In network sniffing, what type of data is primarily captured?

In network sniffing, the primary focus is on capturing data packets transmitted over the network. Data packets are the fundamental units of data that are sent over a network and contain both header information (such as source and destination IP addresses) and the actual payload data (the content being transmitted).

When a network sniffer operates, it intercepts these packets as they travel through the network cables or wireless signals. This allows analysts to monitor network traffic for various purposes such as troubleshooting, performance monitoring, or detecting malicious activities. The packets can provide a wealth of information, including protocol details, communication sessions, and any transferred data.

Other options, while they may be related to network analysis, do not represent the primary focus of data captured during sniffing. File sizes can be part of the payload found within packets but are not the main data captured. Subnet information and IP addresses are crucial for understanding the network layout and routing but are just part of the packet header information, not the primary data being focused on. Thus, the correct answer highlights the essential concept of packet capture in the realm of network sniffing.