Hi Naidu,

You probably refer to how to calculate the number of hosts in a subnet.

"n" is the number of bits from right to left that are used for hosts.

Example:

192.168.1.0/25

192.168.1.x is within the class C address range, which has a 24 bit default subnet mask.

The /25 subnet mask in this case means you have 1 bit for the subnet part and 7 bits for the host part.

This means you can have 2 subnets and 2 power 7 minus 2 hosts per subnet.

2 power 7 is 128.

128-2 is 126.

In the 192.168.1.0/25 subnet you can have then 126 hosts.

In the 192.168.1.128/25 subnet you can have another 126 hosts.

Why is the minus 2?

Because in each subnet you have an address with full 0s and another address with full 1s:

In the 192.168.1.0/25 subnet you have:

192.168.1.0 - this is the subnet itself

and

192.168.1.127 - this is the subnet broadcast address

In the 192.168.1.128/25 subnet you have:

192.168.1.128 - this is the subnet itself

and

192.168.1.255 - this is the subnet broadcast address

The address with full 0s is the subnet number itself. The address with full 1s is the subnet broadcast address. By convention they are reserved and not used for hosts.

Please make a bit-by-bit representation of the mentioned addresses and you will see what I'm talking about.

Cheers:

Istvan