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Domain Name Service (DNS)

What is a Domain Name?

A domain name is a unique string that identifies a networking device which is connected to the Internet. It enables you to have an easy to recognize address for your website and your E-Mail. For example, mycompany.com.

Sub-layers of Domains

The first level domain, also known as top level domain (TLD) in the above address is ".com". This may include generic top level domains (gTLD) such as '.com', '.net','.org' or country code top level domains (ccTLD), like .lk

.lk indicates Sri Lanka, .ca indicates Canada, .de indicates Germany, .nz indicates New Zealand and so on.

Second level domain may contain the name of the organization for which the domain is registered.

The second level domain is "mycompany" in the above example.

Depending on the organization structure, the domain name may contain several subdomain names according to the user requirement. For example, you may choose,

  • mkt.mycompany.com for Marketing Dept
  • adm.mycompany.com for Administration Dept
  • eng.mycompany.com for Engineering Dept
What is DNS ?

Each and every host that runs TCP/IP within a public domain like internet must have an IP address to communicate with other devices in the network. Computers operate easily with IP addresses, but people do not. To facilitate effective and efficient communication, users need to be able to refer to networking devices by name, and still have their devices use IP addresses transparently. Domain Name System (DNS) is the process that translates friendly domain names to numeric Internet Protocol (IP) addresses.

DNS name structure

DNS names are constructed hierarchically. The highest level of the hierarchy is the last component or label of the DNS address. Labels can be up to 63 characters long and are case insensitive. A maximum length of 255 characters is allowed. Labels must start with a letter and can only consist of letters, digits and hyphens.

DNS addresses can be relative or fully qualified. A fully qualified address includes all the labels and is globally unique. A relative address can be converted by appending the local domain information. For example sunc.scit.wlv.ac.uk is a fully qualified name for the host sunc in the domain scit.wlv.ac.uk. There should strictly be a stop at the end of a fully qualified name but this is often overlooked.

The DNS was originally introduced in the United States of America and the final component of an address was generally intended to indicate the type of organization hosting the computer. Some of the three letter final labels (edu, gov, mil) are still only used by organizations based in the USA, while others can be used anywhere in the world.

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