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Setup Netflow Collectors

Netflow is a great feature which provides detailed information on connection flows passing through your router or switch. You can use the data raw from the IOS CLI or export it to a Netflow collector for graphing and analysis. There are many free software packages out there for this and a google search will point you in the right direction.

To get Netflow up and running you first need to configure the interfaces you want to get the flow data from.

interface serial0/0
ip flow egress
ip flow ingress

The Egress command obviously turns on NetFlow for transmitted data whilst Ingress is data into the interface. (On older IOS version ip flow ingress was turned on with the command ip route-cache flow)

Now we can configure the NetFlow collector we wish to export the data to.

ip flow-export source Loopback0
ip flow-export version 5
ip flow-export destination x.x.x.x 9996

The first command specifies the interface the NetFlow data will be sourced from. In this case we are using a loopback interface. We then set the version the collector expects the data to be presented in. The options currently are 1, 5(the most common) and 9 (the newest). In this case we are using version 5. Lastly we set the destination IP for this NetFlow traffic (our collector) and the port number. Thats all there is to it on the router side. You then just need to setup your collector to expect the traffic on this port in version 5 format and add the device.
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