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In Network Layer of OSI Model we have discussed that the Network Layer is mainly responsible for Host-to-Host Delivery means, a device (computer or a router) to device. A computer somewhere in the world needs to communicate or correspond with another computer somewhere else in the world. Typically, a computer communicates through internet.

For this level of communication, we need a global addressing system, it is called Logical Addressing. Today, we use it as IP Address mean the the logical address in the network layer of TCP/IP Protocol Suite.

IPv4 Addresses

An IPv4 address means Internet Protocol address version 4, which is a 32-bit long address that uniquely and universally defines the correlation or the connection between a device to the internet.

In another way, if a device operating at network layer has 'm' no of connections to the internet, then it needs to have 'm' no of addresses.

Address Space

An IPv4 address defines addresses that has an address space. Since IPv4 uses 32-bit addresses, apparently it has it has an address space of 232 or 4,294,967,296 (more than 4 billions).

Which means hypothetically if, there were no restrictions more than 4 billion devices can be connected to the internet.

An IP address simply looks like

Now, if we convert it into binary it will simply looks like 11000000.10101000.00000000.00000001

So, its frequent to here an IPv4 address referred to an 4-byte address.

Types of Addressing

There are two types of addressing,
  • Classful Addressing
  • Classless Addressing

Classful Addressing

In classful addressing, the IPv4 address space is divided into five classes, such as: 

Class A, Class B, Class C, Class D, and Class E

Now if we place the classes in dotted-decimal notation, the classful addresses will look like the table below,

ip address, ip address format

Let us examine the table. When an organization requests a block of addresses it will be granted any one from class A, B or C.

Class A addresses were designed for large organizations with number of hosts or routers attached.

Class B addresses were designed for medium size organizations with tens of thousands hosts or router attached.

Class C addresses were designed for small-cap organizations with relatively small number of hosts or routers attached.


Class D addresses were designed for Multicasting

Multicasting means, when a single sender transmits one of the types of data packet to several nodes or routers across the world at the same time.

Class E addresses are reserved for future use. Only few were used resulting in another waste of addresses.

In classful addressing, IP addresses in class A, B or C are divided into two parts netid and hostid. These are varying lengths depending on the class of the address.

However, the length of the netid and hostid (means in bits) is predetermined in classful addressing which is called mask.

Default masks of classful addresses are given below:

ip address, ip to decimal


1. What is the address space in bits of IPv4 Addressing?

2. Explain why most of the addresses in class E are wasted.

3. Explain why a med-cap or large-cap companies does not want a block of Class C addresses.

4. What is the number of bytes in an IPv4 Address represented in dotted-decimal notation?

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