Firewall

A firewall enforces rules that allow, block, or inspect network traffic crossing a defined boundary.

Format
Security & Encryption
Updated
Updated
Glossary Security & Encryption
Firewall Aliases: network firewall, host firewall.

Definition

A firewall enforces rules that allow, block, or inspect network traffic crossing a defined boundary.

How it works

Rules typically match traffic by source, destination, protocol, and port: let the world reach HTTPS, restrict SSH to your own addresses, drop the rest. Firewalls run on servers, network appliances, and cloud platforms alike. Keep the rules narrow and reviewed — a firewall controls who can knock on the door, not what happens if vulnerable software answers it.

Example: A server firewall might allow public HTTPS traffic while restricting administrative SSH access to known addresses.

Often confused: A firewall is one layer of defense; it does not patch software or replace authentication behind it.

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Sources

Last reviewed 2026-07-19.