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DNS Resolution Process and How DNS Server Works?

May 22, 2012

DNS servers are responsible to find out an IP address requested from client side. DNS is a set of protocols built to connect computers and known as TCP/IP. DNS works as computer GPS on internet, its job is to translate user friendly URL to an IP address like http://www.a7host.com into “173.0.139.139” and retrieving it from host. When users type website address in their browsers like Mozilla, Chrome, IE etc, Application of these browsers resolve DNS into IP address and look for it, this process is called forward DNS lookup or reverse lookup.

Forward lookup is the method of getting an IP address from DNS (domain name server) and Reverse lookup is to retrieve DNS from IP addresses. The Name server services are provided by 13 DNS servers around the world. There are total 13 Root Name servers in the world which provide name server details. DNS servers are like address books and notepads that keep the maps of IP addresses. Each device connected on internet has a unique IP address to route and retrieve information. These IP addresses are similar to phone numbers but due to DNS we don’t need to remember them in numerical form.

The process of changing or getting IP from DNS name is known as DNS Resolution or hostname resolution and the working algorithm is identified by resolver.

There are many steps performed by DNS servers or user clients to retrieve data.

  1. First of all browsers or local applications check local machine for requested domain name, if it is available then it terminate its process.
  2. If the requested domain is unavailable at local machine it send it to NS server to find associated IP address.
  3. After getting a request of IP from client, NS server checks its local cache to find weather the requested IP is recently looked up or not. If it is available in local cache then it response from there.

NS are the name servers of each country and organization. Every NS has information about its domain machines and other name servers. Top level domains (.com, .edu etc) contain the information of root name servers.

  1. Name servers checks whether domain address is local or not.
  2. Once name servers get know about domain type then they strips out the TLD (top level domain) and queries for a root like .in. NS asks to other NS who is responsible for .in.
  3. Now NS strips next higher domain and ask for its IP from responsible NS. It will return an answer say a NS with Numeric IP address.
  4. Now next higher domain is also striped out and asks from respective NS. An IP will come up with respective domain name.
  5. Now the final step is here and it ask for IP address retrieved from last step to domain name and the final IP will show.
  6. NS returns result to the application.
  7. Final results are stored in local cache of NS with expiration date to avoid fresh lookup again.
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