Domain Name Lookup

By Joshua Erdman
Digital Foundation, inc.

You are at your computer and unfortunately you have that advertisement stuck in your head with the little kids chanting "toysrus.com" or something like that. So you decide to look it up and see what all the fuss is about.

After opening the web browser you sing the song to yourself as you type in the address. This is what makes domain name so great they are much easier to remember than a series of numbers, but that is how the Internet actually operates, all by numerical addresses, called IP addresses. What most people do not know is that when you press the enter key after typing in a domain name in your web browser, a lot is happening in that half second before the site you are trying to view is actually displayed.

The domain you typed in is absolutely useless to your computer by itself. But what your PC can do is look up the address from the domain name you gave it by using your ISPs Domain Server on the Internet. Here is what happens:

Your computer first checks its hosts file. Typically this is located in c:\windows\system32\drivers\etc/hosts for Windows and in /etc/hosts for linux. If an entry is not listed your computer continues down to step 2.
The Domain Name cache is checked to see if it has looked up this address before. You can clear this cache in Windows by typing: ipconfig /flushdns
Your computer asks one of its assigned DNS servers if it knows the address of the specified domain name.
If the ISP DNS Server does not host the domain or if the domain is not already in the DNS Server cache, the server queries the Internet Top Level Domain Servers to find out what DNS server out on the Internet controls the specified domain (known as the domain's authoritative DNS Server).
The ISP DNS Server then contacts the Authoritative DNS Server and queries for the IP address of the specified domain
Finally the ISP DNS Server caches the answer and gives your computer the correct IP address, then your computer can establish a connection to the correct web server.

This is a typical DNS Resolution Scenario, also known as a lookup. The time it takes for all this to happen is no more than 200 or 300 milliseconds. There are many more facets about domains not mentioned here. Read the article on DNS Records to learn about how the data for these records are created and stored.

You can also use nslookup to perform your own manual DNS resolutions. It is much more detailed than using the ping utility!

Article last reviewed: 11/13/2006

Created by: Digital Foundation, inc.

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