Easy Subnetting, Easy Networking

Subnetting is the basic foundation of Networking. All the networks in the world is based on Subnetting. Subnetting is dividing the network into many parts for various reasons like improving network security, reducing network traffic, optimising network performance and easier troubleshooting.

Every network has a network id, valid hosts and broadcast IP. The network ID is used to denote the specific network. Valid hosts are the IP that the IP used in the network. Broadcast IP is the IP that is used for broadcasting various messages.

The subnetting is done in the following steps:

Step-1) Finding the subnet mask
As per our requirement, we use a CIDR value that is used to define the size of a network. Then using the CIDR value, we find the subnet mask. This is done by writing no of 1 equal to CIDR value and remaining 0 so that there are total 32 0’s and 1’s. Then we convert it into decimal and the obtained result is the new subnet mask.

Step-2) Finding the total number of networks
Now we find the no. of networks that can be made using the subnet mask. The no of network can be calculated using the formula 2^n, where n represents the no. of 1 in the changing octate of the subnet mask.

Step-3) Finding the total valid host in a network
We now calculate the total number of IP that can be used in the network. These are the only IP accessible to any user in the network. The no of valid host is calculated using the formula 2^n-2, where n represents the no of 0 in subnet mask.

Step-4) Finding the block size of a network
Block size, jumping value or magic number all have same meaning that is the size of the network ID that changes in each network. It is calculated by 256-changing octate in subnet mask(in decimal).

Step-5) Creating a subnetting table:
Now we make a subnetting table using the given IP and the calculations we did in Step 1-4.
The table includes Network ID, Valid IP and Broadcast IP

Example:
Subneting 192.168.0.0(/27)

Step-1) New Subnet Mask
/28 means we need to have 28 1’s and remaining 4 0’s
New Subnet mask= 11111111.11111111.11111111.11100000
New Subnet mask= 255.255.255.224

Step-2) No. of network
For no. of network, we use total no of 1’s exceeding the default subnet mask of the class in the subnet mask. Here there are 3 1’s in the subnet mask.
If you got confused on default subnet mask of a class, go to this.
No of network = 2^n = 2^3 = 8

Step-3) No. of valid host
For no. of valid host, we use the total off bit in the subnet mask. Here, there are total 5 off bits.
No of valid host = 2^n(off bit) – 2 = 2^5 -2 = 32-2 = 30

Step-4) Block size
For block size, we see the leftmost octate in the subnet mask that is not equal to 255. Here that octate is fourth octate with value of 224 
Block size = 256-224 = 32

Step-5) Subneting Table

Reference: https://www.youtube.com/watch?v=_4p9KHbbXNM