What is a network security system that monitors and controls incoming and outgoing network traffic based on security rules called?

A network security system that monitors and controls incoming and outgoing network traffic based on security rules is called a firewall. This system acts as a barrier between trusted and untrusted networks, ensuring that only authorized traffic is allowed to pass through based on predefined security protocols.

Firewalls can operate at various levels of a network and can be implemented in software, hardware, or both. By establishing rules that allow or deny traffic, they protect internal networks from unauthorized access and various cyber threats.

Other options such as an Intrusion Detection System focus primarily on detecting and reporting unauthorized access attempts rather than controlling traffic. A Virtual Private Network provides a secure connection over the internet but does not monitor traffic in the same way a firewall does. A Proxy Server acts as an intermediary for requests from clients seeking resources from other servers, but it does not specifically enforce security rules beyond managing requests. Thus, the functionality of a firewall in controlling network traffic clearly distinguishes it from these other network security components.