A firewall is a technical control that acts as a barrier between trusted internal networks and untrusted external networks, such as the Internet. It monitors and controls incoming and outgoing network traffic based on predetermined security rules. Firewalls can prevent unauthorized access, block malicious traffic, and enforce network security policies.

Access controls and encryption are also examples of technical controls, but they are not as specific to network resource protection as a firewall. Security awareness training is a managerial control focused on educating users about security best practices and policies.