IP Addressing and Subnetting: Beginner’s Guide

If you’re learning networking, IP addressing and subnetting are two concepts you need to understand.

Every device communicating on an IPv4 network uses an IP address, while subnetting allows network administrators to divide larger networks into smaller networks.

These concepts are used everywhere in IT:

• Local networks
• Servers
• Routers
• Firewalls
• Cloud environments
• VPNs
• Enterprise networks
• Cybersecurity

In this guide, we’ll start from the basics and gradually understand how IP addresses and subnetting work.

What Is an IP Address?

An IP address is a logical address used to identify a device on an IP network.

An IPv4 address consists of 32 bits divided into four octets.

For example:

192.168.1.10

Each octet can have a value from:

0 → 255

So an IPv4 address contains four numbers:

192 . 168 . 1 . 10
 ↑     ↑    ↑    ↑
Octet Octet Octet Octet

IPv4 Address Structure

An IPv4 address contains two main parts:

Network portion + Host portion

For example:

192.168.1.10/24

With a /24 network:

Network: 192.168.1
Host:    10

The subnet mask tells the device which part represents the network.

What Is a Subnet Mask?

A subnet mask determines the network and host portions of an IPv4 address.

A common example is:

255.255.255.0

This corresponds to:

/24

So:

192.168.1.10/24

means:

Network: 192.168.1.0
Host:    10

CIDR Notation

Instead of writing the complete subnet mask, we can use CIDR notation.

For example:

192.168.1.10/24

The /24 means that the first 24 bits are used for the network portion.

Some common CIDR values are:

*For typical IPv4 subnets, excluding the network and broadcast addresses.

What Is a Network Address?

The network address identifies the network itself.

For example:

192.168.1.0/24

The network address is:

192.168.1.0

You don’t normally assign the network address to a regular host.

What Is a Broadcast Address?

The broadcast address is used to communicate with all hosts within a subnet.

For:

192.168.1.0/24

the broadcast address is:

192.168.1.255

So the typical usable host range is:

192.168.1.1
        ↓
192.168.1.254

Example: 192.168.1.0/24

Let’s look at the complete network:

Network Address:
192.168.1.0

First Usable:
192.168.1.1

Last Usable:
192.168.1.254

Broadcast:
192.168.1.255

That gives us:

254 usable host addresses.

Private IPv4 Addresses

Private IP addresses are commonly used inside local networks.

There are three main private IPv4 ranges:

10.0.0.0/8

10.0.0.0 → 10.255.255.255

172.16.0.0/12

172.16.0.0 → 172.31.255.255

192.168.0.0/16

192.168.0.0 → 192.168.255.255

For example:

192.168.1.10

is a private IP address.

Private addresses are commonly used inside homes and organizations.

Public IP Addresses

A public IP address is globally routable on the Internet.

Your organization may receive a public IP address from an Internet Service Provider.

A simplified network could look like:

Internal Network
192.168.1.0/24
       |
    Router
       |
Public IP
       |
   Internet

The router can use NAT to allow private devices to communicate with Internet services.

What Is Subnetting?

Subnetting means dividing a network into smaller networks.

Imagine you have:

192.168.1.0/24

Instead of using one network for everything, you could divide it into multiple smaller networks.

For example:

Network 1 → 192.168.1.0/26
Network 2 → 192.168.1.64/26
Network 3 → 192.168.1.128/26
Network 4 → 192.168.1.192/26

Each /26 network provides:

62 usable host addresses.

Why Do We Use Subnetting?

Subnetting provides several advantages.

1. Better organization

You can separate different departments.

Management
192.168.10.0/24

IT
192.168.20.0/24

HR
192.168.30.0/24

2. Smaller broadcast domains

Smaller networks can reduce broadcast traffic.

3. Better security

Network segmentation can make it easier to control communication between groups.

4. Efficient IP usage

You can allocate address space according to the number of devices actually needed.

Subnetting Example

Imagine an office needs four separate networks.

We start with:

192.168.1.0/24

We can divide it into four /26 networks.

