Subnetting has a reputation for being one of the most confusing topics in networking — but that’s usually because people jump straight into the math without understanding the ideas underneath it. In Mapped Learning, we do things differently. Before we calculate anything, we build the mental tools that make subnetting make sense.
Today’s lesson is IPv4 Subnetting, Part 1, and it focuses entirely on the foundations:
What CIDR notation really means
How subnet masks are built
What “borrowing bits” actually does
How devices determine their network using AND‑ing
These concepts are the backbone of every subnetting problem you’ll ever solve.
⭐ Why start here?
Subnetting isn’t just a math exercise — it’s a way of thinking about networks. If you understand why subnetting works, the calculations become predictable instead of intimidating.
This lesson gives you that foundation.
We slow down, look at the structure of IPv4 addresses, and build the intuition you need before touching formulas or tables.
By the end of Part 1, you’ll understand:
CIDR Notation
How the /24, /25, /28, etc., define the boundary between network bits and host bits — and how that boundary shapes the entire network.
Borrowing Bits
How subnetting creates more networks by shifting bits from the host side to the network side, and why that changes the number of available hosts.
Binary Masks
How subnet masks look in binary, and how that binary pattern defines the network.
AND‑ing
How devices determine whether two IP addresses are on the same network by performing a simple logical operation.
These aren’t tricks — they’re the rules that every router and host follows.
⭐ What’s inside the lesson
In the video and slides, we walk through:
A clear explanation of CIDR notation
A breakdown of the CIDR acronym
A visual demonstration of borrowing bits
Binary subnet masks and what they represent
A real AND‑ing example showing two devices on different networks
Everything is designed to be simple, visual, and calm — the mapped‑learning way.
If you’re new to networking, this will make subnetting feel far less mysterious.
If you’re experienced, this will reinforce the fundamentals that make advanced topics easier.
⭐ What’s coming next
In IPv4 Subnetting, Part 2, we’ll take these concepts and turn them into practical skills:
The subnet mask table
The “magic number”
How to calculate networks quickly
Practice exercises to build confidence
Part 1 gives you the understanding.
Part 2 gives you the speed.
⭐ Thanks for being here
Everything I make is free, and it’s built to help you learn clearly and without noise. If this lesson helped you, share it with someone who’s learning too — it makes a real difference.
See you in Part 2.
Subnetting Part 1 slides with notes:
⭐ Watch the lesson (IPv4)
🎥 YouTube Video:
📝 Slides + Notes for IPv4:
