Which term best describes a network security device that blocks unauthorized access while allowing outward communication?

• A. Antivirus software
• B. Intrusion detection system
• C. Access control list
• D. Firewall

Answer: (D)

The main idea is a device that sits at the network boundary and enforces which traffic is allowed to pass, blocking unauthorized access while permitting legitimate outward communication. This role is fulfilled by a firewall, which applies rules to incoming and outgoing traffic to protect the internal network while still enabling users and systems to reach external networks. Antivirus software protects individual devices from malware, not the network boundary. An intrusion detection system watches for suspicious activity and alerts or responds, but its primary function is detection, not enforcing broad access control. An access control list is a set of permissions used by devices to permit or deny specific traffic, but it’s a rule set rather than the boundary-enforcing device itself. A firewall embodies the protective boundary by enforcing these policies on traffic, enabling outward communication while blocking unauthorized access.