Comprehensive and Detailed Explanation From Exact Extract:

Flow collectors differ from polling engines because they passively receive and process flow records sent by network devices, while polling engines actively poll devices for data (like SNMP). Devices must be explicitly configured to export their NetFlow, sFlow, or J-Flow records to the IP address and port of the flow collector, rather than being queried by the SolarWinds server.

The documentation states:

"To monitor flow data, devices must be configured to send their flow records to the collector. Unlike traditional polling, the collector does not initiate contact; it listens for incoming flow exports from network devices."