Which of the following best describes a firewall?

A firewall is best described as a device that monitors network traffic. Its primary function is to filter incoming and outgoing data packets based on predefined security rules, allowing or blocking traffic as necessary. This monitoring capability is crucial for protecting networks from unauthorized access and cyber threats, ensuring that only legitimate traffic is permitted to flow through the network.

In practice, firewalls can be implemented through hardware, software, or a combination of both. They track connections and enforce security policies, helping to maintain the integrity and security of a network by inspecting data packets and determining whether they should be allowed to pass based on specified criteria, such as source and destination IP addresses, protocols, and ports.

The other options, while related to network functions, do not accurately describe the primary role of a firewall. For instance, a device that forwards packets typically refers to routers or other network devices that direct traffic but do not provide the same level of security monitoring. A device that encrypts data is related to information security but does not involve monitoring network traffic for threats. Lastly, a device that increases bandwidth speaks to performance enhancements rather than security functions like those performed by firewalls.