IP Addressing



  • IPv4 stands for (Internet protocol version 4)
  • IPv4 uses 32 binary bits to create a single unique address on the network. An IPv4 address is expressed by four numbers separated by dots. Each number is the decimal (base-10) representation for an eight-digit binary (base-2) number, also called an octet. For example:

IP Classes

IPv4 address has been divided into five types of classes.

  • Class A
  • Class B
  • Class C
  • Class D
  • Class E

Why IPv4 divided as Classes?

The network address divided into 3 “classes”  1. Class-A large, 2. Class-B medium, and 3. Class-C small networks.
The fourth class and fifth class were essentially for “future use.“

*In Future we will discuss about the Subnetting concepts, then we might be came to know why the IPv4 Address has been divided into classes.

IP Address – Class Range

As discussed above the Internet community originally defined five address classes to accommodate networks of varying sizes. TCP/IP supports class A, B, and C addresses assigned to hosts. The class of address defines which bits are used for the network ID and which bits are used for the host ID. It also defines the possible number of networks and the number of hosts per network.

Class1st Octet Decimal Range1st Octet High Order BitsNetwork/Host ID (N=Network, H=Host)Default Subnet MaskNumber of NetworksHosts per Network (Usable Addresses)
A1 – 126*0N.H.H.H255.0.0.0126 (27 – 2)16,777,214 (224 – 2)
B128 – 19110N.N.H.H255.255.0.016,382 (214 – 2)65,534 (216 – 2)
C192 – 223110N.N.N.H255.255.255.02,097,150 (221 – 2)254 (28 – 2)
D224 – 2391110Reserved for Multicasting and using in IPv6
E240 – 2541111Experimental- used for research

Private IP Address:

A private IP address is used only in Local Area Network(LAN).


ClassPrivate NetworksSubnet MaskAddress Range
A10.0.0.0255. –
B172.16.0.0 – –
C192.168.0.0255.255.0.0192.168.0.0 –

Loopback address:

A loopback address is a type of IP address that is used to test the communication or transportation medium on a local network card and/or for testing network applications. Data packets sent on a loopback address are re-routed back to the originating node without any alteration or modification

  • The Class A addresses to is called loopback address and which we cannot be used in our network.Those IP’s are  reserved for loopback and diagnostic functions.
  • Loopback Interface is User For Device identification —  such as Systems, Firewall, Router, etc.

Difference between public and private IPv4 address


Public IP AddressPrivate IP Address
Using in WAN(wide area network)Using in LAN(Local area network)
Example: We can access the website: www.doubtsclear.com in world wide, public ip: Used for office as a unique ID for a single PC , IP: (Assigned to Systems)

IP Addressing

Why IPv4 divided in public and private IP address?

Now a days the single person is using many devices like Laptop,Mobile,Tab etc.. so we cannot provide three unique IP address for accessing those device for a single user, instead to avoid that we have concept called private IP.

  • Globally we have only 4,294,967,296 IPv4 public address

Private IPv4 reduce the consuming of public ipv4 address with the help of Network Address Translation (NAT) concept. Will see the NAT concept soon here.


  1. Information is very good and additionally Loop back- basically it is used to check the physical medium called Nic card.

  2. is anyIp and it is not possible to assign any Layer-1 devices

  3. please explain the class B subnet mask?

    • Actually Class B starts from 128 to 192. In that the private network starts from – We cannot use these private network IP’s while creating a network because these can be assigned only for a private networks like home or private sectors. The other IP’s from 128 – 192 can be assigned to medium scale industries or organizations. The default subnet mask for class B is

  4. Hi Ranjith,

    Can you please tell what you want me to explain..?

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