What is a Firewall?

Firewall

A firewall is a network security device or software that monitors and controls incoming and outgoing network traffic based on predetermined security rules.

It serves as a barrier between an internal, trusted network and external, untrusted networks (such as the internet), blocking unauthorised access while allowing legitimate communication to pass. Firewalls can be network-based (hardware) or host-based (software).

Modern firewalls often include additional features like intrusion detection, VPN support, and traffic filtering based on application behaviour.