There are two commands to implement NETFLOW on a interface
ip flow ingress
ip route-cache flow
you can use them for each purpose.
if you apply “ip route-cache flow” on a interface, then the sub interfaces also are applied
but if you want to apply on specific interfaces, you can use “ip flow ingress” on each interfaces.
there are also global commands to implement NETFLOW.
ip flow-export version x (x=1,5,9)
ip flow-cache entries x (x=from 1024 to 524288)
ip flow-cache timeout active x (x=from 1 to 60 minutes)
ip flow-cache timeout inactive x (x=from 10 to 600 seconds)
if you use NETFLOW version 9, you can use “ip flow egress” on a interface.
if you have a plan to install NETFLOW server in the future, you need to consider the below commands
ip flow-export source
ip flow-export destination
you can check the list of cached flow using below
show ip cache flow
if you are interested in impact on a router, you can check this link
there is easy way to find out which traffic is the chatty in global command
top number x (from 1 to 20)
and then you can check the list of top talkers using below
show ip flow top-talkers
don’t forget to configure ip flow ingress or ip cache flow command on your interface.