I recently updated a 7200 series router to a 7600 series – quite a big change. The config used was exactly the same and I couldn’t for the life of me work out why netflow was showing such a small amount of traffic. In short it turns out you need to enable something called NDE (Netflow Data Export). Without this enabled the router will only export flows for the MSFC which is mainly management traffic.
All you need to add is the following line in addition to the normal flow export lines:
mls nde sender version 5
The following guide was quite useful for this: http://www.cisco.com/en/US/docs/routers/7600/ios/15S/configuration/guide/nde.html
So if you’re using an RSP720 or similar and find that you’re not seeing as much traffic as you should be when enabling netflow then this is likely why.
Hope this helps someone.