Simplifying the Sh*t Out of Subnetting…From Someone Who HATES Math

I’m really, really curious…and I ask far too many questions. But that has served me very well. So well, in fact, that I actually understand subnetting.

When I first came into the cyber profession, I wondered why learning subnetting was so difficult. I’m a cybersecurity GRC and Policy Analyst, social worker, HR specialist and certified hypnotist. I had no history of subnetting and was disinterested in a present of future where subnetting play any kind of role.

But what I do, is create content and simplify concepts.

As an experienced Instructional Designer (ID), I know that being a Subject Matter Expert (SME) is not a requirement to create meaningful learning experiences.

The real expertise lies in understanding how to help others remember how to learn. I had a SME handy, but I wanted to understand subnetting myself because, well, I’m in cybersecurity. So, I set a goal to understand subnetting to make my course design, conversations and GRC work more informed and useful.

It’s been three years since I set that goal, and here we are.

What I Immediately Noticed About Subnetting Training

#1 Training Materials Were Not Made for Me.

Reading the training materials and listening to subnetting videos was like eavesdropping on a conversation that had nothing to do with me. It felt like they were speaking a different language. The content didn’t relate to anything I was doing. If anything was relevant to my needs, goals, or interests as a cybersecurity professional, it was purely by accident. It was like trying to learn from a conversation where they forgot I was in the room.

#2 Nobody Knows What a “Bit” Is.

I must have asked 325 people to help me understand what a bit is, and all I got was “1s and 0s” or some other symbolic explanation that didn’t get me anywhere. I wanted to know what a bit is in real life. Like, in reality, what’s happening in the computer that I can point to and say, “Look, a bit!” It was as if everyone knew the concept, but nobody could show me what it looked like in action.

#3 IP Addressing is Taught Ass Backwards.

We should start with Public IPs! I mean, there’s no internet communication without Public IPs, but here we are spending hours and hours subnetting private IP addresses like it’s some kind of Muni Long song that never ends. It’s just nonsensical to start from the inside out when the whole point of IP addressing is communication across networks.

Why Standard Subnetting Training Didn’t Help Me

Typical training is less than helpful when you’re too curious. As mentioned previously, I ask too many questions that may seem unrelated to the topic and folks get frustrated with me. I get it.

Eventually, I did my own research and discovered that…

Damn, this stuff is hard. I mean, I’m not a lover of numbers. I prefer words, colors, and spaces. Numbers give me the heebie-jeebies. But here’s what I figured out…

Understanding the Basics: Networks Address, IP Address, Bits, Subnetting, and Memory

Network address vs. IP address

The network address is different from an IP address assigned to a device; it serves as the identifier for an entire network rather than an individual device.

The network address, like 192.168.1.0 in a 192.168.1.0/24 subnet, is never assigned to any specific device because it represents the location of the network itself — the starting point or the "lot number" of a house. THe IP address doesn’t come into play until hosts (devices) are added to the network.

An IP address is not an address…it’s directions!

An IP address is not just a single identifier; it’s a set of directions that help data navigate to the correct network. Once the data reaches the right network, the MAC address (a unique identifier built into each network interface card) is what actually identifies a specific device.

In essence, the IP address is about finding the right network, while the MAC address is about finding the specific device on that network.

What is a Bit, Really?

A bit is an electrical pulse. It’s the smallest unit of data in computing, stored physically in memory cells made up of transistors. These transistors switch on or off to represent the binary data (1s and 0s). When you think about a bit, think about it like an actual physical state — an electrical pulse or no pulse, a tiny switch flipping open or closed inside your device. It’s physical, just like memory, and it’s the building block for everything in computing, including subnetting.

Borrowing Bits in Subnetting

Subnetting is about dividing space differently. It initially may have been divided into halves, now I want to divide it into 4ths.

When we borrow bits, we just turn the most significant bit in the host from “off” to “on”.

When you borrow bits, you’re taking some of the bits that were originally designated for hosts (devices) and using them to create more networks (subnets).

This whole process is managed by software, like your router’s operating system or firmware. The software reallocates bits between the network and host portions of IP addresses, updates the subnet mask, and tells devices how to interpret these changes. So, you’re not physically changing anything — you’re giving new instructions to the software that manages your network.

So, What’s Really Happening in Subnetting?

(Reference RFC 791: Internet Protocol)

Before Subnetting:

You have a single, big network — one big “broadcast domain” where every device hears every other device’s broadcast traffic. It’s either noisy, crowded, and not very efficient OR it’s a waste of space because it’s underutilized.

For instance, before the Louisiana Purchase in 1803, the territory of Louisiana was a huge region claimed by France. It stretched from the Mississippi River in the east to the Rocky Mountains in the west, and from the Gulf of Mexico in the south to the Canadian border in the north. This enormous area covered approximately 828,000 square miles, more than doubling the size of the United States at the time.

