Domain Name

It's also useful to understand the different parts of a URL, which is comprised of parts called "domains." The chief domains of a website are its host name, second-level domain, and its first-level (or top-level) domain.

Let's use the components of the That Network home page URL as an example.Host name. The That Network URL is www.thatnetwork.com. The host name is the "www", which is short for the World Wide Web. This means this web page is hosted on the World Wide Web.

Sometimes you'll see the "www" is not there and replaced with a different host name. For example, the popular search engine and website portal Yahoo! has different host names for its features. Yahoo!'s Finance section, for example, resides at http://finance.yahoo.com, and its Games section is at http://games.yahoo.com. This means these two parts of the massive Yahoo! website reside on different hosts.

Second-level domain. In our initial example (www.thatnetwork.com), the second-level domain is "thatnetwork". This is often informally referred to as a website's "domain name," although the term "second-level domain" is technically correct.

This is the part of the domain name that identifies the business, organization or other entity operating the website. It's, if you will, the "brand name" of the website. Each second-level domain, combined with the top-level domain, must be unique. That is why registering a second-level domain is required. See Registering a Domain Name for more information.

First-level (top-level) domain. The first-level domain follows the second-level domain and is designed to describe the type or location of the website. In our example, the first-level domain of www.thatnetwork.com is "com". COM, short for commercial and often referred to as "dot com," is the most-common first-level domain, and you will see it wherever you go on the Web.

Other popular first-level domains are ORG (organization), MIL (military), EDU (educational institution), and NET (network). In recent years, new first-level domains have been approved, including BIZ (business), AERO (aerospace) and TV (television). There are also two-letter first-level domains for each country. A complete nation list can be found on the Internet Assigned Numbers Authority website at http://www.definethat.com/reference/countrycodes.asp.


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Domain Name Server

In addition to protocols, communications over the Internet and by electronic mail (e-mail) are governed with Domain Name Servers (DNS). (You will also see DNS sometimes referred to as Domain Name System or Domain Name Service.)The location of a website on the Internet is determined by its Internet Protocol (IP) Address, which is also discussed in Internet Protocol & Their Functions. This is a string of integers divided into four parts by dots with each number ranging from 0 to 255. For example: 139.201.99.2.

This numeric system is how computers understand web addresses. Now imagine if we humans had to memorize or record these numbers to visit the Internet's hundreds of millions of websites. That's why we use alphabetic names for websites-such as www.thatnetwork.com-that are the equivalent of their numeric counterparts. For example, the domain name www.thatnetwork.com has its own numeric IP Address.

This is where DNS comes in. The DNS system is essentially a huge database-undergoing constant change-that's used to map domain names to IP Addresses and IP Addresses to domain names. So when you type www.thatnetwork.com in the Address Bar of your web browser, the DNS system takes this request, recognizes this domain name's numeric IP Address, and then sends the IP Address to your web browser so it will display the web page you requested.

As you can see, navigating the Web without DNS would be difficult indeed.


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