by David Hockenbroch

Created on: December 09, 2008

Aren't you glad you don't have to remember the IP address of every website you visit? You have DNS to thank for that!

Your DNS (Domain Naming System) servers are set up as a part of your network configuration. You may have entered their IP addresses manually, or they may have been assigned to your computer by a DHCP (Dynamic Host Control Protocol) server. You can see your network configuration in several ways. In this case, we'll use the command prompt, since I'll be telling you how to see some of this system at work using it a little later. Click your start button, then click "Run". In the window that appears, type "cmd" and click "OK". This will start your command prompt.

In the command prompt, type in "ipconfig /all" and press enter. You'll see a list of information about your computer's network configuration. Among that list, you'll see your internet gateway, a primary DNS server, and a secondary DNS server. The secondary DNS server is a backup used in the event that the first one could not be reached. These are the only three IP addresses your computer needs to know to find a website. They'll be used to find all other relevant information.

When you try to visit a web page, your computer will send the request with the address you entered through the gateway to the DNS server. The DNS server stores domain names and the IP addresses where they are located. When the DNS server receives the request, it checks its own information to see if it recognizes the domain name. If it does, it sends that information back to your computer. If it doesn't, that DNS server will send the request along to its DNS server, just like your computer did, and that computer will go through the same process. It will either return the domain name to the first DNS server, which will then return it to you, or it will pass the request on to another DNS server and so on.

In command prompt, you can try this process yourself. In command prompt, type "nslookup" followed by a space and then the address of a website you normally visit, and press enter. You should soon see the name and address of your DNS server, then the domain name you entered, followed by the IP address of that domain name and perhaps some aliases for that domain. This is the information that the DNS server sends back to your computer.

Once your computer has the domain's IP address, your web browser can use that information to send a request for the page directly to that IP address. That page is then sent to the browser to be rendered, all without you ever having to know a single IP address.

After this process had been completed, your computer may also store a copy of the page in your browser's cache. The browser cache is temporary storage on your computer. When the browser has a cached copy of the page, it will check to see if there is a newer version, and, if there isn't, it will load the page from your computer instead of downloading the files from the web server again. This saves time that would normally be spent downloading pages.

You system's DNS probably also has a cache, where it stores the results of recent DNS requests. When you enter the address of a page you've recently visited, your computer will check its DNS cache first, and if it still has the results there from the last time you visited that page, it can skip the DNS step entirely and request the page.

While the process used to retrieve a web page is very complex, thanks to the Domain Name System, you need to know very little of it!

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