What is the main function of a network sniffer?

The primary function of a network sniffer is to capture and analyze network communication. This tool intercepts data packets as they travel across a network, allowing administrators or security professionals to monitor traffic for troubleshooting, performance analysis, or security assessments. By analyzing this data, one can identify issues such as network congestion, unauthorized access attempts, or potential vulnerabilities within the network infrastructure.

Network sniffers operate by placing the network interface card (NIC) into promiscuous mode, enabling it to read all data packets on the network segment it is connected to, rather than just those specifically addressed to it. This capability is crucial for diagnosing problems, ensuring compliance with policies, and optimizing performance by understanding how data flows through the network.

The other options present functions that do not accurately represent what a network sniffer is designed to do. For instance, recording user activity and transmitting it to the server relates more to monitoring tools rather than the direct analysis of network traffic. Protecting workstations from intrusions refers to security mechanisms like firewalls and antivirus software. Cataloging network data to create a secure index does not align with the fundamental purpose of a network sniffer, as this implies a structured approach to organizing data rather than the immediate capture and examination of traffic.