What is Classless Addressing?

By Priyanshu Vaish|Updated : August 26th, 2022

Classless Addressing is one of the IP(Internet Protocol) address classifications. IP addresses are unique and universal. No two hosts will simultaneously have the same IP address in the world. The most common use of the classless addressing system Or Classless interdomain routing (CIDR) for actually addressing is to combine two or more class C networks to create a /23 or /22 Supernet.

For example, the class C networks 192.168.32.0 and 192.168.33.0 could be combined to create 192.168.32.0/23. Know more about classless addressing, IP addressing, classful addressing, and more detail.

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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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FAQs on Classless Addressing

  • A classless addressing system or classless interdomain routing (CIDR or supernetting) is the way to combine two or more class C networks to create a /23 or /22 Supernet. For example, the class C networks 192.168.32.0 and 192.168.33.0 could be combined to create 192.168.32.0/23.

  • A classless addressing system or Classless interdomain routing (CIDR) is an improved IP(Internet protocol) addressing system. In a Classless addressing system or Classless interdomain routing (CIDR), the block of IP addresses is assigned dynamically based on the certain rules.

  • A classless addressing system or classless interdomain routing (CIDR) was developed to alternative traditional subnetting. We can add the specification in the IP(Internet Protocol) address itself as to the number of significant bits that make up the networking portion.

  • The subnet masks serve the same purpose as CIDR(classless interdomain routing) blocks, which are formatted differently. Instead of an IP(Internet Protocol) address followed by the one- or two-digit number, it is an IP(Internet Protocol) address followed by four more numbers, each separated by the decimal point.

  • Classless addressing system or a classless interdomain routing (CIDR) notation specifies an IP address, the slash ('/') character, and decimal number. The decimal number is a count of consecutive leading 1 bit (from left to right) in the network mask. The number can also be the width (in bits) of the network prefix.

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