What function does a firewall serve in a network?

A firewall plays a crucial role in network security by filtering incoming and outgoing traffic. This function is essential for protecting the internal network from unauthorized access and potential threats that could come from external sources. By implementing a set of predetermined security rules, a firewall can analyze data packets and determine whether to allow or block them based on their source, destination, or content. This capability helps prevent cyber attacks and unauthorized data breaches while allowing legitimate traffic to pass through.

In contrast to the other options, the primary focus of a firewall is not to connect devices, modulate signals, or broadcast data. Connecting devices pertains more to network switches and routers, which facilitate communication between different endpoints. Modulating signals is a function typically associated with telecommunications equipment, converting signals to enable long-distance transmission. Broadcasting data to all devices refers to how certain network configurations allow information to be sent to multiple recipients at once, which falls outside the security functions provided by a firewall. Thus, the filtering of traffic is the fundamental role that ensures the integrity, confidentiality, and availability of network resources.