What is the purpose of a firewall in network security?

A firewall serves to monitor and control incoming and outgoing network traffic, acting as a barrier between trusted internal networks and untrusted external networks. By applying predetermined security rules, firewalls help to prevent unauthorized access, protect sensitive data, and mitigate potential attacks from the outside, thereby maintaining the integrity and security of the network.

The primary function of a firewall is not to enhance network speed or efficiency, which is often an indirect benefit rather than a primary purpose. It also does not work to prevent data encryption, as encryption is crucial for securing data in transit. Additionally, firewalls do not automatically backup data; this is typically handled by separate backup systems or solutions that are specifically designed for data preservation. Thus, the correct answer emphasizes the crucial role of firewalls in managing and protecting network traffic.