As I mentioned in my previous post about DNS, each time you browse to a web site or follow a link, or send someone an email, the domain name system (DNS) works behind the scenes translating the name into the correct number (IP address).
How does this process work?
Well, the guts of the DNS system consists of 13 servers called “Root Servers”. Servers are simply computers connected to the Web 24/7. These 13 root servers are coordinated by ICANN and have been placed at various spots around the world in order to spread the workload and for backup purposes. More about ICANN plus at brief history of the Internet here.
So what’s so special about these root servers?
These 13 root servers contain the vital data with the IP addresses of all of the top level domain (TLD) registries. This includes both the well-known generic TLDs like .COM, .NET, .ORG, etc. as well as the 244 country registries such as .CN (China), .FR (France), .DE (Germany), and so on.
This data is vital because if it isn’t 100% correct, it might not be possible to locate a registry on the Internet. In DNS-speak the information must be unique and authentic.
How is this information used?
All across the world there are thousands of servers called “Domain Name Resolvers”. These Resolvers routinely save (cache) the information they get from users querying the root servers. The Resolvers are located with Internet Service Providers (ISPs) and other related networks, and are used for responding to users’ requests to resolve a domain name; i.e. to find the IP address corresponding to the domain name of the web site the user wants to visit.
For example, what happens when you request to visit, say, Yahoo.com?
Your request is first sent to a local domain name resolver. The resolver then splits the request into its components. It knows where to find the .com registry because it copied that bit of information from a root server earlier. It then sends the request over to the .COM registry to find the IP address of yahoo.com. The answer is then forwarded back to your computer and the website then appears in your browser. Done!
Why do we need the Domain Name Resolvers? Why don’t we use the root servers direct?
The answer is that even though the Resolvers basically contain the same information, the 13 root servers just couldn’t handle thousands of millions of requests each day! It would slow the system to snail pace.