🌐 Understanding Subnetting: A Beginner's Guide with Simple Examples

In our previous blog, we explored the fundamentals of IP addresses—what they are, how they work, and the difference between IPv4 and IPv6. Now, it’s time to dive into a more advanced but extremely important concept in networking: Subnetting.

Subnetting might sound complex at first, but I promise, by the end of this post, you’ll be comfortable with what it is, why we use it, and how it works—with easy-to-understand examples.

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📘 What is Subnetting?

Subnetting is the process of dividing a large network into smaller, more manageable sub-networks (called subnets). Each subnet can function independently while still being part of the larger network.

Think of it like this: If a company owns a large office building, subnetting allows them to divide it into different departments—HR, Finance, IT—each with their own section and management, but still part of the same company.

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🎯 Why Do We Use Subnetting?

• ✅ Efficient IP Address Usage: Helps prevent wastage of IP addresses.

• ✅ Improved Network Performance: Reduces network congestion by limiting broadcast traffic to smaller subnetworks.

• ✅ Better Security & Management: Allows isolation of different departments or teams in an organization.

• ✅ Simplifies Troubleshooting: Easier to identify and isolate issues within a subnet.

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🧮 Before We Dive Deeper: A Quick Review of IP Addressing

Let’s recall an IPv4 address:

192.168.1.1

This address is made up of 32 bits, usually written in 4 decimal octets (each 8 bits):

Binary: 11000000.10101000.00000001.00000001
     =   192     . 168    .   1   .   1

In subnetting, we use something called a subnet mask to separate:

• The network portion of the address

• From the host portion (the devices)

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🛠 What is a Subnet Mask?

A subnet mask is used to determine how many bits are reserved for the network and how many are available for hosts.

Common subnet masks:

• 255.0.0.0 → /8

• 255.255.0.0 → /16

• 255.255.255.0 → /24

For example:

IP Address:     192.168.1.10
Subnet Mask:    255.255.255.0

This means:

• First 24 bits are for the network (/24)

• Last 8 bits are for hosts

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✂️ CIDR Notation

CIDR (Classless Inter-Domain Routing) uses a slash to represent how many bits are used for the network.

Example:
192.168.1.0/24 means the first 24 bits are network bits.

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🧠 Let’s Understand Subnetting with a Simple Example

🎯 Goal: Create 4 subnets from 192.168.1.0/24

/24 means:

• 256 total IP addresses (2⁸)

• 254 usable (1 for network, 1 for broadcast)

We want 4 subnets → 2 bits needed (2² = 4)

So we borrow 2 bits from host portion:

Subnet Mask: /26 (24 + 2)

Each subnet will have:

• 64 IP addresses (2⁶)

• 62 usable addresses per subnet

✅ Resulting Subnets:

👏 Now you’ve divided one large network into 4 smaller networks!

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🧾 How to Calculate Subnets (Step-by-Step)

1. Determine your original subnet (CIDR)
   e.g., /24 = 256 IPs

2. Decide how many subnets you want
   e.g., 4 subnets → Need 2 extra bits

3. Add bits to subnet mask
   /24 + 2 = /26

4. Calculate number of hosts per subnet
   2⁶ = 64 total addresses
   64 - 2 = 62 usable IPs

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📐 Quick Subnetting Cheat Sheet

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🧑‍🏫 Real-World Use Case

Let’s say you’re a network engineer for a small office:

• HR department needs 30 IPs

• IT needs 20 IPs

• Finance needs 10 IPs

You can subnet 192.168.1.0/24 into:

• /27 for HR (30 usable)

• /27 for IT (30 usable)

• /28 for Finance (14 usable)

This avoids wasting a full /24 subnet and keeps departments isolated!

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🔚 Conclusion

Subnetting is a key skill for anyone working in networking, system administration, or cloud infrastructure. It allows you to design more efficient, secure, and scalable networks.

Yes, it may seem math-heavy at first, but with a little practice, it becomes second nature. Start by experimenting with small subnet examples and using online tools to verify your answers.