In computing, a firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.

There are mainly three types of firewalls, such as software firewalls, hardware firewalls, or both, depending on their structure. Each type of firewall has different functionality but the same purpose. ... Packet-filtering Firewalls. Circuit-level Gateways. Application-level Gateways (Proxy Firewalls)