During monitoring, what data sources would provide the most relevant information to investigate suspicious network activity?

Packet captures are indeed the most relevant source of information for investigating suspicious network activity. They provide a detailed view of the actual data being transmitted over the network, including headers, source and destination IP addresses, protocols, and the content of the packets themselves. This level of detail allows analysts to observe the flow of network traffic in real-time, identify unusual patterns, and analyze the behavior of specific connections.

For instance, packet captures can reveal if there is an unusually high volume of traffic from one source, indicating a potential Distributed Denial of Service (DDoS) attack, or help identify unauthorized communication with external servers, which could signify data exfiltration. Additionally, they help in reconstructing sessions to understand the sequence of events leading up to a security incident.

In contrast, application logs, system performance metrics, and database queries do provide useful information but may not offer the in-depth visibility into the network layer that packet captures do. Application logs can show errors or transactions occurring within software but may miss critical network anomalies. System performance metrics inform about CPU and memory usage but do not directly point to network activity. Database queries are essential for monitoring database operations but are limited to interactions with the database rather than the broader network context. Thus, while all these