What does a firewall do?

A firewall plays a critical role in network security by filtering incoming and outgoing traffic based on predetermined security rules. This means that it examines packets of data as they attempt to enter or leave the network and makes decisions on whether to allow or block that traffic based on established rules configured by network administrators.

By applying these security rules, firewalls can prevent unauthorized access to or from a private network, effectively protecting systems from cyber threats such as intrusions, malware, and other malicious attacks. The ability to monitor traffic helps in restricting access only to legitimate users and services, which is crucial for maintaining a secure network environment.

The other options provided, while relevant to data security and network management, do not accurately describe the primary function of a firewall. Encrypting data packets refers to securing data by encoding it, which is a separate technology related to data confidentiality. Generating backups of data is focused on data availability and recovery, unrelated to traffic management. Monitoring network performance is about assessing the efficiency and functionality of the network but does not define the traffic-control aspect of firewall operations.