Which device inspects and controls traffic trying to enter or leave a network boundary?

• A. NAT
• B. Load Balancer
• C. Firewalls
• D. VPN Gateway

Answer: (C)

Firewalls sit at the network boundary and inspect traffic crossing into or out of the network, applying rules that determine whether to allow or block it. They examine factors like where the traffic is coming from, where it’s going, what port and protocol it uses, and the state of the connection, to enforce security policies. Modern firewalls can also perform deeper inspection and threat prevention, making them effective at preventing unwanted access while permitting legitimate communication. NAT translates addresses, which is about mapping internal addresses to external ones rather than enforcing access control. A load balancer focuses on distributing traffic and optimizing performance, not primarily on filtering at the boundary. A VPN gateway handles encrypted tunnels for remote access, not general traffic filtering at the network edge. This boundary-inspecting and policy-enforcing role is what makes a firewall the device that controls traffic entering or leaving a network.