What is Firewall?

A filter that controls which network connections are allowed in and out of your machine, your first line of defense against network attacks.

How it works

A default-deny firewall blocks everything you didn't explicitly allow, shrinking your exposed surface to near zero. On a desktop it's the highest-value five-minute hardening step, fronted by UFW on Ubuntu.

Example

In practiceYou deny all inbound by default and allow only SSH, so port scans find nothing open except the one service you run.

Do I need a firewall on a desktop?

Yes. Most compromises start with an exposed service. Default-deny inbound closes that door for the cost of one command.

Go deeper: Build a Hardened Linux Workstation

The complete, step-by-step guide — every command, config, and the reasoning behind it.

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