, and payment information. The last and most critical piece of information is the nameserver information. You are not expected to have this information on hand and can change or remove the information after completing registration.

After registering and finding a host server, the host server provides you with the 1st and 2nd nameserver information. Enter this information with the registrar—and that's it. It takes a day or two for the name server to propagate, but until then you can get to your Web site address using the IP address.