Definition

It is a security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.

It acts as a barrier between trusted internal networks and untrusted external networks to prevent unauthorised access while allowing legitimate communication.

They can either be:

• Hardware-based physical devices or,
• Software-based programs running on a computer or server.

They filter traffic based on criteria like IP addresses, domain names, protocols, or ports and can block malicious data while allowing safe data to pass through.

Types of Firewalls

• Packet-filtering firewalls - they inspect packets of data and allow or blcok them based on user-defined rules.
• Stateful inspection firewalls - they monitor state of active connections and make decisions based on both the rules and the state of the connection.
• Proxy firewalls - they act as intermediaries, filtering traffic between the user and the destination.