What does a host-based firewall primarily do?

A host-based firewall primarily functions to control and regulate incoming and outgoing network traffic based on predetermined security rules set by the user or system administrator. The core purpose of a host-based firewall is to protect a single host (like a computer or server) from unauthorized access and potential attacks from the network.

The correct answer pertains specifically to the ability of a host-based firewall to disable certain communication ports, thus enhancing security by restricting access. For instance, by disabling all web-server ports except 443 (the default port for HTTPS traffic), the firewall can effectively mitigate risks associated with other web services that may be running on different ports. This is a practical and direct application of the capabilities of a host-based firewall.

In contrast, the other choices represent functionalities that go beyond the scope of a host-based firewall. Monitoring network traffic for anomalies is typically a function of intrusion detection systems. Encrypting data during transmission involves protocols like TLS/SSL, rather than the direct functionality of a firewall. Providing VPN access for remote users is a capability generally associated with different network devices or services specifically designed for creating secure connections, which is not the primary role of a host-based firewall.