Calculating Total Number of Subnets Per Class

For our real life communication, we generally use Class A or Class B or Class C addresses. And the ISPs or the network engineers are always working on these classes of IP addresses. In the tutorial Classes of IP Address, we already discussed that Class D and Class E addresses are not generally used and they are used for Multicast and experimental /research.

In the following table a summarized scenario is represented where you will see the network part and host part of Class A, Class B and Class C IP addresses. Net means the Network part of that class IP address and H means the Host bit of that Class IP addresses.

Class	Total Number of Subnets Per Class	Subnets
Class A	01111111.00000000.00000000.00000000	Net.H.H.H
Class B	10111111.11111111.00000000.00000000	Net.Net.H.H
Class C	11011111.11111111.11111111.00000000	Net.Net.Net.H

The red colored bits are the most significant bits of each class of IP addresses. For details, read the tutorial IP Address Classification. So, when we would like to think about the no of subnets those bits are not needed to think.

Our goal is to determine the number of subnets of each class. In the table, you will find some bits are marked by yellow color. To calculate the total number of subnets we need to think the total number of those yellow colored bits because those are the network bits of that IP addresses. So, the total number of subnets can be calculated by using the equation = ( 2^{yellow_colored_network_bits} – 2 )

Class	No of bits to count	No of Subnets
Class A	7	27 – 2 = 126
Class B	14	214 – 2 = 16,384
Class C	21	221 – 2 = 2,097,152

What is Subnet / Subnetwork?

Subnet is a subdivision of any IP address which is logical and use to divide the whole network into multiple parts.

Subnet is sometimes referred as subnetwork.

Subnet or Subnetwork allows the flow of network traffic between hosts to be segregated based on a network configuration. By organizing hosts into logical groups, subnetting can improve network security and performance.

Subnetting which is used frequently with terms is not refers to subnet. Actually this is the practice of dividing a network into multiple subnetworks. So subnetting is just the practice of dividing a network into multiple small subnets or subnetworks.