What is a network?

Before we attack or defend anything, we must understand how computers actually communicate. Networking is the human body that a security "doctor" needs to understand. This lesson gives you the mental model that everything else hangs on.

Almost every attack you'll ever learn about travels across a network. If networking is fuzzy for you, hacking will feel like magic. Get this clear now and the rest of the course opens up.

The simplest definition

A network is two or more computers connected together so they can share information. That's genuinely all it is. When your phone messages a friend's phone, when your laptop loads a website, or when you stream a film to your TV, computers are talking over a network.

You're already surrounded by them:

• Your home Wi-Fi is a small network joining your phone, laptop, and TV.
• Your workplace has a bigger one.
• All these smaller networks are joined into one gigantic global network we call the internet — literally an inter-network, a network of networks.

The post office picture

The easiest way to understand a network is a worldwide postal system — because it works almost exactly the same way.

[The internet is a postal system]

To send information to another computer, it's like posting a letter: it needs an address, it gets carried step by step, and it eventually arrives.

• Your devices (phone, laptop, TV) are the houses. Each can send and receive letters.
• Your router — the Wi-Fi box from your internet provider — is your local post office. Everything you send goes there first, and it forwards mail to the world and brings replies back.
• The internet is the worldwide delivery network — all the roads, sorting centres, and other post offices that carry your letter to any other house on Earth.

Wired vs wireless — same idea

Devices join a network in one of two ways:

• Wired — a physical Ethernet cable plugged into the router.
• Wireless — over Wi-Fi, radio waves in the air.

From the network's point of view it barely matters. One uses a physical road, the other uses radio waves, but both are just ways of carrying your "letters" to the local post office.

A first tour of the pieces

Names you'll keep meeting:

Don't memorise the table — just recognise the words when they appear.

LAN, WAN, and the sizes of networks

Networks come in different scales, and the vocabulary matters throughout this course:

• LAN (Local Area Network) — a network confined to one physical location: your home, an office floor, a single building. Your home Wi-Fi is a LAN.
• WAN (Wide Area Network) — a network spanning a much larger geographic area, connecting multiple LANs together — a company with offices in three cities connects them via a WAN. The internet itself is, in a sense, the largest WAN of all: a network of networks spanning the entire globe.
• MAN (Metropolitan Area Network) — a middle ground, typically covering a single city, less commonly referenced day-to-day but occasionally worth knowing exists.

This distinction matters practically in Path 12's network security material: attacks and defenses that make sense on a small, trusted LAN (like relying on physical proximity as a security control) often don't hold up once you're reasoning about a WAN spanning untrusted public internet infrastructure.

Bandwidth vs. latency — two different kinds of "speed"

Two terms people often conflate but which measure genuinely different things:

• Bandwidth — how much data can be transferred per unit of time (measured in Mbps/Gbps) — think of it as how wide the road is, how many cars can travel side by side at once.
• Latency — how long it takes a single piece of data to make the trip (measured in milliseconds) — think of it as how long the road is, regardless of how wide it is.

A connection can have high bandwidth but also high latency (a satellite internet connection, for instance, moves plenty of data per second but each individual round-trip takes noticeably longer due to the physical distance to space and back) — which is exactly why "my internet is fast" and "my connection feels laggy" can both be true statements about entirely different properties of the same connection. Path 02's later packets lesson and Path 12's Wireshark labs both give you direct, hands-on ways to actually measure this distinction yourself.

Why a security learner cares

Every message you send, every site you visit, and every attack a hacker launches is a "letter" travelling this postal system. Once you can picture the post office, you can reason about where an attacker might:

• Read a letter as it passes (eavesdropping)
• Forge the address on an envelope (spoofing)
• Impersonate a post office (rogue router / evil twin Wi-Fi)
• Block the delivery route (denial of service)

This mental model will serve you through the entire course.

In the post-office analogy, what real device plays the role of your "local post office"?

🧪 Lab — Peek at your own network

Do this on your own home network only.

1. On your phone or laptop, open your Wi-Fi settings and note the network name (SSID) and its security type (WPA2/WPA3 hopefully — we cover this in Path 12).
2. Try to find the IP address of your router. On Windows: ipconfig and look for "Default Gateway." On macOS/Linux: ip route | grep default.
3. Open a browser and type that IP address (usually 192.168.1.1 or 192.168.0.1). You'll see your router's admin login. Don't log in unless you know the password — but see, it's just a tiny web server sitting in your house.

Key terms

• Network — two or more connected computers sharing information.
• The internet — a global network of networks.
• Router — connects your home network to the internet and directs traffic.
• Client / server — the device asking vs the device providing.

Recap

• A network connects computers so they can share information.
• The internet is a "network of networks."
• The postal-system model: devices are houses, your router is the local post office, the internet is the global delivery network.
• Wired and wireless are just two ways to carry the same letters.

References

• How the Internet works — Mozilla MDN — an excellent beginner explainer.
• Cloudflare Learning: What is the Internet? — short and clear.
• Practical Networking: Fundamentals series — free deeper tutorials once you're ready.
• Networking Basics — Cisco

Next up → Routing basics