Cybersecurity Foundations · 4 min
Firewalls
Rules that decide which traffic passes
This lesson explains the concept, then checks your understanding in a short interactive exercise.
What a firewall does
A firewall inspects traffic and allows or denies it based on a set of rules, typically using source, destination, port, and protocol.
- Inbound — traffic entering a network or host
- Outbound — traffic leaving a network or host
- Network firewall — protects a whole network segment
- Host firewall — protects a single device
What a firewall does NOT guarantee
A firewall is one control among many, not a complete defense.
- Allowed traffic is not automatically safe
- Denied traffic is not automatically malicious — it may just be misconfigured or unneeded
- A firewall doesn't inspect what's inside allowed traffic by default
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