What is the function of a firewall in network security?

The function of a firewall in network security is primarily to control incoming and outgoing network traffic based on established security rules. Firewalls serve as a barrier between trusted internal networks and untrusted external networks, such as the internet. They inspect packets of data, filtering traffic to ensure that only authorized connections are allowed while blocking potential threats such as unauthorized access and malicious traffic. This is achieved through a variety of strategies, including stateful inspection, packet filtering, and proxy services, which ensure that the network's integrity and confidentiality are maintained.

In contrast to the other choices, which pertain to different aspects of network management or security, the specific role of a firewall is distinct and vital for protecting against unauthorized access and cyber threats. Backing up data relates to data preservation rather than traffic management, managing user access is more about authentication and authorization, and encrypting data is focused on confidentiality of content rather than controlling traffic flow. Hence, the accurate description of a firewall's purpose is its role in regulating data flow based on security protocols.