Subnet Explained: What is it & how does it work

Effective network management is key for ensuring smooth operations as organizations expand and technology advances increasing the demand for efficient networking solutions. One of the most effective ways to organize large networks is through subnetting, a technique that simplifies traffic management, boosts security, and provides scalability.

In this article, we’ll dive into what subnets are, how they work, and why they’re a valuable tool for businesses of all sizes.

Key takeaways:

Subnets break large networks into smaller, more manageable sections, making it easier to control data flow and enhance performance
They improve traffic management and network security, enabling organizations to isolate issues and maintain operational integrity

What is a subnet?

A subnet (short for subnetwork) is a smaller, more manageable section of a larger network. It breaks down a bigger network into smaller segments, simplifying data flow management.

By creating subnets, organizations can better control traffic across their networks. Instead of having all devices communicating over one large, congested network, subnetting allows the creation of smaller “traffic lanes”.

This segmentation improves efficiency by ensuring that data moves within a subnet rather than congesting the entire network. With the proper design and implementation of subnets, organizations can mitigate potential traffic issues before they escalate into larger problems.

Subnetting also enhances traffic management by reducing the size of broadcast domains—the area in a network where broadcast traffic is sent. Broadcast traffic, a type of communication sent to all devices in a network segment, can create unnecessary congestion if not managed correctly. With fewer devices receiving broadcasts, networks can process data faster and reduce unnecessary load, leading to smoother operations and ultimately enhancing performance and user satisfaction.

Aspect	Without Subnet	With Subnet
Traffic Management	Complex	Simplified
Security	Harder to manage	Easier to isolate risks
Scalability	Limited	More scalable

Why use subnetting?

Subnetting is essential for modern network design, providing clear advantages in terms of performance, security, and scalability. It breaks large networks into smaller, manageable sections, making them easier to operate and maintain. Here’s a closer look at the main reasons why organizations rely on subnetting:

Reduced network congestion

One of the main reasons to use subnetting is to cut down on network congestion. In large networks with many devices, traffic can pile up, leading to slow performance and downtime. As network demands grow, the risk of bottlenecks increases.

By limiting the number of devices that communicate within each subnet, organizations can lighten the load on the network. This leads to smoother data transfer and reducing the likelihood of interruptions. The result? Faster response times and a better experience for users, particularly in environments with high traffic loads.

For instance, consider a university campus with thousands of connected devices. By creating subnets for different departments, the university can manage data traffic more efficiently, ensuring that each department operates without interference from others.

Enhanced security

Subnetting also enhances security by isolating different sections of a network. If a security breach occurs, organizations can contain the problem within the affected subnet, preventing it from spreading to the rest of the network. This containment strategy is critical for businesses handling sensitive data, such as financial institutions.

By segmenting critical systems – such as payment processing and customer databases – into separate subnets, banks can ensure that a breach in one area doesn’t compromise the overall security. This strategic isolation not only protects sensitive data but also makes it easier to comply with industry regulations.

Improved scalability

As businesses grow, they need to adapt their networks to support new devices, locations, and services. Subnetting helps organizations expand their networks in a smart and efficient way. For instance, in the healthcare sector, hospitals can use subnetting to keep sensitive patient data isolated within dedicated subnets.

This kind of compartmentalization not only helps limit the potential spread of security breaches but also ensures that different departments, such as radiology and administration, can operate independently and efficiently. For businesses that anticipate future growth or changes in technology, this flexibility is crucial.

On top of that, subnetting offers a whole range of other advantages that can significantly enhance how organizations manage their networks more effectively:

Efficient IP address management
Subnetting enhances network performance in several ways. One key benefit is that it enables efficient IP address management by dividing large address spaces into smaller segments. This is particularly helpful for organizations with multiple departments or locations, as it ensures logical allocation of addresses with minimal waste. By implementing subnetting, organizations can optimize IP address use, which is especially important given the limited nature of IPv4 addresses.
Improved performance in busy environments
In busy settings like data centers, subnetting boosts performance by reducing unnecessary traffic within the network. By limiting the size of broadcast domains, only the relevant devices within each subnet receive broadcast traffic. This results in freed up bandwidth and improved response times, leading to a more efficient and responsive network.
Improved failure recovery
Subnetting also helps with quick recovery from network failures. By isolating different network segments, businesses can contain and address issues without impacting the entire system. For instance, if a server in one subnet fails, other subnets can continue to operate independently. This capability significantly minimizes downtime and ensures that critical operations remain uninterrupted, which is vital for maintaining service continuity.

