Which firewall type is described as examining application messages in depth?

• A. Static packet filtering
• B. SPI
• C. Application proxy
• D. All of the above

Answer: (C)

Understanding at what layer a firewall inspects traffic and how deeply it looks into the data helps you pick the right type. Static packet filtering checks only header information like source/destination IPs and ports, making decisions without looking into the actual payload. Stateful packet inspection adds awareness of connection state, ensuring that packets belong to legitimate conversations, but it still centers on transport-layer data rather than decoding the application protocol. An application proxy, on the other hand, operates at the application layer and terminates the connection on behalf of the client and server, decoding the actual application messages (such as HTTP requests), analyzing them for protocol correctness and policy violations, and potentially blocking or altering content. Because it examines the application-layer messages in depth, this type is the best match for the description.