Certified Information Systems Security Professional (CISSP) Practice Exam

A firewall plays a critical role in network security by monitoring and controlling incoming and outgoing network traffic based on predetermined security rules. The correct response highlights the function of filtering traffic at the network and transport layers (layers 3 and 4) of the OSI model. By examining the headers of packets, a firewall makes decisions about whether to allow or block specific traffic based on factors such as IP addresses, port numbers, and protocols. This filtering capability helps in protecting the network from unauthorized access and potential threats, ensuring that only legitimate traffic is permitted.

The other options do not accurately represent the primary function of a firewall. Enhancing data transfer speed refers to performance optimization rather than security, which is not a goal of firewalls. Storing data securely pertains to data storage or encryption technologies, while providing wireless connectivity relates to networking infrastructure rather than the firewall’s purpose. Thus, the filtering of traffic at the specified layers makes the correct answer integral to a firewall's function in safeguarding a network.