Application Layer

Application layer based on client & server, Request reply, query response model. In which the client questions the server and the server replies to it.
DNS is an application layer address translation protocol which resolve the user friendly address to IP address.

Note:- As the size of IP address is small so, DNS takes the services of UDP fir address translation, Request and Response.

DNS is a inverted Tree Hierarchical structure which can have maximum 128 levels raising from 0-127 levels with root node at the top(0 level) and denoted by dot.
It is based on decentralization i.e the Root distribute its authority and responsibility to children nodes that is why root node is known as null node.
The children nodes identified by levels which can be maximum 63 characters.

There are two types of domain name.

Fully Qualified Domain Name(FQDN):-

The domain name read from node up to the root node.
In FQDN the domain name terminated by the root node. Where as the partially qualified domain name does not reach the root node.

Example:- google.com (.)—->FQDN. google.com————————–>PQDN

Domain & Zone:-

Domain is that part of the Tree which may be subdivided in to further domains. Hence, it is divisible part of tree.
Zone is that part of the tree which can never further divided.
The information regarding all the nodes of a zone created maintained and updated in zone file which stored in primary server and the copy of zone file stored in secondary server through zone transmitter Hence, secondary server provides redundancy and load sharing.

Note:- The secondary server can be shared between more than 2 zones and both primary & secondary server are authoritative in nature.

Types of Domain:- There are two types of domain. 1) Generic domain 2)Country domain

1) Generic domain:- It defines the behavior of nature of business of the domain and are total 14 domains.

Example:- com, mil, gov, edu etc.

2) Country domain:- These defined by two characters of the country name and defines the country in which the domain is operating

Example:- in, US, UK etc.