NetFlow is a network protocol used by network devices such as routers and switches to collect IP traffic data and send it to a collector or analyzer for analysis. NetFlow provides detailed information about network traffic, including source and destination addresses, application protocols, and traffic volumes. By configuring NetFlow on the switch, the administrator can capture and analyze the traffic data to identify the source and destination addresses of the traffic causing the network slowness. This information can be used to optimize network performance and troubleshoot network issues.