What is the main function of a firewall?

The main function of a firewall is to control incoming and outgoing network traffic, which involves enforcing a set of security rules to determine what data packets are allowed through and which are blocked. Firewalls create a barrier between a trusted internal network and untrusted external networks, such as the internet.

By filtering traffic based on predefined security criteria, firewalls protect networks from unauthorized access, attacks, and malicious traffic. They can operate at different levels of the network stack, providing capabilities like packet filtering, stateful inspection, and even application-level gateways, depending on the sophistication of the firewall technology being used.

Understanding this fundamental role helps emphasize that firewalls do not simply aim to prevent all traffic (as that would disrupt legitimate use) or monitor performance (which is a separate function), and while they may have an indirect effect on network speed by managing traffic flow, that is not their primary purpose. The control of traffic is essential for maintaining security and ensuring that users can safely access network resources.