IP Subnetting

                                     IP SUBNETTING

General way of sub-netting:

In this way we will be using two different formulas for calculating sub-networks and Hosts.

Calculating Subnets:

Example 1:

IP: 172.16.0.1/18

                                           X.X.11000000.00000000

Formula for calculating subnetworks is 2^n  (2 to the power of n).

n = The number of bits used for Networks.

Note: as the first two octets 8+8 = 16 bits have been filled completely we should not consider them. The remaining two bits only we should consider for calculating subnetworks.

Hence,  n= 2.

Number of subnets is = 2^2 = 4

4 subnets.

They are:

172.16.0.0/18      -  172.16.63.0/18

172.16.0.64/18    -  172.16.127.0/18

172.16.0.128/18  -  172.16.191.0/18

172.16.192.0/18  -  172.16.255.0/18

Example 2:

IP: 192.168.1.1/28

The bit representation:       X.X.X.11110000  
As the first 3 octets were filled, we shouldn't consider them.
The number bits filled are : 4

Hence, for calculating number of subnets ; formula is 2^n
n=4.

2^4=16
Hence, we will get 16 subnets per network.
They are:
192.168.1.0-192.168.1.15
192.168.16.0-192.168.31.0
192.168.32.0-192.168.47.0
.. etc.

FINDING HOSTS:

Note: With this method you will get Number of Usable hosts directly.

To find the Number of hosts per subnet we should use the formula 2^n-2.

where n is number of bits filled in hosts bits.

Example 1:

IP: 172.16.0.1/18

Bit representation:  X.X.11000000.00000000

The number of bits used for networks is 18 bits. The remaining 14 bits or used for hosts.

Hence to find the number of hosts:2^n-2; 

That is: 2^14-2

The number of hosts per subnet will be: 16382.

Example 2:

IP: 192.168.1.1/29

The Bit Representation is : X.X.X.11111000

Number of Network bits: 29

Number of Hosts bits: 3

Hence to find the number of hosts 2^n-2;

n=3.

2^3-2= 6

If you have any queries regarding this topic, 

Email: poodari.sampathkumar@gmail.com