What is the primary function of a sniffer?

The primary function of a sniffer is to capture and display network packets that traverse a network. This capability allows network administrators and security professionals to monitor network traffic in real-time, analyzing the data packets to troubleshoot issues, inspect for unauthorized access, and detect anomalies that may indicate security breaches.

By capturing packets, sniffers provide insights into the data being transmitted across the network, including source and destination addresses, protocols in use, and the actual content of the data (as long as it's not encrypted). This function is crucial for understanding how the network is operating and for maintaining its security integrity.

The other options represent different functionalities that do not align with the primary role of a sniffer. For instance, while a firewall provides a barrier to protect a network, it does not capture data packets like a sniffer does. Similarly, a device that generates network traffic is concerned with creating data flows rather than analyzing them, and a tool for cleaning up malicious software focuses on remediation rather than monitoring and capturing data.