Foundations of Subnetting

Why Should You Care About Subnetting?

Ever wondered how your data knows exactly where to go when you visit a website, send an email, or watch a video online? With millions of devices connected to the internet, it’s not magic — it’s smart organization. And subnetting plays a big role in that.

Think of a large hotel. Each floor might represent a network, and every room on that floor is assigned to a guest. Without a room number, the hotel staff wouldn’t know where to deliver your breakfast or clean the sheets. In the same way, subnetting divides big networks into smaller, more manageable “floors” (or sub-networks), so data can travel smoothly to its correct “room” — your device.

But subnetting isn’t just about order. It’s about efficiency and security. Without it, internet traffic would be chaotic, devices would have trouble finding each other, and managing large networks (like those in corporations or ISPs) would be nearly impossible.

So whether you're a tech beginner, a student, or just curious, understanding how subnetting works will help you see the hidden structure behind how data flows — and how the internet stays organized behind the scenes.

What Is Subnetting?

Subnetting is the process of dividing a large network into smaller, more manageable sections called subnets. This makes it easier to control traffic, organize devices, and improve efficiency.

Think of a city broken into districts — it’s easier to manage traffic, mail delivery, and services when everything is grouped by neighborhoods. Subnetting works the same way in networks: instead of one big, chaotic space, you have clearly defined “districts” for different devices or teams.

Technically speaking, subnetting allows network administrators to split up an IP address range into smaller chunks. This reduces congestion, limits unnecessary traffic, and makes large networks easier to secure and troubleshoot.

We’ll break down subnet masks and CIDR notation next — but if you’re not yet familiar with how IP addresses work, check out our article: What Is an IP Address?

In short, subnetting helps networks scale, stay organized, and perform better.

Subnet Masks: The Address Filter

When talking about subnetting, it's important to understand that every IP address is logically split into two main parts:

• The network part – which identifies the specific network the device belongs to (or subnet)
• The host part – which identifies the specific device (computer, phone, printer, etc.) within that network

Together, these two parts help devices understand:

• Which network they are part of
• Where to send data when communicating with devices in the same or different networks

This split is defined by something called a subnet mask — and understanding how it works gives us insight into how devices talk to each other and how networks are structured.

Binary Breakdown of an IP Address and Subnet Mask

Let’s break it down step by step with an example:

• IP address: 192.168.1.0
• Subnet mask: 255.255.255.0

Component	Decimal	Binary
IP Address	192 . 168 . 1 . 0	11000000 . 10101000 . 00000001 . 00000000
Subnet Mask	255 . 255 . 255 . 0	11111111 . 11111111 . 11111111 . 00000000

Need a refresher on how IP addresses look in binary and why it matters? Check out our article on IP Address Evolution

What’s Happening Here?

• Each "1" bit in the subnet mask means “this part is reserved for the network.”
• Each "0" bit means “this part is available for hosts inside the network.”

In this example:

• The first 3 sections (called octets) are all 255, or 11111111 in binary.
• That’s 24 active bits – all reserved for the network portion.
• The final section is 0, or 00000000, which is available for host devices.

This gives us a range of host IPs from 1 to 254 (we’ll explain why not 0 or 255 below).

How the Host Range Works

In the last section (octet), 256 total values are possible – from 0 to 255, a total of 256.

But… as we mentioned previously, 0 and 255 cannot be used for hosts:

• 192.168.1.0 = Network Address – identifies the subnet itself
• 192.168.1.255 = Broadcast Address – used to send a message to every device on the same local network

That leaves us with:

• Usable IP addresses: 192.168.1.1 to 192.168.1.254
• These are the IPs that can be assigned to real devices like your laptop, smart TV, or phone.

This mask tells the device that the first three octets (192.168.1) are the network and the last part (the final 0) is where the host lives. This means that:

• All devices with an address like 192.168.1.X are in the same network
• X can range from 1 to 254 — those are the host addresses
• .0 is the network address
• .255 is the broadcast address used for sending to all devices on the network

Broadcast = Like a Radio Transmission

When a device sends a broadcast message, it uses the .255 address to say:
“Hey everyone on this network, listen up!”

