What is the primary function of a firewall?

The primary function of a firewall is to control incoming and outgoing network traffic. This is achieved by defining rules that determine which data packets are allowed to pass through the network boundary. Firewalls serve as a barrier between trusted internal networks and untrusted external networks, such as the internet. By controlling traffic, firewalls help to protect systems from unauthorized access, cyber attacks, and other security threats.

Firewalls can operate at various levels of a network, including network-layer firewalls that inspect traffic based on IP addresses and ports, as well as application-layer firewalls that filter traffic based on specific application protocols. They can also provide logging and reporting capabilities, allowing administrators to monitor for suspicious activities.

While managing user permissions, monitoring system performance, and encrypting data are important security functions, they do not align with the primary role of firewalls, which is focused on traffic management and protection between network segments. This is why the option regarding controlling network traffic is the most appropriate answer.