Which statement best describes how firewalls handle traffic?

• A. They encrypt all traffic by default.
• B. They only monitor outbound traffic.
• C. They store copies of all network packets.
• D. All messages entering or leaving the network pass through the firewall and are examined, with those that do not meet security criteria blocked.

Answer: (D)

Firewalls act as a controlled gate between trusted and untrusted networks, evaluating each data packet against security rules. All messages entering or leaving the network pass through the firewall and are examined, and those that don't meet the criteria are blocked. This is how a firewall enforces access policies and protects against unwanted traffic from both directions. It’s not about encrypting traffic by default—that’s handled by encryption tools like VPNs; it doesn’t only monitor outbound traffic, since it checks traffic in both directions; and it doesn’t store copies of all packets—though it may log events, it doesn’t routinely archive every packet.