Every time you browse the internet, DNS helps you get where you are going. Imagine if you can, having to type in something like "http://208.112.8.62" every time that you wanted to navigate to helium.com.
You probably would not spend very much time browsing. The reason you can type in a simple name or phrase to find your favorite web sites is because of DNS, or Domain Name Service.
The best way to conceptualize the service that DNS provides is to think of a directory that holds the address and phone number of every person in the world. With a single call to directory information, you could find the phone number of anyone in the world within seconds.
Every time you browse to an internet site, your computer has to find the address of that web site.
You computer asks the DNS server(s) which it is configured to contact (similar to dialing your local directory service) and asks for the internet address for the web site. If the DNS server knows the internet address, then it provides your web browser with the correct address, and your browser can now navigate successfully to the chosen web site. However, if the DNS does not have the address listed, it can either forward the request to another server for resolution or it can attempt to do the search for the address on its own. This depends on how the server is configured to handle requests for unknown addresses.
If the server is configured to look up (resolve) the address, then it breaks down the requested web site name into a first level name, a second level name, and a computer (or host) name. For a web site such as "http://www.helium.com", the first level name would correspond to the ".com" at the end of the name, the second level name would be "helium", and the host name would be, "www". The remaining "http://" portion of the web address tells your browser software that you want to talk to a world-wide web server.
Once the server has broken down the web site name into components, it sends a request to a master server, more commonly known as a "root" server. Root servers are located throughout the world and are copies of each other to ensure the highest level of availability. When contacting a root server, the DNS server provides the first level name and the second level name for which it needs an address. In turn, the root server replies with the address of the DNS server that is registered as being the "owner" of that particular address.
When your DNS server knows which other directory server holds the actual list of hostnames for a domain, it then contacts that server directly and asks for the specific address for the host name that you are looking for.
Returning to our comparison to a global phone directory, if a person in the United States wanted to make a call to a person in Darwin, Australia, the process would be as follows:
1. The American would call their local phone information number, and ask for the phone number to Jim Bigtoe in Darwin, Australia.
2. The directory services operator, not having the phone number would contact the global phone information center and ask which information center had the phone numbers for Darwin, Australia. The global information center would tell the operator which telephone center had the correct address and phone number.
3. The directory services operator would then contact the Australian phone information center in charge of Darwin, and ask them for the phone number of Jim Bigtoe. If the Australian center had the phone number registered, they would then provide it to the directory services operator.
4. The directory services operator will then tell the original requester the phone number, if it is available, or will let them know that the number is not available.\
5. The requester can then give a call directly to Joe Bigtoe.
This may seem like a long process; however, your computer can generally make these requests and get the answer back in less than 2-3 seconds.
Though address resolution is only one of the myriad of functions that DNS performs, it is also the most critical. Without DNS, the internet would probably not have grown into the information superhighway that has hundreds of millions of users on a daily basis. So the next time you browse for a web site, think about all the different processes that your one 'click' sets into motion.