Which term describes a security device that filters traffic between networks?

• A. Intrusion Detection System
• B. Router
• C. Access Point
• D. Firewall

Answer: (D)

Filtering traffic between networks is the job of a firewall. A firewall sits at the boundary between networks and enforces security policies by inspecting each packet and deciding whether to allow or block it based on defined rules. It can operate at various layers, enforce access control, and often supports features like stateful inspection, network address translation, and VPN termination, making it the primary tool for controlling traffic flow between protected and untrusted networks.

Intrusion Detection System, on the other hand, focuses on noticing and reporting suspicious or malicious activity within traffic; it usually does not block traffic by itself and is often deployed in a monitoring role rather than as a gatekeeper. A router’s main purpose is to route packets along the best paths through a network, though it can apply simple access control lists, its core function is not filtering traffic as a security device. An access point provides wireless network access and security features related to wireless connectivity, not the broad traffic-filtering role between networks that a firewall performs.

So the term that best describes a security device that filters traffic between networks is firewall.