Q. Illustrate Domain Names and Address Resolution?

But what if you don't know IP address of the computer you want to connect to? What happens if you need to access a web server referred to as www.anothercomputer.com? How does your web browser know where on the Internet this computer lives? Answer to all these questions is the Domain Name Service or DNS. DNS is a distributed database, which keeps track of computer's names and their corresponding IP addresses on Internet.

Many computers connected to Internet host part of DNS database and software which allows others to access it.These computers are termed as DNS servers. No DNS server comprise the entire database; they only comprise subset of it. If a DNS server doesn't contain the domain name requested by another computer, DNS server re-directs the requesting computer to another DNS server.

Domain Name Service is structured like a hierarchy similar to IP routing hierarchy. Computer requesting a nameresolution would be re-directed 'up' the hierarchy until a DNS server is found that can resolve the domain name in the request. Figure explains a portion of the hierarchy. At the top of tree are the domain roots. Some of the older, more common domains are seen near the top. What isn't shown are multitude of DNS servers around the world which form rest of the hierarchy.

When an Internet connection is setup (for example For a LAN or Dial-Up Networking in Windows), one primary and one or more secondary DNS servers are generally specified as part of the installation. This way, any Internet applications which need domain name resolution will be able to function correctly. For illustration, when you enter a web address into your web browser, browser first connects to your primary DNS server. After obtaining IP address for domain name you entered, browser then connects to target computer and requests web page you wanted.