Updated on 11th Dec, 23 9.1K Views

This blog explores the concept of subnetting,  its structure, types, IPv4 and IPv6 addressing and creation methods, functionality, applications, advantages, and drawbacks. It offers a comprehensive view of subnetting principles.

Table of Contents

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What is a subnet?

A subnet, or subnetwork, divides a larger network into smaller parts. This division helps in managing network resources efficiently. Subnets have unique IP address ranges. They are created to improve network performance, security, and traffic control. Subnetting allows administrators to allocate resources effectively, enhance security in specific segments, and optimize overall network functionality. By organizing devices into smaller groups, it facilitates better control and management of network traffic.

Structure of Subnet

The structure of a subnet involves dividing a larger network into smaller, more manageable sections known as subnets. Each subnet has its own unique range of IP addresses. For instance, consider a network with the IP address range 192.168.0.0/16. Subnetting this network involves splitting it into smaller parts by borrowing bits from the host portion of the IP address.

Let’s use an example: If we have the IP address 192.168.0.0/24, which represents a network with 256 available IP addresses (ranging from 192.168.0.1 to 192.168.0.254), subnetting allows us to divide this into smaller subnets. For instance, using subnetting, we can create two subnets by borrowing bits from the host portion. By splitting the /24 subnet into two /25 subnets, we will have subnets like 192.168.0.0/25 and 192.168.0.128/25, each with 128 available IP addresses. This breakdown allows for more efficient use of IP addresses and better network management.

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Types of Subnets

These types of subnets serve different purposes in networking, offering flexibility, efficiency, and better IP address management based on specific requirements. Here are the various types which are as follows:

  • Public Subnet: This subnet type provides a direct route to an internet gateway. Resources inside a public subnet can access the internet without any hindrance. These subnets are commonly used for resources that require public accessibility, such as web servers or load balancers.
  • Private Subnet: In contrast to a public subnet, a private subnet lacks a direct route to an internet gateway. Resources within a private subnet cannot access the internet directly. Instead, they require a Network Address Translation (NAT) device to access the public internet. Private subnets are used for sensitive resources like databases or application servers that don’t need public accessibility.
  • VPN-Only Subnet: This subnet type is configured with a route to a site-to-site VPN connection through a virtual private gateway. However, it lacks a route to an internet gateway. Resources within this subnet cannot access the internet directly but can communicate securely through a VPN connection.
  • Isolated Subnet: An isolated subnet lacks routes to destinations outside its Virtual Private Cloud (VPC). Resources within an isolated subnet can only communicate with resources within the same VPC and cannot access the internet or connect to resources outside the VPC. This type of subnet ensures complete isolation and enhanced security for specific resources.

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What is Subnet Masking?

Subnet masking is a technique used in computer networking to divide an IP address into two separate parts: the network address and the host address.  This process enables the efficient addressing and routing of data packets within a network. This mask helps in identifying the network portion of an IP address by indicating which bits represent the network and which bits represent the host within a given network.

IP addresses are of two types IPv4 and IPv6 addresses, let’s understand these in depth as these are important to understand because without IP addresses we are not able to identify any entity inside any network.

IPv4 Addressing

IPv4 addressing is the system used to assign unique numerical identifiers to devices participating in a computer network that uses the Internet Protocol version 4 (IPv4). IPv4 addresses are 32-bit numerical addresses written in decimal format, consisting of four sets of numbers separated by periods (for example, 192.168.1.1). However, due to the rapid growth of the internet, the number of available IPv4 addresses has become limited.

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IPv6 Addressing

IPv6 addressing is an advanced and enhanced version of the Internet Protocol (IP) designed to succeed IPv4. It uses a 128-bit hexadecimal address format, providing a significantly larger pool of unique IP addresses compared to IPv4. IPv6 addresses are represented as eight groups of four hexadecimal digits separated by colons.

