Using Netflow

Ever needed to track specific flow of information or find out what ports a application is using, or verify if your QOS is working correctly? Cisco Netflow is the answer.

NetFlow is a Cisco IOS application that provides a rich set of traffic statistics on packets flowing through the router, both ingress and egress. A NetFlow network flow is defined as a unidirectional stream of packets between a given source and destination. These key fields/statistics define a unique flow:

  • Source IP address
  • Destination IP address
  • Source port number
  • Destination port number
  • Layer 3 protocol type
  • Type of service (ToS)
  • Input logical interface

If a packet has one key field different from another packet, it is considered to belong to another flow. Flows are stored in the NetFlow cache and does does consumes additional memory, but generally this is not to much of a problem. Netflow data could be exported, but here I’ll show how to use it on CLI and how to interpret it.

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