NetFlow is a tool used to export flows of traffic that transit through an interface on a router.
NetFlow version 5, 8 and 9 support IPv4, only version 9 supports IPv6, the default transport used is UDP.
Flows should be analyzed locally in the router or sent to a NetFlow Server periodically to permit a deeper and more convenient analysis.
IMPORTANT NOTE: Check CPU Usage of the Cisco Device prior to enable NetFlow. NetFlow caching could be very CPU Intensive, in High-Traffic operating Devices!
Cisco commands used on NetFlow Configuration:
NetFlow server updated frequency (in minutes):
ip flow-cache timeout active 1
NetFlow Version (5, 8 and 9 support IPv4, only 9 supports IPv6):
Netflow server destination IP and port:
Interface-Level command to enable Netflow for ingress and/or egress Flows:
Source interface for communication with the Netflow server:
Some Verification and Configuration checks:
Example to activate ingress and egress flows exportation every two minutes on interface Gi0/3, and updates the NetFlow server (NFDUMP on Ubuntu 12.04 LTS Server) using NetFlow version 9.
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