NetFlow is a network protocol designed by Cisco which is used for collecting IP traffic information and monitoring network flow. By analyzing NetFlow data, you can get a picture of network flow and volume.
Traffic can be grouped and analyzed based on different criteria like interface, source IP, destination IP, IP protocol, source/destination TCP/UDP port and service type.
Routers and switches that support NetFlow can collect IP traffic statistics as NetFlow records towards at least one NetFlow collector server that does the actual traffic analysis.
Popular NetFlow Analyzer Software
Popular NetFlow Analyzer Software Solutions are: SolarWinds NTA (NetFlow Traffic Analyzer), ManageEngine NetFlow Analyzer, and Paessler PRTG Network Monitor
How to Configure NetFlow on Cisco Switches/Routers
R1(config)#ip flow-export destination 10.0.0.2 2055
R1(config)#ip flow-export source Fa0/0
!
R1(config)#interface Fa0/1
R1(config-if)#ip route-cache flow —- !(track the flows on this interface)
Traffic flows on fa0/1 will be exported by f0/0 on R1 to Analyzer.