Subnetting is a fundamental concept in computer networking that allows us to divide a large network into smaller, more manageable subnetworks. It is an essential skill for anyone aspiring to work with network administration or gain a deeper understanding of how networks function. Although subnetting may seem intimidating at first, this essay aims to provide a simplified explanation of subnetting, making it easy for beginners to grasp.

Understanding IP Addresses

Before delving into subnetting, it’s crucial to understand IP addresses. An IP address is a unique numerical identifier assigned to every device connected to a network. It consists of two main parts: the network address and the host address. The network address identifies the network to which a device belongs, while the host address represents the specific device within that network.

Subnet Masks

A subnet mask is a 32-bit value used to determine the network and host portions of an IP address. It works in conjunction with the IP address to identify the network and host addresses accurately. The subnet mask consists of a series of ones (1s) followed by a series of zeros (0s). The ones represent the network portion, and the zeros represent the host portion.

IP Classes and Default Subnet Masks

IP addresses are categorized into different classes: A, B, C, D, and E. Each class has a default subnet mask associated with it. Here, we will focus on the most commonly used classes – A, B, and C:

Class A:

Starts with a range of to
Default subnet mask:
Allows for a large number of hosts per network.

Class B:

Starts with a range of to
Default subnet mask:
Suitable for medium-sized networks.

Class C:

Starts with a range of to
Default subnet mask:
Ideal for small networks.

Subnetting a Network

To subnet a network, we borrow bits from the host portion of the IP address and allocate them for creating subnets. The number of borrowed bits determines the number of subnets and hosts per subnet. The formula 2^n provides the number of subnets, where ‘n’ represents the number of borrowed bits.

Calculating Subnet Masks

To calculate the subnet mask for a subnetted network, we examine the number of borrowed bits. Starting from the leftmost bit of the default subnet mask, we change the corresponding bits to zeros. The resulting subnet mask will identify both the network and the subnet.

Determining Subnet and Host Addresses

Once the subnet mask is determined, we can find the subnet and host addresses within a network. The subnet address is obtained by performing a logical AND operation between the IP address and the subnet mask. The host address is derived by performing a logical AND operation between the IP address and the inverted subnet mask.


Subnetting is a powerful technique that enables efficient network management by dividing large networks into smaller subnets. By understanding IP addresses, default subnet masks, and the process of subnetting, beginners can gain a solid foundation in this important networking concept. Remember, practice and hands-on experience will help reinforce your understanding of subnetting, allowing you to design and maintain networks effectively.