Working in technical support I get asked a lot, “I enabled NetFlow on my router, why don’t I see outbound traffic?” This is because NetFlow version 5 only supports ingress flow monitoring and they don’t have NetFlow enabled on all interfaces. In NetFlow v5 outbound traffic is calculated by the idea what goes in must go out (or stop at the router) so, it’s necessary that all interfaces are monitoring ingress traffic to get an accurate representation of outgoing traffic. So, if ingress monitoring has been working great all along why enable egress monitoring?
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