NetFlow is an embedded feature within Cisco^® IOS Software that records network traffic into the device cache to provide extremely granular and accurate traffic measurements. Because network traffic has a flow nature to it, the NetFlow accounting data that is built in the cache, characterizes the IP traffic being forwarded.

Exported NetFlow statistics can be used for a variety of purposes including, network traffic accounting, usage-based network billing, network monitoring, and data warehousing for marketing purposes.

NetFlow data records exported by routers and switches consist of expired traffic flows with detailed traffic statistics. These flows contain information about source and destination IP addresses along with the protocols and ports used in the end-to-end conversation.

This information assists IT in monitoring and fine-tuning network traffic by identifying additional bandwidth requirements, and allocating available bandwidth efficiently across the network.

NetFlow traffic statistics include

1. Time stamp of the flow
2. Source and destination IP address
3. Source and destination port number
4. Input and output interface number
5. Next hop IP address
6. Total bytes in the flow
7. Number of packets in the flow
8. First and last time stamps of packets switched as part of this flow
9. Source and destination AS, and prefix masks
10. Sequence number (version 5 only)