Describe the function of a firewall.

A firewall serves a crucial role in network security by controlling the flow of incoming and outgoing traffic based on established security rules. It acts as a barrier between a trusted internal network and untrusted external networks, such as the internet. By examining data packets that attempt to enter or leave the network, the firewall can permit or block traffic based on predefined security criteria, which may include source and destination IP addresses, ports, and protocols.

This functionality helps protect systems from unauthorized access, attacks, and intrusions, thus ensuring that only legitimate traffic can pass through. In doing so, it prevents potential threats, such as malware or unauthorized access attempts, from compromising the network's integrity and confidential information. The controlled access provided by a firewall is essential for maintaining a secure network environment. This defined role distinguishes it from other options, as it is specifically about managing traffic with respect to security rather than functionality like boosting speed or data backup.