It’s just like tuning into a radio station — if your device is “tuned” to the same frequency (in this case, the same network), it will receive the message.

Only devices that belong to the same local network can “hear” the broadcast — just like only people tuned into the same radio station can hear the same music or news.

This is incredibly useful for automatic discovery — like when your phone instantly finds a nearby printer, or your smart TV detects your phone for screen mirroring.

CIDR Notation: IP Addresses Made Smarter

Before CIDR came into play, the internet used a system called Classful IP Addressing. This method grouped IP addresses into rigid categories called Classes — A, B, and C — each with a fixed number of networks and hosts.

But the class system had a big flaw: it led to wasted IP addresses.

Class-Based Addressing: The Old System

Before subnetting and CIDR notation were introduced, the internet relied on a rigid system called Classful Addressing. In this system, IP addresses were divided into fixed "classes" (A, B, and C), based on their starting IP range.

Here's how it used to work:

Note: The first octet (the first number in the IP address) determined the class.

While this system was easy to understand, it lacked flexibility. For example, if an organization needed 300 IPs, a Class C network (254 hosts) wasn’t enough, and a Class B (65,000+) was far too large — wasting tens of thousands of IPs.

Enter CIDR: Efficient and Flexible

CIDR (Classless Inter-Domain Routing) replaced the old, inefficient class-based system and made subnetting far more flexible.

Instead of fixed "Class A, B, or C" networks, CIDR uses a slash notation (like /24) to indicate how many bits are reserved for the network portion of the IP address — and how many are left for hosts.

This method allows network administrators to customize their networks based on actual needs, avoiding wasted IP addresses and simplifying routing.

Example: How CIDR Works

• CIDR Notation: 192.168.1.0/24
• /24 means 24 bits are reserved for the network
• 32 - 24 = 8 bits remain for host addresses
• 2⁸ = 256 total IPs → 254 usable (excluding .0 and .255)

This level of flexibility simply wasn’t possible under the old class-based system. With CIDR, you can efficiently assign IPs to departments, branches, or even individual devices depending on how many addresses they actually need.

CIDR Breakdown Table

CIDR ranges can go from /0 to /32, but most practical subnetting use cases for devices fall between /30 and /8.

Why CIDR Matters

CIDR maximizes address space and ensures your network can be right-sized to your needs — whether you're managing a home setup or a regional ISP. No more allocating thousands of IPs when you only need 50. It’s smarter, leaner, and built for the modern internet.

Why Subnetting Improves Network Efficiency

1. Reduces Broadcast Traffic

Without subnetting, every device on a network may hear messages not meant for them. Subnetting breaks a large network into smaller “neighborhoods” where broadcast messages stay local — reducing unnecessary traffic and improving speed.

2. Adds Network Isolation and Security

Subnetting lets you create boundaries. For example:

• Printers can be isolated in one subnet.
• Sensitive company data can stay in another.
• Guest Wi-Fi users can be separated from internal systems.

This structure makes it easier to control access and monitor traffic — helping prevent breaches and limit the spread of dangerous malware.

3. Makes Better Use of IP Addresses

Since private IP addresses are a limited resource, especially in large networks, it’s important to plan their usage wisely. Not every department, classroom, or office floor needs 254 IPs. Subnetting lets you assign only the number of addresses actually needed for each group — avoiding waste and making the most of available IPv4 space.

Hands-On Task

Now that you know how subnetting works, let’s see how it applies in your own home or office network.

Try This:

1. Check Your Current IP Address and Subnet Mask
   • On Windows: Open Command Prompt and type ipconfig
   • On macOS or Linux: Open Terminal and type ifconfig or ip a

   You’ll see something like:

   IP Address: 10.100.1.1
   Subnet Mask: 255.255.255.0

2. Use the Subnet Table Above

   Based on the subnet mask, figure out:

   • What’s the network range?
   • How many usable IPs are available for devices?

   In this example, with a subnet mask of 255.255.255.0, you have up to 254 usable addresses. That means your LAN can support up to 254 devices — from laptops and phones to smart fridges and TVs.

