- An application layer protocol is responsible for defining the communication process between different applications running on different systems. It specifies the format, structure, and content of messages exchanged between these applications.
- DNS, or Domain Name System, is a critical directory service that provides a mapping between the name of a host on the network and its corresponding numerical address. The DNS system is required for the functioning of the internet as it allows users to connect to other hosts using easy-to-remember domain names instead of having to remember complex IP addresses.
- The DNS system is organized as a hierarchical tree, with each node in the tree having a domain name. A full domain name is a sequence of symbols specified by dots that uniquely identifies a host on the network. The DNS system translates domain names into IP addresses, which enables users to access other hosts using user-friendly names instead of having to remember IP addresses.
- For example, instead of having to remember that the FTP site at EduSoft has an IP address of 126.96.36.199, users can access the site by specifying ftp.EduSoft.com. This makes domain names more reliable than IP addresses for accessing hosts on the network.
- DNS is a TCP/IP protocol that is used on different platforms, and the domain name space is divided into three different sections: generic domains, country domains, and inverse domain. The generic domains represent categories of organizations, such as .com for commercial entities or .org for non-profit organizations. The country domains represent countries, such as .us for the United States or .jp for Japan. The inverse domain is used for reverse DNS lookups, which allows users to obtain the domain name associated with a particular IP address.
- The DNS system defines registered hosts based on their generic behavior.
- Each node in the DNS tree is associated with a domain name, which serves as an index to the DNS database.
- Domain names are typically constructed using three-character labels that describe the type of organization associated with the host.
|aero||Airlines and aerospace companies|
|biz||Businesses or firms|
|coop||Cooperative business Organizations|
|info||Information service providers|
|museum||Museum & other nonprofit organizations|
|net||Network Support centers|
|pro||Professional individual Organizations|
The format of a country domain is similar to that of a generic domain, but it uses two-character country abbreviations, such as “us” for the United States, instead of three-character organizational abbreviations.
The inverse domain is utilized for mapping an address to a name. In situations where a server receives a request from a client, and the server only contains files belonging to authorized clients, it needs to determine whether the client is on the authorized list or not. To do this, the server sends a query to the DNS server, requesting a mapping of the address to the name associated with the client.
Working of DNS
- DNS is a client/server network communication protocol. DNS clients send requests to servers, and DNS servers send responses to clients. Client requests typically include a hostname, which is then translated into an IP address through a process known as forward DNS lookups. Conversely, requests containing an IP address can be translated into a hostname through reverse DNS lookups.
- DNS utilizes a distributed database to store the names of all hosts available on the internet. When a client such as a web browser sends a request containing a hostname, a piece of software called a DNS resolver sends a request to a DNS server to obtain the IP address associated with the hostname.
- If the DNS server does not contain the IP address for the requested hostname, it forwards the request to another DNS server. Once the IP address is obtained by the resolver, it can then complete the request over the internet protocol.