To determine whether subnetting is beneficial for your business, it’s important to assess your current network needs. Consider factors such as the size of your network, the amount of traffic you handle, security requirements, and any plans for future expansion.

By evaluating these aspects, you’ll be better equipped to decide whether subnetting can improve your network’s efficiency and future-proof your network.

How does subnetting work?

Subnetting divides an IP address into two distinct parts: the network prefix and the host identifier. The network prefix identifies the specific subnet within a larger network, while the host identifier indicates the individual device within that subnet.

This division simplifies IP management, improving routing and data transfer within networks.

To implement subnetting effectively, one must understand the concept of subnet masks. A subnet mask is a 32-bit number that helps determine which portion of an IP address is designated for the network and which part is allocated to the host.

By using a subnet mask, network administrators can control the size of a subnet and define how many devices can connect to it. For example, in the IP address 192.168.1.1 with a subnet mask of 255.255.255.0, the first 24 bits (the network portion) are used to identify the subnet, while the remaining 8 bits (the host portion) are used for individual devices within that subnet.

How to subnet an IP address effectively

Here’s a step-by-step guide:

Identify the network size:
Determine the number of hosts and devices that will be part of the network – this is crucial for understanding how large your subnets need to be. Having a clear idea of the number of devices that will connect to the network, enables administrators to make informed decisions about subnet allocation.
Choose the subnet mask:
Based on the required size, select an appropriate subnet mask. For instance, a /24 subnet mask allows for 256 addresses (including the network and broadcast addresses), making it suitable for networks with up to 254 usable IP addresses. Choosing the right subnet mask is essential to ensure that there are enough addresses available for all devices while minimizing wasted addresses.
Apply the subnet mask:
Divide the IP address range into subnets by applying the chosen subnet mask. This process involves configuring routers and switches to recognize the subnet structure. With the correct configuration, data packets are routed efficiently, which boosts network performance and ensures smooth communication across the system.
Assign IP addresses:
Allocate specific IP addresses to devices within each subnet. Ensure that each device has a unique IP address to avoid conflicts. Proper IP allocation is essential for maintaining seamless communication within the network, as duplicate IP addresses can cause conflicts and result in connectivity issues.

To simplify the subnetting process and reduce the likelihood of errors, it’s highly recommended to use subnet calculators.

These tools can quickly determine subnet masks, available addresses, and other relevant information, making the whole process smoother and more precise. Many online tools offer user-friendly interfaces that allow administrators to simply enter their IP addresses and quickly calculate the necessary details.

In short, it’s important to understand the specific needs of your organization when considering subnetting.

Let’s take the following use case: a small office might only need a few subnets, allowing for straightforward management and minimal configuration; on the other hand, a large enterprise may require numerous subnets to accommodate various departments, locations, and services, leading to a more complex setup.

Common subnetting terminologies

Understanding the terminology associated with subnetting facilitates network management. An IP address uniquely identifies each device on a network, similar to a phone number. It enables devices to communicate with each other and access the internet, with a typical IPv4 address appearing as 192.168.1.1.

A subnet mask is a 32-bit number used to distinguish the network portion from the host portion of an IP address. It defines which part of the IP address refers to the network and which part refers to the individual device.

For example, a common subnet mask for a small network is 255.255.255.0, which corresponds to a /24 CIDR notation. This means that the first 24 bits of the address are used for the network, while the last 8 bits are available for host devices.

CIDR (Classless Inter-Domain Routing) is a method of IP address allocation and subnetting that allows for a more efficient use of IP addresses. Instead of relying on traditional classes (A, B, C), CIDR offers a more flexible approach, represented as an IP address followed by a slash and a number (e.g., 192.168.1.0/24).

The number indicates how many bits are used for the network prefix, allowing for varied subnet sizes and better address management.

The broadcast address is utilized to communicate with all devices in a subnet simultaneously. It’s akin to sending a group text message to everyone in your contact list at once. For instance, if your subnet is 192.168.1.0/24, the broadcast address would be 192.168.1.255.

This address allows for efficient communication to all devices within that subnet without needing to address each device individually.

Let’s take the following analogy and position a subnet as different sections in a library:

Each section (subnet) contains books on a specific topic (devices) but all belong to the same library (the larger network);
The IP address is like the specific shelf where a book resides, while the subnet mask determines how many shelves can fit within each section;
The CIDR notation indicates how many sections are organized together for efficient access, and the broadcast address functions like an announcement made within the library, reaching all patrons in that specific section.

