What role does a firewall play in network security?

A firewall plays a critical role in network security primarily by controlling incoming and outgoing network traffic. It acts as a barrier between trusted internal networks and untrusted external networks, such as the internet, helping to prevent unauthorized access and attacks. Firewalls enforce predetermined security rules, allowing or denying traffic based on the IP addresses, ports, and protocols specified in these rules.

This traffic control is essential for protecting sensitive data and ensuring that only legitimate communications occur within the network. By filtering traffic, firewalls help mitigate various threats like intrusion attempts, malware, and denial-of-service attacks, thus maintaining the integrity and security of the network.

The other roles mentioned in the options, such as encrypting confidential data, monitoring user activity, and tracking data integrity, are handled by different types of security solutions and tools, but they are not the core functions of a firewall.