What is Classless Addressing?

What is IP Addressing?

Before knowing about the classless addressing, let us first know about the IP address. IP address stands for Internet protocol address. It is a numeric identity of an interface. Like a postal address provides a unique identity to a house, an IP address provides a unique identity to an interface.

The IP addresses are classified into two different categories that are as follows:

• Classful addressing system
• Classless addressing system Or Classless interdomain routing (CIDR)

What is Classless Addressing?

A classless addressing system Or Classless interdomain routing (CIDR) is an improved IP addressing system. In a Classless addressing system Or Classless interdomain routing (CIDR), the block of IP addresses is assigned dynamically based on specific rules.

A classless addressing system Or Classless interdomain routing (CIDR) is represented in terms of the block. A block is a group of IP addresses.

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Classless Addressing Notation

Notation of a classless addressing system Or Classless interdomain routing (CIDR):

p.q.r.s /n

where p.q.r.s represents the IP address, and n represents the mask bits.

What is a Classful Addressing System?

The classful addressing system was first used on the internet and was invented in 1981. The classful addressing system is the Ipv4 architecture which is divided into 5 different classes that are as follows:

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

In a classful addressing system, the IP address is a binary address of 32-bit written as four 8-bit numbers separated by dots. The four numbers are called octets. An octet is a group of 8 bits. The minimum value we can show with an 8-bit binary is decimal 0, and the maximum value we can show with an 8-bit binary is decimal 255.

Rules for Classless Addressing System Block

A classless addressing system Or Classless interdomain routing (CIDR) block is created using a set of three rules that are as follows:

• Rule 1: Every classless addressing system or CIDR block will have contiguous IP addresses. All the IP addresses in one classless addressing system block will be represented using CIDR block notation.
• Rule 2: The size of the block must always be representable in the powers of 2. The size of the block is the total number of IP addresses in the block. Any classless addressing system Or Classless interdomain routing (CIDR) block size will always be in forms 21, 22, 23, 24, 25, etc.
• Rule 3: The block’s first IP address must always be divisible by the size of the block.

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Difference Between Classful and Classless Addressing Systems

The given table describes the difference between a classful and classless addressing system based on the subnet mask, detecting fault, bandwidth, etc.

Distinguish between Classful and Classless Addressing System:

Classful addressing	Classless addressing
Classful addressing does not import a subnet mask.	Classless addressing imports a subnet mask.
In classful routing, the variable-length subnet mask is not supported.	In classless routing, the variable-length subnet mask is supported.
In classful addressing, CIDR(Classless inter-domain routing) is not supported.	In classless addressing, CIDR(Classless inter-domain routing) is supported.
In classful addressing, faults can be detected easily.	In classless addressing, fault detection is a little tough.
Classful routing requires more bandwidth.	During classless routing, it requires less bandwidth.
In classful addressing, regular or periodic updates are used.	Triggered updates are used.

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