Which of the following firewalls inspects the actual contents of packets?

Application-level firewalls, also called proxy firewalls or application layer gateways, operate at OSI Layer 7 and fully reconstruct application-layer sessions to inspect payload contents including HTTP request bodies, URLs, commands, and data. Because they act as a full proxy between client and server, they can detect malicious content, protocol anomalies, and policy violations embedded within the packet payload. This deep content inspection is what distinguishes them from stateful inspection and packet filtering firewalls.

Packet filtering firewalls examine only Layer 3 and Layer 4 header fields such as IP addresses and port numbers, and do not read or analyze the actual payload of packets.

Stateful inspection firewalls track connection state and session context across packets, but they do not perform application-layer content inspection of the packet payload.

Circuit-level firewalls monitor TCP handshake validity at the session layer to verify that connections are legitimate, without inspecting the actual content or data carried within those connections.