Domain Name System.

• DNS stands for Domain Name System. When you search for a domain name in a browser, it sends a query over the internet to match the domain with its corresponding IP. 
• Once located, it uses the IP to retrieve the website’s content. Most impressively, this whole process takes just milliseconds.
• DNS is a directory service that provides a mapping between the name of a host on the network and its numerical address.
• DNS is required for the functioning of the internet.
• Each node in a tree has a domain name, and a full domain name is a sequence of symbols specified by dots.
• DNS is a service that translates the domain name into IP addresses. This allows the users of networks to utilize user-friendly names when looking for other hosts instead of remembering the IP addresses.

For example, suppose a www site at EduSoft had an IP address of 132.147.165.50, most people would reach this site by specifying www.EduSoft.com. Therefore, the domain name is more reliable than IP address.

Generic Domains

• It defines the registered hosts in the network according to their generic behavior.
• Each node in the above given tree defines the domain name, which is an index of the DNS database.
• It uses three-character labels, and these labels describe the organization type.

Country Domain

• The format of country domain is same as a generic domain, but it uses two-character country abbreviations (e.g., uk for the United Kingdom) in place of three character organizational abbreviations.

Inverse Domain

• The inverse domain is used to map an address to a name. When the server has received a request from the client, and the server contains the files of only authorized clients. 
• To determine whether the client is on the authorized list or not, it sends a query to the DNS server and ask for mapping an address to the name.

Domain Name Space

• The domain name space refers a hierarchy in the internet naming structure. 
• This hierarchy has multiple levels (from 0 to 127), with a root at the top. 
• The following diagrams shows the domain name space hierarchy.

How does DNS work?

• The process of DNS resolution involves converting a hostname (such as www.example.com) into a computer-friendly IP address (such as 192.168.1.1). 
• An IP address is given to each device on the Internet, and that particular address is necessary to find the appropriate Internet device - like a street address is used to find a particular home. 
• When a user wants to load any web-page, a translation must occur between what a user types into their web browser (example.com) and the machine-friendly address necessary to locate the example.com web-page.
• DNS is a client/server network communication protocol.