Which of the following types of firewall inspects only header information in network traffic?

Packet filter firewalls operate at the network layer and inspect only the header information of each packet - including source IP, destination IP, source port, destination port, and protocol. They apply static ACL-like rules to each packet independently without tracking session state or analyzing application-layer content. This makes them fast but less capable of detecting application-level threats.

Stateful inspection firewalls go beyond header inspection by tracking the state of active connections in a state table, allowing them to validate that packets belong to an established session.

Circuit-level gateway firewalls operate at the session layer and validate TCP handshake completion rather than simply checking header fields in isolation.

Application-level gateway firewalls (proxies) perform deep packet inspection at the application layer, examining payload content and application-specific commands, far beyond just header information.