When DNS was not in existence, one had to download a Host file containing hostnames and their corresponding IP address. But with an increase in the number of hosts on the internet, the size of the host file also increased. This resulted in increased traffic on downloading this file. To solve this problem the DNS system was introduced.

Domain Name System helps to resolve the hostname to an address. It uses a hierarchical naming scheme and distributed database of IP addresses and associated names

IP Address

IP address is a unique logical address assigned to a machine over the network.

An IP address exhibits the following properties:

  • An IP address is a unique address assigned to each host present on the Internet.
  • An IP address is 32 bits 4bytes long.
  • An IP address consists of two components: network component and host component.
  • Each of the 4 bytes is represented by a number from 0 to 255, separated with dots. For example

An IP address is a 32-bit number while on other hand domain names are easy to remember names. For example, when we enter an email address we always enter a symbolic string such as

Uniform Resource Locator (URL)

Uniform Resource Locator URL refers to a web address which uniquely identifies a document over the internet.

This document can be a web page, image, audio, video or anything else present on the web.

For example, is an URL to the index.html which is stored on examtube web server under the internet_technology directory.

URL Types

There are two forms of URL as listed below:

  • Absolute URL
  • Relative URL

Absolute URL

Absolute URL is a complete address of a resource on the web. This completed address comprises of protocol used, server name, path name and file name.

For example, http:// internet_technology /index.htm. where:

  • http is the protocol.
  • is the server name.
  • index.htm is the file name.

The protocol part tells the web browser how to handle the file. Similarly, we have some other protocols also that can be used to create URL are:

  • FTP
  • Gopher
  • mailto
  • news

Relative URL

Relative URL is a partial address of a webpage. Unlike absolute URL, the protocol and server part are omitted from relative URL.

Relative URLs are used for internal links i.e. to create links to file that is part of the same website as the WebPages on which you are placing the link.

For example, to link an image on, we can use the relative URL which can take the form like /internet_technologies/internet-osi_model.jpg. Difference between Absolute and Relative URL

Difference between Absolute and Relative URL

Absolute URLRelative URL
Used to link web pages on different websitesUsed to link web pages within the same website.
Difficult to manage.Easy to Manage
Changes when the server name or directory name changesRemains same even of we change the server name or directory name.
Take time to accessComparatively faster to access.

Domain Name System Architecture

The Domain name system comprises of Domain Names, Domain Name Space, Name Server that have been described below: Domain Names Domain Name is a symbolic string associated with an IP address.

There are several domain names available; some of them are generic such as com, edu, gov, net, etc, while some country-level domain names such as au, in, za, us etc.

The following table shows the Generic Top-Level Domain names:

Domain NameMeaning
ComCommercial business
GovU.S. government agency
IntInternational entity
MilU.S. military
NetNetworking organization
OrgNon profit organization

The following table shows the Country top-level domain names:

Domain NameMeaning
usUnited States
zaSouth Africa
ukUnited Kingdom
hkHong Kong

Domain Name Space

The domain name space refers a hierarchy in the internet naming structure. This hierarchy has multiple levels from0to127, with a root at the top. The following diagram shows the domain name space hierarchy:

image 57

In the above diagram each subtree represents a domain. Each domain can be partitioned into sub domains and these can be further partitioned and so on.

Name Server

Name server contains the DNS database. This database comprises of various names and their corresponding IP addresses. Since it is not possible for a single server to maintain entire DNS database, therefore, the information is distributed among many DNS servers.

  • The hierarchy of servers is the same as the hierarchy of names.
  • The entire namespace is divided into the zones


Zone is collection of nodes subdomains under the main domain. The server maintains a database called zone file for every zone.

image 58

If the domain is not further divided into sub domains then domain and zone refers to the same thing.

The information about the nodes in the sub domain is stored in the servers at the lower levels however; theoriginal server keeps reference to these lower levels of servers.

Types of Name Servers

Following are the three categories of Name Servers that manages the entire Domain Name System:

  • Root Server
  • Primary Server
  • Secondary Server

Root Server

Root Server is the top level server which consists of the entire DNS tree. It does not contain the information about domains but delegates the authority to the other server

Primary Server

Primary Server stores a file about its zone. It has authority to create, maintain, and update the zone file.

Secondary Server

Secondary Server transfers complete information about a zone from another server which may be a primary or secondary server. The secondary server does not have the authority to create or update a zone file.

DNS Working

DNS translates the domain name into IP address automatically. Following steps will take you through the steps included in domain resolution process:

  1. When we type into the browser, it asks the local DNS Server for its IP address. Here the local DNS is at the ISP end.
  2. When the local DNS does not find the IP address of the requested domain name, it forwards the request to the root DNS server and again enquires about the IP address it.
  3. The root DNS server replies with the delegation that I do not know the IP address of but know the IP address of the DNS Server.
  4. The local DNS server then asks the com DNS Server the same question.
  5. The com DNS Server replies the same that it does not know the IP address of but knows the address of
  6. Then the local DNS asks the DNS server the same question.
  7. Then DNS server replies with the IP address of Now, the local DNS sends the IP address of to the computer that sends the request.