Sorry if this discussion has been had recently but

I know there is a way to do this, but what is the absolute Defacto best method of tracking flows from Cisco/Juniper routers? I know there is some freeware available such as cflowd but we really need something that will alert us to trouble before it becomes a problem. We don't mind buying an appliance to do this, and it doesn't have to be freeware software, we just want something that will work. Thanks, -Drew