Glossary

IP address: Unique identifier for devices (e.g., 192.168.1.1).
Subnet mask: Defines network vs. host portions (e.g., 255.255.255.0).
CIDR (Classless Inter-Domain Routing): Flexible IP allocation method (e.g., 192.168.1.0/24).
Broadcast address: Communicates with all devices in a subnet (e.g., 192.168.1.255).

Benefits of subnetting

As covered previously, subnetting offers several significant advantages that improve both the network efficiency and security.

One of the primary benefits is improved security – by isolating sections of the network, subnetting makes it easier to contain and manage potential security breaches. If an attack occurs within one subnet, it can be contained without compromising the entire network, thereby reducing the spread of attacks and minimizing damage.

Another key advantage is better traffic management. Subnetting limits the size of broadcast domains, which helps reduce unnecessary traffic and helps prevent bandwidth overload. This leads to faster data transfer and more efficient network performance.

In addition, subnetting improves overall performance by optimizing the use of available IP addresses. With more efficient IP address, there’s less waste, allowing organizations to maximize their resources and maintain a well-organized network.

Lastly, subnetting provides scalability, making it easier for businesses to expand and manage a growing network. As businesses evolve, subnetting allows for the seamless addition of new devices or departments without overwhelming the existing infrastructure.

To reap the full benefits of subnetting, businesses should regularly review and adjust their subnet structures as their networks grow. This proactive approach ensures that the network remains efficient and secure, adapting to the changing needs of the organization.

Case study: The University of California, Berkeley

A compelling example of effective subnetting can be found at the University of California, Berkeley. To tackle network congestion and security concerns due to an increasing number of connected devices, the university adopted a subnetting strategy to isolate different departments.

By dividing its network into subnets for various areas – like the School of Engineering and the School of Law – UC Berkeley significantly boosted both network performance and security.

This approach not only reduced broadcast traffic but also allowed each department to implement tailored security measures to safeguard sensitive information.

As a result, the network became more efficient, and capable of handling the diverse needs of users while maintaining high levels of security. This successful implementation of subnetting at UC Berkeley highlights how smart network design can lead to improved operational efficiency.

You can learn more about UC Berkeley’s approach to subnetting and network security in their Protected Subnet Guideline (Berkeley Security).

Subnet masking and CIDR notation

Subnet masks are key to identify the network and host portions of an IP address – an IP address is a 32-bit number, and the subnet mask defines which bits are used for the network prefix and which is for the host identifier.

For example, in the IP address 192.168.1.1 with a subnet mask of 255.255.255.0, the first 24 bits (the network portion) are used to identify the subnet, while the remaining 8 bits (the host portion) are for individual devices within that subnet.

CIDR notation is a method used in IP address allocation that improves the flexibility and efficiency of IP addressing. CIDR notation combines the IP address with a suffix that indicates the number of bits in the network prefix.

For instance, the notation 192.168.1.0/24 signifies that the first 24 bits are designated for the network, allowing for up to 256 addresses in that subnet. This system has largely replaced the older class-based system, providing more efficient use of IP addresses and enabling better routing.

Step-by-step process

Understand the basics:
Recognize how IP addresses are divided into binary – an IP address consists of four octets (e.g., 192.168.1.1), each ranging from 0 to 255. In binary form, this translates to 32 bits (e.g., 11000000.10101000.00000001.00000001).
Apply CIDR notation:
Learn how CIDR helps in flexible IP address allocation – for example, a /24 subnet allows for 256 total addresses (including network and broadcast addresses), while a /16 subnet allows for 65,536 addresses. Understanding CIDR notation enables more granular control over how IP addresses are assigned, helping prevent address exhaustion and ensuring that organizations can scale their networks appropriately.
Calculate subnet masks:
Break down the IP address and subnet mask using binary to understand how many subnets you can create. Convert the subnet mask to binary (e.g., 255.255.255.0 becomes 11111111.11111111.11111111.00000000) and count the number of consecutive ones (1s) to determine the subnet size.

There are numerous online resources and calculators available to support learning CIDR. Tools like Subnet Calculators allow users to input an IP address and subnet mask to see the number of available subnets and hosts, helping clarify the concepts further. By mastering subnet masks and CIDR notation, network administrators can optimize their IP address allocation strategies, enhance routing efficiency, while ensuring effective network management.

Types of subnetting

When it comes to subnetting, network administrators have several options to choose from to optimize network performance and management. The main types include fixed-length subnetting, variable-length subnetting, and subnetting with CIDR. Each one meets different needs and has its advantages and disadvantages, which are outlined in the comparison table below.

