Which device enforces security rules between networks?

• A. Router
• B. Firewall
• C. Switch
• D. Proxy

Answer: (B)

Enforcing security rules between networks means controlling what traffic is allowed to move from one network to another. A firewall is designed for this role. It sits at the boundary between networks (for example, between your internal network and the Internet or a DMZ) and applies security policies to each packet or session. It can block or allow traffic based on rules about IP addresses, ports, protocols, and even application data, and many firewalls track the state of connections to make smarter decisions.

A router’s main job is to determine the best path for packets to reach their destination, and while it can offer basic access control lists, that’s not its primary function. A switch connects devices within a local network and forwards frames, not enforce traffic rules between different networks. A proxy fetches resources on behalf of clients and can provide certain filtering at the application level, but it isn’t the device that generally enforces broad boundary security policies between networks.