Understanding the Domain Name System
Computers on the Internet communicate using unique strings of numbers called IP (Internet Protocol) addresses like 22.214.171.124 to locate each other or other resources on the internet. The use of IP addresses posed a difficult situation for people to remember those strings of numbers; therefore in 1983 the Domain Name System (DNS) was introduced.
The Domain Name System (DNS) is a distributed database that translates domain names like google.com into IP addresses such as 126.96.36.199. The use of domain names like google.com now makes it possible for people to locate a website or other Internet resources using a human readable and memorable format instead of typing in a string of numerical addresses like 188.8.131.52. A domain name is therefore a human readable and memorable representation of an IP address.
Structure of the Domain Name System
At the highest level of the domain name system is the Root zone which is nameless. This root zone is managed by Internet Corporation for Assigned Names and Numbers (ICANN) through the Internet Assigned Numbers Authority(IANA) function and is maintained by Verisign. Below the root zone comes the Top Level Domains (TLDs) i.e .com, .org, .net e.t.c. These Top Level domains are managed by different registries.
The DNS processes domain names following their hierarchical structure. A domain name is composed of different parts separated by “dots” and each part represents a hierarchy in the domain name structure and this hierarchy descent from the right to the left part of the domain name. The different parts that make up a domain name are called labels. The furthest right or the rightmost label is known as the Top Level Domain. In example.com “.com” is the Top Level Domain (TLD), “example” is the Second Level Domain (SLD) and in training.example.com, “training” is the third level domain.