Subnetting in Decimal (Fast Way)

Hello Ananth

Classful IP addressing is the method for subnetting that was initially used when IPv4 was initially created. This simplified subnetting since each specific range of addresses could only have a specific subnet size. So you knew that the address must have a subnet mask of and must have a subnet mask of

However, this scheme was not scalable, as many millions of addresses were wasted especially within class A subnets.

For this reason, classless subnetting was introduced. This is where the Variable Length Subnet Mask or VLSM comes in. This essentially means that the “rule” that states that class A addresses can only have a class A subnet is relaxed. You are allowed to further subnet a class A address.

This has allowed a more efficient usage of the IPv4 address space. That’s why you see class A address spaces with subnet masks other than /8. In a classless network environment, the terms Class A, Class B, and so on are now used only as a reference and not as a concept that constrains the subnet mask size.

I hope this has been helpful!