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Subnetting in Computer Networks

Last Updated on April 13, 2023 by Prepbytes

Subnetting in computer networks is an important technique that allows network administrators to divide a larger network into smaller subnetworks. This helps in better management and efficient utilization of network resources. This article discusses subnetting in computer networks, how subnetting in computer networks works, examples of subnetting, advantages, and disadvantages of subnetting in computer networks. So, without any further delay, let’s move on to our next section.

What is Subnetting in Computer Networks?

Subnetting in computer networks is a technique that allows a single network to be divided into multiple smaller networks, known as subnets.

Think of it like dividing a large city into smaller neighborhoods, each with its own unique address range. This makes it easier for devices to communicate within their own neighborhood without the need to send messages to every device in the city.

Subnetting involves creating a logical separation of a network by extending the subnet mask beyond its default value. This allows for more subnets to be created and a limited number of hosts to be allocated within each subnet.

By doing this, the network administrator can allocate specific IP address ranges to each subnet, making it easier to manage and troubleshoot network issues. This also improves security by isolating traffic between subnets and reducing the risk of unauthorized access.

Overall, subnetting in computer networks is a technique used to better organize, allocate resources, and improve security.

How does Subnetting in Computer Networks Work?

Subnetting, as we now know, divides a network into small subnets. Routers are used to communicate between subnets, and each subnet allows its connected devices to communicate with one another. The size of a subnet is decided by the network technology used and the number of connections required. Each organization is responsible for determining the number and size of subnets it generates within the constraints of the address space available for its use.

Let’s look at how subnetting divides a network into subnets.

An IP address is made up of two fields: a Network Prefix (also known as the Network ID) and a Host ID. The way the Network Prefix and the Host ID are separated depends on whether the address belongs to Class A, B, or C. The picture shown below illustrates an IPv4 Class B address with a value of The first two octets (172.16) represent the network prefix, while the last two octets (37.5) represent the host ID.

To generate subnets, we commonly fix the MSB (Most Significant Bit) bits of the Host ID. The image below illustrates how we can create two network subnets by fixing one of the host’s Most Significant Bit (MSB) bits. We cannot modify network bits because doing so changes the entire network.

A subnet mask is needed to identify a subnet, which is calculated by substituting ‘1’ for all Network ID bits and the number of bits reserved in Host ID to generate the subnet. The subnet mask is responsible for routing data packets from the internet to the desired subnet network. A subnet mask also determines which part of an address will be used as the Subnet ID. To apply the subnet mask to the entire network address, a binary AND operation is performed. AND operations work by assuming that output is "true" if both inputs are "true." If not, "false" is returned.

This generates the Subnet ID. Routers use the Subnet ID to figure out the most efficient route between different subnetworks.

Refer to the illustration of generating a subnet mask for further information.

To build variable-length subnets, we use permutations on the number of bits reserved for subnet creation. This is referred to as Variable Length Subnet Masking (VLSM).

A subnet’s broadcast address is determined by setting all of the remaining bits of Host Id as’1′ after some bits are reserved to represent the subnet.

See the below image of the Broadcast Address.

Example of Subnetting

Let’s look at a simple situation to better grasp subnetting. A small organization is divided into four departments: the technology department, the sales and marketing department, the finance department, and the HR department. Every department has 50 employees. The organizations made use of a private class C IP network (with network ID If there is no subnetting, all computers will operate in a single large network. It becomes difficult for the network administrator to manage the task because if he broadcasts a message to the system, it will be forwarded to all departments. Subnetting is used to solve this type of difficulty.

After subnetting, the network will look something like this:

Uses of Subnetting in Computer Networks

Subnetting in computer networks has several uses, including:

  • Efficient use of IP addresses: Subnetting allows for the creation of smaller networks within a larger network, which helps to conserve IP addresses.
  • Improved network performance: By creating smaller networks, subnetting can help reduce network traffic and improve overall network performance.
  • Enhanced security: Subnetting can improve network security by separating different parts of the network into smaller subnetworks, making it harder for unauthorized access.
  • Flexibility: Subnetting allows for the creation of networks of different sizes, depending on the specific needs of the organization.
  • Routing efficiency: Subnetting can improve routing efficiency by allowing routers to route traffic directly to the appropriate subnet instead of broadcasting it to the entire network.
  • Improved fault tolerance: Subnetting can help improve fault tolerance by isolating network problems to specific subnets and preventing them from affecting the entire network.

