Domain Names
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 The Web is a collection of files that reside on computers called Web servers. These servers are located all over the world and share a connection with each other through the Internet.

Not every file on a Web server is available to the public. The owners of the Web servers decide which files should be made available.

When you are connected to the Internet, your computer is a Web client in a worldwide client/server network. A Web browser is the software application that you use to access the Web through your client machine.

Web pages are ordinary text files. They can be created in a simple text editor such as Notepad. Web pages are created using a language called HTML (Hypertext Markup Language) Tags are placed before and after the Web page's text to indicate what importance the text has relative to the rest of the document as well as how that piece of text should be displayed.

The real power of HTML comes from the anchor tag <a></a> The anchor tag allows you to create hyperlinks.

<a href="http://www.yahoo.com">Visit Yahoo</a> When the following line of HTML is viewed through a Web browser, 'Visit Yahoo' will be blue and underlined. Clicking the text will load Yahoo's home page.

You can also create links to movies, images, word documents, Adobe Acrobat files, etc.

When you run your mouse over a link, the cursor changes to a hand.

Sometimes links don't work. If you get an error that the server is busy, this may mean that too many people are trying to access pages from the server. You should try again later.  If you get an error that the DNS entry is not found this could mean that the site no longer exists. "File not found" is an error message when you type in the address of a URL wrong or the page has been moved or taken off the server.

A Web page is an individual page on a Web site. The site's main page is its home page. A home page can also mean the page that loads when your browser first opens.

Every computer on the Internet has a unique identification number called an IP address

How a Domain Name is Translated to an IP Address

Background:

  • IP address is always four numbers between 0-255.
  • First number identifies geographic region
  • Second number identifies organization
  • Third number identifies network
  • Fourth number identifies computer
  • 132.34.12.45 is valid
  1. You type Web address into browser or click on a link.
  2. Your ISP or Web server will check its cache storage to see if it has the IP address stored locally. IP address will be stored locally if someone on the network has accessed that site in the last few days. If so, ISP or Web server grabs page by connecting via IP address and sends page to user.
  3. If not, ISP or Web server connects to one of 13 root servers. The root server tells ISP/WS the IP address of top level domain server. So, if you're trying to find yahoo.com, the root server will point your ISP/WS to the .com root server. If you're trying to reach Whitehouse.gov, the root server will point you to the .gov root server.
  4. Once there, the .com server looks up the IP address for the network, in this case the Yahoo network.
  5. Once you connect to Yahoo's network, Yahoo provides your ISP/WS with the IP address of the specific machine you're trying to reach. It could the IP address for tv.yahoo.com or it could be the IP address for movies.yahoo.com.
  6. The page is sent to your browser.

There are 4.2 billion possible addresses.

If you are having difficult understanding the above information, check out this site.

Current Top Level Domains:

  • .com
  • .edu
  • .gov
  • .mil
  • .net
  • .org
  • .name
  • .info
  • .biz

There are also two letter country domain names for most of the world's countries.

Some small countries let other citizens around the world buy their names to make money!

  • .UK United Kingdom
  • .DE Germany
  • .AU Australia
  • .TV (Tuvalu NOT Television)
  • .WS (Samoa NOT World Site)

New top level domains article.

History of the Domain Name System

The IP address/domain name each identify a particular computer on the Web, but they do not indicate where a particular file is. The path to the file is indicated after the TLD.

www.raritanval.edu/departments/CIS/full-time/Schwarz/complit/index.html

is a link to my computer literacy home page. My page is a file called index.html in a folder called complit which is in a folder called Schwarz which is in a folder called full-time which is in a folder called CSET which is in a folder called departments which is on the computer named www which is on a network called raritanval....whew...

The type of operating system running on a Web server indicates whether or not the text after the TLD is case sensitive. If the file is stored on a Windows OS, it is not case sensitive. If it is stored on a Unix server, it is.

www.raritanval.edu/departments/CIS/full-time/Schwarz/complit/

will load the same page as the link above it. When you do not list the name of an explicit file, the file called "index.html" is usually loaded.

On a unix Web server:

www.raritanval.edu/home/page/index.htm

AND

www.raritanval.edu/home/page/index.HTM

are NOT the same because Unix is case sensitive. On Windows based servers, the pages ARE the same.