Fixed-length subnetting:

In fixed-length subnetting, all subnets are the same size. This method simplifies network management since each subnet has an equal number of available addresses, making it easier to allocate resources. However, it can lead to inefficient use of IP addresses if some subnets require more addresses than others.
This inefficiency may result in wasted IP addresses, especially in organizations with varying needs across departments or locations.

Variable-length subnetting (VLSM):

Variable-length subnetting allows for subnets of different sizes, tailored to the specific needs of each network segment. This approach maximizes the efficient use of IP addresses, as it allocates only only the number of addresses required for each subnet.
For example, a small department might only need a few IP addresses, while a larger department may require a much larger pool. This flexibility enables organizations to allocate resources where they’re most needed. However, VLSM can complicate network management due to the varying sizes of each subnet.
Network administrators must keep track of these different subnet sizes, which can add complexity to configuration and monitoring tasks. This extra layer of complexity requires more diligent documentation and potentially more advanced management tools to ensure all devices are correctly configured.

Subnetting with CIDR:

CIDR is a modern method of subnetting that offers flexible allocation of IP addresses without being restricted to the traditional class-based system. It allows network administrators to create subnets of various sizes by using a notation (e.g., /24, /16) to indicate how many bits are used for the network prefix. This flexibility optimizes IP address utilization and improves routing efficiency.
For example, CIDR notation allows for the creation of very small subnets when necessary, which can be particularly helpful in managing the IP address space in organizations with diverse needs across different departments.

Type of Subnetting	Description	Pros	Cons
Fixed-Length Subnetting	Subnets are all the same size.	Simplifies network management and planning.	May waste IP addresses if some subnets need more.
Variable-Length Subnetting (VLSM)	Subnets can vary in size according to need.	Optimizes IP address usage, allowing efficient allocation.	More complex to manage due to varying subnet sizes.
Subnetting with CIDR	Flexible IP allocation without traditional class constraints.	Improves routing efficiency and maximizes address space.	Requires understanding of CIDR notation, which can be complex for beginners.

Subnetting tools and resources

When it comes to managing subnets effectively, several tools can help streamline the process and minimize errors.

These tools are essential for network administrators who want to optimize IP address allocation and efficiently manage their network infrastructure efficiently.

Subnet calculators

Subnet calculators are invaluable tools that automatically calculate subnets based on the provided IP address and subnet mask.
These calculators help network administrators quickly determine how many addresses are available within a subnet, the range of usable IP addresses, and the broadcast address.
This eliminates the manual calculations that can lead to errors, making subnet management much more efficient.
Some online subnet calculators include Subnet-Calculator.com ,IPCalc, UptimeRobot Subnet Calculator which offer user-friendly interfaces for quick calculations – these allow users to input their specific parameters and receive instant feedback, significantly reducing the potential for human error during the configuration process.

IP address management (IPAM) tools

IPAM tools are designed to help organizations keep track of IP addresses and subnet allocations.
These tools provide comprehensive visibility into IP address usage across the network, allowing administrators to monitor available addresses, plan for future needs, and avoid conflicts.
Solutions like SolarWinds IP Address Manager and ManageEngine OpUtilsoffer robust features for managing IP addresses, including visualization tools, alerts for conflicts, and reporting capabilities.
By leveraging these tools, organizations can ensure that their IP address allocations are organized, helping to streamline the management process and enhance overall operational efficiency.

By using these subnetting tools and resources, network administrators can enhance their operational efficiency, reduce the chances of misconfigurations, and maintain better control of their network infrastructure. This ensures networks stay organized, scalable, and ready to meet the evolving needs of the organization.

Conclusion

In summary, subnetting is essential for managing networks effectively, making a big difference in both efficiency and security. By breaking down IP address spaces into smaller, manageable parts, businesses can cut down on congestion, boost performance, and strengthen security.

By implementing the strategies outlined in this article, network administrators can build networks that are not only more efficient and secure, but also scalable enough to keep up with today’s fast-paced tech landscape. Subnetting isn’t just a technical requirement — it’s a key advantage for organizations that want to succeed in an increasingly complex digital world.

Remember these key points of the article:

Benefits of subnetting: Improved security, better traffic management, enhanced scalability, and optimized IP address usage.
Types of subnetting: Fixed-length subnetting, variable-length subnetting (VLSM), and CIDR, each serving different organizational needs.
Useful tools: Subnet calculators and IPAM tools are vital resources for managing IP address allocation and improving network performance.

What is a subnet?

Why use subnetting?