What is the primary function of a firewall in a layered security architecture?

• A. To block all traffic
• B. To encrypt all data end-to-end
• C. To store security logs only
• D. To control and filter traffic between networks or segments based on configured rules

Answer: (D)

Firewalls act as gatekeepers between networks, enforcing access control by filtering traffic according to defined rules. In a layered security setup, they sit at network boundaries or between segments to block or allow traffic, limiting unauthorized access and restricting lateral movement. They inspect traffic using criteria like source and destination IPs, ports, protocols, and direction, and many modern firewalls track connection state to ensure traffic belongs to legitimate sessions. This rule-based filtering is the primary function; encrypting data end-to-end is handled by encryption technologies, and storing logs is a useful capability but not the main purpose. Firewalls support defense in depth by enforcing policies and helping contain threats within segments.