Afirewall is a system that filters network traffic. It can either let it pass or block it, according to some specified rules. For example, it can block incoming connections aimed at a certain port or outgoing connections to a certain IP address.

Firewalls can be as simple as a single piece of software, or more complex, like a dedicated machine whose only function is to act as a firewall.

See also

• Firewall (computing) on Wikipedia