Static packet filtering is sometimes used ________.

• A. Both A and B
• B. Border routers
• C. As a secondary filtering mechanism on an application proxy firewall
• D. Neither A nor B

Answer: (C)

Static packet filtering is a basic, stateless check of packet headers (like source and destination IPs, ports, and protocol) that can be performed very quickly but doesn’t consider connection state or content. Because of its simplicity, it’s best used as a lightweight, initial screen to discard obviously unwanted traffic before more intensive processing occurs.

In the context of an application proxy firewall, this fast filter can sit as a secondary step inside the firewall. It handles the easy wins upfront, reducing the load on the proxy, which then can perform its heavier, stateful, and application-layer inspections. This combination leverages the speed of static filtering while still relying on the proxy for deeper protection.

While static filtering can be implemented at border routers, using it as a secondary filter within an application proxy firewall aligns with the idea of conserving resources and layering defenses, which is why this placement is the most appropriate choice here.