Subnet 1

192.168.1.0/26

Usable:

192.168.1.1
-
192.168.1.62

Broadcast:

192.168.1.63

Subnet 2

192.168.1.64/26

Usable:

192.168.1.65
-
192.168.1.126

Broadcast:

192.168.1.127

Subnet 3

192.168.1.128/26

Usable:

192.168.1.129
-
192.168.1.190

Broadcast:

192.168.1.191

Subnet 4

192.168.1.192/26

Usable:

192.168.1.193
-
192.168.1.254

Broadcast:

192.168.1.255

Subnetting Cheat Sheet

Here’s a useful table to save for later:

The general formula for typical IPv4 subnets is:

Usable hosts = 2^host_bits - 2

For /26:

32 - 26 = 6 host bits

2^6 - 2
= 64 - 2
= 62 usable hosts

How to Calculate Subnets

A useful technique is the block size.

For example:

192.168.1.0/26

The subnet mask is:

255.255.255.192

Calculate:

256 - 192 = 64

Therefore, the networks increase by 64:

0
64
128
192

So the subnets are:

192.168.1.0/26
192.168.1.64/26
192.168.1.128/26
192.168.1.192/26

This technique becomes very useful when doing subnetting exercises.

How to Find the Subnet of an IP

Suppose you have:

IP:
192.168.1.70

Mask:
/26

The /26 networks are:

192.168.1.0
192.168.1.64
192.168.1.128
192.168.1.192

Since 70 falls between 64 and 127, the IP belongs to:

192.168.1.64/26

Therefore:

Network:
192.168.1.64

First Host:
192.168.1.65

Last Host:
192.168.1.126

Broadcast:
192.168.1.127

VLSM — Variable Length Subnet Masking

Once you understand basic subnetting, you can learn VLSM.

VLSM allows different subnet sizes to be used within the same overall address space.

For example:

IT Department
/26

HR Department
/27

Management
/28

Point-to-point link
/30

This can make IP allocation more efficient.

Subnetting in Real Networks

Subnetting is used everywhere in professional IT environments.

For example:

Company Network
       |
   Core Router
       |
 ┌─────┼─────┐
 ↓     ↓     ↓
IT    HR   Guest
/24   /25   /26

Organizations can combine subnetting with VLANs, routing, and firewall policies to create structured and secure networks.

Common Beginner Mistakes

Mistake 1 — Confusing network and host addresses

For:

192.168.1.0/24

192.168.1.0 is the network address, not normally a host address.

Mistake 2 — Forgetting the broadcast address

For /24:

.255

is the broadcast address.

Mistake 3 — Confusing /24 with 255.255.255.0

They represent the same subnet mask.

Mistake 4 — Forgetting that subnet sizes change

For example:

/24 → 254 usable hosts

/25 → 126

/26 → 62

/27 → 30

The number of available hosts decreases as the prefix becomes larger.

How to Practice Subnetting

The best way to learn subnetting is to practice.

Try solving these:

Exercise 1

192.168.10.25/24

Find:

• Network address
• First host
• Last host
• Broadcast

Exercise 2

192.168.10.130/26

Find:

• Network
• First host
• Last host
• Broadcast

Exercise 3

10.10.10.200/27

Find:

• Network
• First host
• Last host
• Broadcast

Don’t worry if these look difficult initially. Subnetting becomes much easier with repetition.

Useful Networking Commands

You can also examine IP configuration directly on your computer.

Windows

ipconfig

More detailed information:

ipconfig /all

Linux

ip addr

Routing table:

ip route

These commands are useful when troubleshooting IP configuration.

Conclusion

IP addressing and subnetting are fundamental networking skills.

You should understand:

• IPv4 addresses
• Subnet masks
• CIDR notation
• Network addresses
• Broadcast addresses
• Private IP addresses
• Public IP addresses
• Host ranges
• Subnetting
• VLSM

Don’t try to memorize every subnet immediately.

Practice calculating networks until the process becomes automatic.

Once you understand subnetting, you’ll be much better prepared for VLANs, routing, DHCP, firewalls, VPNs, and Cisco networking.

FAQ