The land included within the original Louisiana Territory now includes all or parts of 15 current U.S. states:

Louisiana (includes only a small portion of the original territory), Arkansas, Missouri, Iowa, Minnesota (west of the Mississippi River), North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, Montana, Wyoming, Colorado, New Mexico (partially) & Texas (partially, specifically the area around the Red River).

Think of Louisiana as it used to be as the way the old IP addressing system worked.

Scale and Scope:

Louisiana before the purchase was a very large and resource-rich area inhabited by diverse indigenous nations and communities with their own established systems of governance, culture, and resource management.

However, from the perspective of the people and governments who claimed the territory, it was seen as unstructured and uncharted.

Class A Network

A Class A network in traditional IP addressing provided a massive address space, capable of supporting over 16 million hosts.

That’s like giving every single person in New York City, Los Angeles, and Chicago combined — which is about 15.2 million people — their own apartment building, even though most people only need a single apartment.

OH, and each apartment building is 1.6 million stories high!!!

It’s far more space than most organizations could ever use, leading to significant waste and inefficiency.

Just as the Louisiana Territory was perceived as more than what could be effectively managed or used under the administration at that time, Class A networks often had far more resources allocated than were actually needed.

Subdivision and Administration:

After the Louisiana Purchase, the territory was divided into smaller administrative regions, eventually forming new states to better manage the land and resources.

However, even after this subdivision, the size and the complex, diverse cultures and communities already existing in these areas posed significant challenges for the colonizers…I mean “new administration”. Many regions remained sparsely populated by settlers, and the allocation of land did not account for the indigenous peoples who had lived there for generations.

The introduction of Class B and C networks aimed to distribute the address space more effectively. However, these subdivisions were still inefficient and wasteful. For example, a Class B network could allocate up to 65,534 IP addresses to an organization that only needed a few thousand, leaving a significant number of addresses unused.

This inefficiency is similar to the early days of the Louisiana Territory’s subdivision, where resources were not fully utilized despite the creation of smaller states, and the needs and rights of existing communities were overlooked.

After Subnetting:

You’ve essentially told the router,

“Listen up! We need you to understand that there are now multiple smaller networks within this larger network (LAN), so you need to know how to correctly route packets to these new destinations .”

When you create subnets using Classless Inter-Domain Routing (CIDR), the router’s job is to use the updated subnet masks and routing tables to correctly direct packets to the appropriate subnet. CIDR, established by RFC 1519 in 1993, allows for more flexible and efficient allocation of IP addresses compared to the traditional classful addressing system. The router now recognizes multiple “new locations” or subnets within the LAN and knows how to route packets to the specific subnet they belong to, rather than broadcasting them across the entire network.

SBy dividing the network into smaller, more manageable subnets, you’ve created multiple broadcast domains. Each subnet has its own range of addresses and limits broadcast traffic to only the devices within that subnet.

The router, guided by the updated CIDR-based subnet masks and routing information, now efficiently routes packets to their designated subnet, reducing unnecessary traffic and improving the overall performance and organization of the network.

The Router’s Role: The Software and the Hardware

Inside your router, the software — yes, it’s software! — handles these changes. It updates routing tables, performs bitwise calculations, and keeps everything moving. But there’s also hardware involved, like the Network Interface Card (NIC). The NIC helps in physically transmitting and receiving data packets, but it relies on the instructions given by the software.

Your router’s software does the thinking: it recalculates, routes, and prioritizes traffic, while the NIC does the talking — sending packets in and out based on the routing decisions.

Subnetting and the OSI Model: Where Does It Fit?

Subnetting mainly lives at the Network Layer (Layer 3) of the OSI model. That’s where IP addresses and routing happen. Routers operate at this layer, using subnet masks to figure out how to send packets to their correct destinations.

While subnetting is a Layer 3 concept, it can also impact Layer 2 (Data Link Layer) because switches use MAC addresses to forward traffic efficiently based on the subnet divisions. And when you clean up network traffic with subnetting, you make life easier for Layer 4 (Transport Layer) protocols like TCP and UDP, which can deliver data more reliably and quickly.

What I Finally Figured Out

Subnetting isn’t about memorizing charts or doing math for the sake of it. It’s about understanding how networks talk to each other and how you can control that conversation to make your network safer, faster, and more efficient.

Subnetting helps reduce traffic, improves performance, and enhances security by creating smaller, isolated networks. And it does all this without changing a thing on your motherboard — it’s all in the software, all instructions, all logical.

So, if you’re like me and found subnetting confusing because it felt like learning a language without context, just remember: it’s all about how you direct the flow of information.

And the key players are the bits, the software doing the calculations, and the routers and switches making those decisions come to life.

Check Out My Mural!

I put together a Mural packed with insights about what a bit really is (it’s physical, just like memory) and why I describe IP addressing as infrastructure that belongs to connections, not just to you or your laptop. Take a look, and if you have questions or comments, feel free to ask.

I’ve just created a substack and I would love it if you’d join me over there and SUBSCRIBE! https://cherylabram.substack.com/