   Remember, there are actually 256 total addresses (2⁸). The first IP — 10.100.1.0 — is reserved to represent the network, and 10.100.1.255 is reserved as the broadcast address. Any message sent to 10.100.1.255 will be received by all devices in the same LAN.

3. Look Around Your Network

   Think about how many devices are actually connected in your home or office. You might be surprised how quickly IPs get used up — especially with smart devices, printers, and mobile phones.

Bonus Tip: What About My Public IP?

The IP address you just checked is your private IP — used only inside your Local Area Network (LAN). But when your data leaves the network and travels across the internet (WAN), your device uses a different public IP — assigned by your Internet Service Provider (ISP) and translated via a process called NAT (Network Address Translation).

This public IP is your digital footprint on the web.

Want to check your public IP address right now?
Click here to check your public IP address on ipseeker.io

This gives you the full picture of how private and public IPs work together — and why subnetting matters to everything you do online.

Real-World Examples of Subnetting

1. Office with Multiple Departments

Imagine a company has three departments: HR, Finance, and Engineering — each on a different floor.

Instead of putting all employees on one giant network (which could lead to traffic overload and security risks), the IT team subnets the network into three smaller ones:

• 192.168.10.0/26 for HR (up to 62 devices)
• 192.168.10.64/26 for Finance
• 192.168.10.128/26 for Engineering

Each department has its own subnet, making the network easier to manage and isolate. If someone downloads a large file in Engineering, it doesn’t slow down HR.

2. University Campus

A large university splits its network across faculties, dorms, and labs:

• Faculty networks are given larger subnets
• Dorm networks are limited to smaller IP ranges
• Labs are isolated for better security and equipment access

This setup lets IT assign bandwidth limits, monitor access, and protect sensitive systems — like exam databases — from student devices on the dorm Wi-Fi.

3. Smart Home

Your smart home might have 20+ connected devices: phones, smart TVs, speakers, thermostats, lights, and cameras.

If you're using a basic home router with the default 192.168.0.0/24 subnet, you have 254 usable IPs — more than enough for most households.

But advanced users might:

• Use one subnet for work devices (e.g. 192.168.10.0/25)
• Use another for guests or IoT devices (e.g. 192.168.10.128/25)
• Create isolation to prevent a hacked smart lightbulb from reaching work files

4. Airport Free Wi-Fi

Ever connected to airport Wi-Fi? You’re likely on a very large shared LAN.

Airport IT splits users into dynamic subnets to reduce congestion and limit interaction between travelers. You and a stranger might be on different subnets, even if connected to the same Wi-Fi.

This keeps things organized — and reduces security risks.

These examples show that subnetting isn’t some abstract tech concept. It’s happening around you every day, quietly keeping your digital life faster, safer, and more organized.

Final Thoughts

Subnetting might sound intimidating at first, but at its core, it’s just a smart way to organize networks. Whether you're at home, in the office, or connected to a large-scale network at school or the airport — subnetting helps keep things running smoothly.

It controls how devices communicate, saves valuable IP space, reduces traffic overload, and adds a layer of organization that’s essential in today’s connected world.

Once you understand how IP addresses are divided into networks and hosts, subnetting becomes much easier to visualize — and much more powerful to use.

Key Takeaways

• Subnetting means dividing a large network into smaller, manageable sub-networks.
• It helps reduce congestion, improve performance, and organize devices more efficiently.
• Every IP address is split into a network part and a host part, determined by the subnet mask.
• The subnet mask acts like a filter, showing which portion of the IP address belongs to the network.
• Broadcast addresses (ending in .255) are used to send messages to all devices in a local network.
• CIDR notation (like /24) tells us how many bits are reserved for the network portion of the address. The remaining bits define how many devices (hosts) can exist in the subnet.
• Subnetting helps prevent waste of private IPs — especially important in IPv4 networks.
• Real-world subnetting happens in homes, offices, campuses, public Wi-Fi, and more.
• You can check your current IP and subnet mask to understand how many devices your network supports.