Network Security Basics

Introduction

Networks carry everything: your passwords, files and video calls. Protecting them means controlling who can connect, what can talk to what, and whether traffic can be read in transit. This lesson is about defending networks you own or manage.

Firewalls

A firewall allows or blocks network traffic according to rules, like a guard at a gate.

A network firewall sits between networks, such as your home and the internet.
A host firewall runs on a single computer.
A sensible policy is default deny: block everything, then allow only what is needed.

Home routers include a firewall that blocks unsolicited incoming connections. Keep your router's software updated and change its default admin password.

Segmentation

Segmentation splits a network into zones, so a problem in one zone does not spread everywhere. For example:

Keep guest Wi-Fi separate from your main devices.
Put smart home gadgets, which are often poorly secured, on their own network.
In companies, separate servers, staff devices and public services.

If one device is compromised, the attacker cannot easily reach the rest.

Quick quiz

Why put smart home gadgets on a separate network from your computers?

Secure Wi-Fi

Use WPA3, or WPA2 with a strong passphrase, if WPA3 is not available. Do not use WEP or open networks for private use.
Use a long, unique Wi-Fi password and change the router's default admin login.
Disable features you do not use, and keep the router updated.

VPNs

A VPN (virtual private network) creates an encrypted tunnel between your device and a VPN server.

It protects traffic on untrusted networks such as public Wi-Fi.
It hides your traffic from your local network, but the VPN provider can see it, so choose a trustworthy one.
Companies use VPNs, and more and more zero trust approaches, to give staff secure access to internal systems.
A VPN does not make you anonymous or protect you from phishing and malware.

Common network attacks and defences

Attack	What it is	Defence
Eavesdropping	Reading unencrypted traffic	Use HTTPS, VPN and encrypted Wi-Fi
Man-in-the-middle	An attacker sits between you and a site	HTTPS with valid certificates, heed browser warnings
Denial of service	Flooding a service so it fails	Rate limiting, protective services, scalable design
Port scanning	Probing for open services	Firewalls, closing unused ports
Rogue Wi-Fi	A fake hotspot	Check the network name, use a VPN, avoid sensitive tasks

Monitoring

Good defence includes seeing what happens: logs from firewalls and servers, alerts for unusual activity, and a habit of reviewing them. You cannot respond to what you cannot see.

Try it yourself

Check your home network: change the router admin password, confirm Wi-Fi uses WPA2 or WPA3, update the router software and set up a guest network.

Summary

Firewalls use default-deny rules, and segmentation limits how far an attack can spread.
Strong Wi-Fi settings and VPNs protect traffic on the network.
Know the common attacks, use HTTPS everywhere, and monitor your logs.