A stateful packet inspection firewall logs the following items:
- What happened with the connection (e.g., allowed or denied)
- The source IP
- The destination IP
However, the content of the traffic is not commonly captured by stateful packet inspection firewall logs. Stateful firewalls track the state of active connections and make decisions based on the state of those connections, but they do not inspect the actual content of the packets beyond header information. Content inspection is typically done by deep packet inspection (DPI) firewalls or intrusion detection/prevention systems.
Therefore, the correct answer is: The content of the traffic.