Domain Name System

Each device connected to the public internet has a unique numeric address called IP address. An IP address is like a phone number which is difficult to remember. To simplify the identification of device on internet, the DNS was invented. Domain Name System translates IP address to alphanumeric names known as domain name. The domain name is human readable form of IP address.  For example, IP address google.com is 173.194.36.65. Thus it is easy to remember google.com then its IP address 173.194.36.65.

Namespace

A namespace is a grouping in which names can be used to symbolically represent another type of information, such as an IP address, and in which specific rules are established that determine how names can be created and used

Internet before DNS

Before the implementation of DNS, the use of names to locate resources on TCP/IP networks was supported by a file called Hosts. Network administrators entered names and IP addresses into Hosts, and computers used the file for name resolution.

Hosts file posed a problem for network administrators. As the number of computers and users on the Internet grew, the task of updating and distributing the Hosts file became unmanageable. Thus DNS was introduces to rescue the internet.

Domain Name System

Domain Name System (DNS) is a distributed database that implements a hierarchical naming system. DNS is based on hierarchical and logical tree structure known as domain namespace. A domain namespace consists of tree structure of domain names with root domain at the top. Immediately below the root, there are major domains such as .in, .net, .com, .org etc. From these domains, the name space can branch into multiple paths, with each intersection point called a node and labeled with a simple name.

Each node in DNS tree represents a DNS name. a DNS name can be DNS domains, computers and services.

For example, refer to the below DNS tree. Here google.com is a DNS domain. The domain google.com is further divided to create sub-domain mail.google.com.

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Every node in the DNS domain tree can be identified by a fully qualified domain name (FQDN). An FQDN is a domain name that contains the full name of a host. It contains all labels, from the most specific to the most general, that uniquely define the name of the host. For example, the FQDN for the news server in the yahoo.com DNS domain is constructed as news.reskit.com. The dot is a standard separator between two labels in the tree.

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Common Top Level Domains (TLD)

Here are some of the common top level domains used widely over the internet.

Domain name Purpose
.com com refers to commercial. The most popular TLD, .com was meant to be used for commercial purposes.
.net net refers to network. This was Intended for network web sites
.org org refers to organization. It was originallyintended for sites that represent organizations and non-profits.
.edu edu refers to education. This is usually used by colleges and other educational institutions, and it is not typically available for public registration.
.mil mil refers to military. It is restricted to military use only. It is not available for public registration.
.gov gov refers to government. It is restricted to government use only. It is not available for public registration.
.co co refers to company. It was meant as alternative to .com.
.biz biz refers to business. It is intended for business use, but its popularity fades in comparison to the .com.
.info info refers to informational.
.me me refers to personal. It is often used for personal websites.
.in in referes to India. It is often used by entities operating in India to target Indian customers.


Internet Corporation for Assigned Names and Numbers (ICANN)
is responsible for managing domain names. It is responsible for management of root name servers.

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