Subnetting in Decimal (Fast Way)

[lagapidis (Lazarus Agapidis)]

Hello Ajeet

@talk2ajeet911

In your second paragraph, you have mentioned that if we were to subnet 192.168.1.0/24 to subnet mask /25, then the first subnet should be 192.168.1.0. Why can’t we take the first subnet as 192.168.1.128 - This can be the network address and the broadcast address can be 192.168.1.255.

If you are originally given a range of 192.168.1.0/24, and you begin dividing it into smaller subnets, the first subnet is always the lowest. So if we begin dividing this into /28 subnets for example, the first subnet will be 192.168.1.0/28. The second will be 192.168.1.16/28, then 192.168.1.32 and so on. Of course, each subnet has its network address, first, last and broadcast addresses as well…

@talk2ajeet911

Also, I think in the first line of 3rd paragraph, it should be 192.168.2.0/26. Please correct me if I am wrong.

Actually, I meant /23. 192.168.2.0/23 gives us a range of addresses from 192.168.2.0 to 192.168.3.255.
If we subdivide this into smaller subnets using the 255.255.255.192, then we get the following subnets:

192.168.2.0/26
192.168.2.64/26
192.168.2.128/26
192.168.2.192/26
192.168.3.0/26
192.168.3.64/26
192.168.3.128/26
192.168.3.192/26

The example I used was to show that you start with an original range, and depending on the sizes of the subnets you want to make, you can divide that into smaller pieces.

I hope this has been helpful!

Laz