Glossary

Firewall

A filter that decides which network traffic is allowed in or out, based on rules.

Definition

A firewall enforces a security policy on a network boundary. It might be a feature in your operating system, a function of your router, or a dedicated appliance for a corporate network. Rules typically match on source/destination IP, port, and protocol, and either allow or drop the traffic.

Stateful firewalls track active connections; application-layer firewalls (sometimes called next-gen firewalls) inspect contents to detect threats. Default-deny rules — block everything except what you explicitly allow — are the strongest posture.

Example

Your home router's firewall blocks inbound connections from the public internet by default, so a scanner sweeping IPs can't directly reach the laptop sitting on your living-room desk.

Frequently asked questions

Do I need a firewall if I use a VPN?

Yes — a VPN encrypts traffic but doesn't filter it. A firewall is a separate control.

Will a firewall block malware?

It can block the network traffic malware uses, but not the malware on your device. You still need updates and antivirus.

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