For example, 2001:0db8:85a3:0000:0000:8a2e:0370:7334. The adoption of IPv6 is driven by the need for more available IP addresses to accommodate the growing number of devices connected to the internet.

How Does Subnetting Works

Subnetting makes the management of IP addresses easy, reduces network congestion, and enhances security by segmenting the network into smaller parts. Following are the steps for how subnetting works:

Determining the Network: Initially, the IP address and subnet mask are used to identify the network and host parts of the address. The subnet mask designates which portion of the IP address belongs to the network and which part belongs to the host.

Dividing into Subnets: Subnetting involves borrowing bits from the host portion of the IP address to create subnets. By doing this, it increases the number of networks while reducing the number of hosts within each subnet.

Calculating Subnet Masks: Each subnet is assigned its own subnet mask, which further divides the network into smaller sub-networks. Subnet masks determine the range of IP addresses available for hosts within each subnet.

Assigning Addresses: Finally, IP addresses are allocated to devices within each subnet based on the subnet mask. This allows for efficient utilization of IP addresses and aids in organizing devices logically within the network.

Let’s Understand with the help of one example, how we  can divide any network into smaller subnetworks:

Step 1: Determine the IP Address and Default Subnet Mask:

IP Address: 192.168.1.0

Default Subnet Mask: 255.255.255.0 (or /24)

Step 2: Decide  Subnet Mask for Subnetworks:

 Let’s divide this network into 4 subnetworks. For this, we need 2 subnet bits (2^2 = 4).

Step 3: New Subnet Mask:

  • Default mask: 255.255.255.0 (or /24)
  • Updated mask: 255.255.255.192 (or /26) – We borrowed 2 bits for subnetting.

Step 4 :Determine the Number of Subnets and Hosts:

2 subnet bits allow having 4 subnets (2^2 = 4) .With 6 host bits remaining (32 – 26 = 6), each subnet can accommodate 62 hosts (2^6 – 2 = 62 – subtract 2 for network and broadcast addresses).

Step 5 :Define the Subnet Bits and Host Bits:

  • Subnet bits: 192.168.1.[Network].[Subnet]. [Host]
  • Host bits: The last 6 bits in the fourth octet are for hosts.

Step 6 : Calculate Subnet IDs and Ranges:

  • Increment value for subnet IDs: 192.168.1.0, 192.168.1.64, 192.168.1.128, 192.168.1.192
  • Usable IP range for each subnet:

  Subnet 1: 192.168.1.1 to 192.168.1.62

  Subnet 2: 192.168.1.65 to 192.168.1.126

  Subnet 3: 192.168.1.129 to 192.168.1.190

  Subnet 4: 192.168.1.193 to 192.168.1.254

Step 7 : Assign Addresses to Subnets:

   Allocate the determined IP ranges to each respective subnet without overlap.

Step 8 : Configure Devices and Routing:

 Update the subnet mask on devices within each subnet and configure routing to recognize the newly subnetted network.

Types of Subnet Classes

There are two types of subnet classes through which we can do subnet masking. The primary purpose of classful subnet masking was to group IP addresses into fixed classes with predefined subnet masks. While classless subnet masking (CIDR) introduced a more flexible approach, enabling the efficient allocation and management of IP addresses by using variable-length subnet masks and route aggregation techniques:

  • Classful Subnetting

Classful subnetting is a method of subnetting that uses the three classes of IP addresses to determine the subnet mask. The three classes of IP addresses are:

Class A: 10.0.0.0 – 127.255.255.255

Class B: 128.0.0.0 – 191.255.255.255

Class C: 192.0.0.0 – 223.255.255.255

The default subnet mask for each class is:

Class A: 255.0.0.0

Class B: 255.255.0.0

Class C: 255.255.255.0

  • Classless Subnetting (VLSM)

Classless subnetting (VLSM) is a method of subnetting that allows for more flexibility in subnet design. VLSM does not use the three classes of IP addresses to determine the subnet mask. Instead, it uses a subnet mask that is specific to the network.

