DNS is nothing but a Domain Name System, which is responsible for giving out the IP addresses for the web names. For example, the IP address for yahoo.com is 206.190.60.37. It is almost difficult to remember these numbers, whenever you want to access yahoo.com. It is better we give this job to someone else, and we can ask that someone, whenever we want to know the IP for a name. And that someone is nothing but the DNS Server. And the process in which the name is getting translated into IP is called as “Address Resolution “.
How does Address Resolution happen? – By Theory
In theory, host name will have multiple names or segments.
hostname.domain.topleveldomin
For example let us take an example of the following address:
mail.yahoo.com
Here mail is nothing but a hostname, yahoo will be the domain and .com is the top level domain.
When a query is made to find out (resolve) the IP address for mail.yahoo.com, the software interprets this name from right to left and divides this name into multiple segments. This query will be recursive in order to get the final IP address. For example, in order to resolve the IP address for mail.yahoo.com, following will be the steps in theory:
1) The local systems will be configured with the addresses of root servers.
2) The root server will be queried to find out the name server of the top level domain (where is .com name server). In this case the top level domain (TLD) is .com. The reply will be the address of the name server for the .com TLD.
3) Now the TLD name server will be queried for yahoo.com (where is yahoo.com name server). The reply from the TLD name server will be the IP address of the name server of Yahoo.
4) As the final step, the Yahoo’s name server will be queried for mail.yahoo.com (where is mail.yahoo.com). The reply to this query will be the actual IP address of mail.yahoo.com.
