What is NetFlow, or flow data?

NetFlow, and similar formats such as IPFIX and sFlow, are summaries of network connections that routers and switches can export: who talked to whom, on which ports, when, and how many bytes and packets. A flow record is like a phone bill: it lists calls, not what was said. Flow data is useful for capacity planning and for spotting unusual volumes or destinations, and it is cheaper to store than full traffic. It misses details such as DNS answers or the TLSTLS: Transport Layer Security. The encryption that protects most internet traffic, such as HTTPS. handshake. NetSenX reads its own copy of the traffic from an agent or a mirror port rather than relying only on exported flow records.

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