Firewall

Firewalls are special-purpose network equipment. They pass network traffic in a similar way to routers or switches.

Real-Life Concept
A firewall is very similar to a router in that it passes network traffic and can be configured with specialized routing rules. However, a firewall usually sits at the boundary of a network between the other computers and the Internet. The firewall has a security focus and may incorporate additional scanning and detection technologies to block malicious traffic.