Extended-Network-Prefix

For enhancing subnetting Extended-Network-Prefix is introduced, where to the default subnet mask (class A - 255.0.0.0, Class B - 255.255.0.0, Class C - 255.255.255.0) some more 1bits is used further contiguous 1bits and the length of network address increase. This idea is to divide the standard classful host-number field into two parts - the subnet-number and the host number on that subnet. It is three level hierarchy instead of two level hierarchy.

To calculate the number of subnets or hosts, use the formula (2^n-2) where n = number of bits in either field, and 2^n represents 2 raised to the nth power. Multiplying the number of subnets by the number of hosts available per subnet gives you the total number of nodes available for your class and subnet mask. For example read the post Subnet Design.