Which statement best describes the primary function of a firewall?

• A. It blocks all traffic by default
• B. It controls traffic based on security rules
• C. It encrypts all communications
• D. It ensures only trusted traffic passes through

Answer: (B)

Firewalls enforce access control by applying security rules to traffic between networks or hosts. They inspect packets and connections and decide whether to permit or block based on criteria such as source and destination IPs, ports, protocols, and the connection state. This rule-based filtering is the core function, determining what is allowed to pass and what is blocked. Encryption handles confidentiality and is not the firewall’s job, and while many setups aim to permit only trusted traffic, the precise mechanism is the policy encoded in the rules, not a blanket notion of trust. Stateful firewalls enhance accuracy by keeping track of connection states, so they can differentiate new connections from ongoing ones and apply decisions accordingly.