Advantages of Subnetting in Computer Networks

There are several advantages of subnetting in computer networks, including:

  • Better Organization and Management: Subnetting allows network administrators to divide a larger network into smaller, more manageable subnets. This makes it easier to allocate resources, troubleshoot network issues, and manage network traffic.
  • Improved Network Performance: Subnetting can improve network performance by reducing network congestion and limiting the amount of broadcast traffic on the network. With smaller subnets, broadcast traffic is limited to only the devices on that subnet, reducing the overall amount of network traffic.
  • Enhanced Security: Subnetting improves network security by isolating traffic between subnets and restricting access to sensitive information. This makes it more difficult for unauthorized users to access sensitive data or launch attacks on the network.
  • More Efficient Use of IP Addresses: By dividing a larger network into smaller subnets, network administrators can make more efficient use of IP addresses. This is particularly important as the number of devices connected to the network continues to grow.
  • Flexibility: Subnetting provides network administrators with greater flexibility in how they manage their networks. They can allocate resources more efficiently, troubleshoot issues more effectively, and make changes to the network more easily.

Overall, we can confidently say subnetting in computer networks is valuable for network administrators.

Disadvantages of Subnetting in Computer Networks

Although there are several advantages of subnetting, there are also some potential disadvantages of subnetting in computer networks that network administrators should consider:

  • Increased Complexity: Subnetting can add complexity to network design and configuration, which can make it more difficult for network administrators to manage the network.
  • Requires Additional Resources: Subnetting requires additional resources such as routers and switches, which can increase the cost of building and maintaining the network.
  • Risk of Misconfiguration: Subnetting requires careful planning and configuration to ensure that subnets are properly set up and configured. Misconfiguration can lead to network issues, security vulnerabilities, and other problems.
  • Reduced Broadcast Capability: By dividing a network into smaller subnets, the overall broadcast capability of the network is reduced. This can make it more difficult to broadcast messages to all devices on the network.
  • Potential for Subnet Overlap: If subnets are not properly designed and configured, there is a risk of subnet overlap, which can lead to network issues and security vulnerabilities.

In conclusion, subnetting in computer networks involves dividing a large network into smaller sub-networks. Subnetting enables efficient utilization of IP addresses, improves network performance, and enhances network security. Additionally, subnetting reduces network congestion, provides flexibility in network design, and allows for efficient routing of network traffic. However, subnetting requires careful planning, and proper addressing, and can increase network complexity, which can be a disadvantage in some cases.


Here are some frequently asked questions on subnetting in computer networks:

Q1: Why do we need subnetting in computer networks?
Ans: We need subnetting in computer networks to improve network performance, manage network traffic, and enhance network security. Subnetting also allows us to conserve IP address space by using smaller, more efficient subnets.

Q2: What is the difference between a network address and a host address?
Ans: A network address is the portion of an IP address that identifies the network, while the host address identifies the specific host or device on the network. In subnetting, the network address and host address are separated by the subnet mask.

Q3: How does subnetting in computer networks improve performance?
Ans: Subnetting improves network performance by reducing the size of broadcast domains and limiting the scope of network traffic. This can improve network efficiency and reduce network congestion.

Q4: What is the difference between static and dynamic IP addressing?
Ans: Static IP addressing involves manually assigning a fixed IP address to a device on the network, while dynamic IP addressing involves automatically assigning IP addresses to devices using a DHCP server.

Q5: What is a default gateway?
Ans: A default gateway is a router or other device on a network that serves as the entry and exit point for all network traffic to and from devices on the network. The default gateway is responsible for forwarding network traffic between subnets and to the internet.

Q6: What is a VLAN?
Ans: A VLAN, or Virtual Local Area Network, is a logical grouping of devices on a network that allows network administrators to segment network traffic and improve network performance and security.

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