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Application of Subnetting

In all these applications, subnetting enables efficient IP address allocation and enhances security by creating isolation between segments, which helps in performance optimization and management of hosts. Here are some applications of subnetting:

  • Corporate Networks: In large corporations, subnetting assists in organizing networks by separating different departments or floors into distinct subnets. This segmentation helps manage traffic, implement security policies, and simplify network administration.
  • Internet Service Providers (ISPs): ISPs use subnetting to allocate IP addresses to their customers more effectively. By partitioning their address spaces into smaller subnets, ISPs can efficiently assign addresses based on specific requirements while conserving IP addresses.
  • Data Centers: In data centers, subnetting is crucial for creating isolated segments for different purposes. For instance, separate subnets can be designated for storage, web servers, databases, or virtual machines. This isolation enhances security and streamlines network management.
  • Virtual Private Networks (VPNs): Subnetting plays a role in VPNs, allowing organizations to create private networks over the internet securely. VPNs utilize subnetting to partition IP spaces, ensuring that different branches or remote offices can communicate while maintaining network privacy.
  • Cloud Computing: Cloud service providers implement subnetting to manage resources efficiently. They segment their infrastructure into various subnets to separate different types of services, ensuring better security, resource utilization, and network performance.
  • Home Networks: Even in home networks, subnetting can be utilized. For instance, a home router might create separate subnets for guest networks, IoT devices, and personal devices, providing a level of isolation and security between these networks.

Benefits of Subnetting

Subnetting is a fundamental part of network design that significantly helps in address management, enhancing security, and streamlining network performance. Subnetting offers several benefits in network management and administration:

  • Efficient IP Address Utilization: Subnetting allows the allocation of IP addresses more efficiently by dividing large networks into smaller subnets. This process helps prevent address wastage and optimizes address space utilization.
  • Enhanced Network Performance: Smaller subnets facilitate reduced network congestion by segmenting traffic. It helps in isolating broadcast domains and limiting the scope of broadcast traffic, leading to better network performance and response times.
  • Improved Security: Subnetting assists in implementing security measures by segregating network segments. Access controls, firewalls, and security policies can be more effectively applied to specific subnets, minimizing security threats and unauthorized access.
  • Simplified Network Management: Managing smaller subnets is more manageable and less complex than administering a large, flat network. It enables easier troubleshooting, maintenance, and configuration changes, simplifying overall network management.
  • Scalability: Subnetting supports network scalability by offering flexibility in accommodating new devices or expanding network infrastructure. It allows for the creation of new subnets without major changes to the existing network architecture.
  • Better Traffic Control: Subnetting helps in controlling and directing network traffic more effectively. Network administrators can prioritize and route traffic based on specific subnet requirements, optimizing data flow within the network.
  • Improved Organization and Structure: Subnetting enables better organization of networks based on departments, functions, or geographic locations. It offers a structured approach to network design, enhancing overall efficiency and management.

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Limitations of Subnetting

Understanding these limitations helps network administrators and engineers make informed decisions while implementing subnetting in networks : 

  • Complex Network Structure: As the number of sub-networks increases, the overall network complexity also rises, making it more challenging to manage and troubleshoot network issues.
  • Unused IP Addresses: Subnetting can lead to the creation of sub-networks with surplus IP addresses, resulting in many addresses remaining unused or wasted.
  • Hardware Dependency: Efficient communication among sub-networks often requires additional hardware components like routers or switches, increasing the dependency on these devices for continuous data exchange.

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Conclusion

In conclusion, subnetting serves as a fundamental tool for optimizing network functionality by dividing larger networks into smaller, manageable segments. It enables efficient IP address utilization, enhances network security, and streamlines data transmission. While it presents complexities and challenges, understanding its principles empowers effective network management and facilitates scalable, efficient communication across diverse systems.

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