Why Classless addressing prefer over classful addressing? what reason behind them?

Classless or CIDR Addressing

Why Classful addressing not used every where?

In Classful addressing millions of IP Address wasted

Class A has 16 million IP addresses

Class B has 65,000 IP addresses

Class C has 256 IP addresses.

Ex supposes a organization needed 512 IP address.

Then we see class c have only 2⁸ IP address i.e. 256 total IP address. If we use class B for addressing total IP address in class B is 2¹⁶ i.e. 65536. if we used class B 65024 IP address wasted. doesn’t make sense.

Why Classless addressing prefer over classful addressing? what reason behind them?

Classful addressing not efficient for IP address utilization so introduce classless addressing

CIDR used for efficient IP Address allocation and routing.

By allowing the distribution of IP address blocks of varying sizes, CIDR enhances the use of address space. Inefficient address allocation and IP address exhaustion are resolved by CIDR.
CIDR address is define using prefix slash ‘/’ notation.

eg.

192.143.232.21/23

here 23 define network portion of IP address it means first 23 bit is network bit and rest 9 bit is for host portion.

then subnet mask of this IP address will be

11111111.11111111.11111110.00000000=255.255.254.0

here 23 bit reserve for network portion represent by 1′ one

and rest 9 bit reserve for Host portion represent by 0′ zero.

Here some advantage of classless addressing over classful addressing.

1. maximize or Efficient use of IP addressing: – we use prefix notation rather than class, so prevent the wastage of IP Address using classful addressing.
2. Simplify the complex network requirement using CIDR Addressing.
3. Better Network performance using CIDR by efficient or better routing.

Some Key difference between both addressing Classful v/s Classless

Classful addressing	Classless addressing
VLSM(Variable length subnet masking) Not Support Support FLSM(Fixed length Subnet masking)	VLSM(Variable length subnet masking) Support
In Classful addressing IP address split into Network, Subnet and Host part.	In Classless addressing IP Address split into subnet and Host part only.
CIDR not Supported	CIDR supported
Error or Fault easily detected	compare to detect harder than classful addressing
IP address utilization is not efficient, IP address is wasted.	IP Address Utilization is efficient no wastage.

MCQ-IP Addressing-CLASSLESS CIDR OR VLSM IP Addressing – ExamHope