Usage on Switchports vs. Router SubInterfaces

Hello all,

We've currently got a bunch of machines hooked up to several 3550 and

2924 switches. In most cases, each machine is owned by a different customer, is connected to a different switchport, and is in it's own VLAN, connected via an 802.1q trunk to a 7200 series router, which has a bunch of GigaBitEthernet subinterfaces, one for each VLAN. We're using RTG to track usage through SNMP on the switchports. The intent is to capture the amount of traffic to the Internet they're using. In the occasional case where a customer has more than one switchport and they're passing a bunch of traffic between these switchports, AFAIK our usage info is pretty much useless.

My questions are these:

1. If I collect SNMP data on the GigabitEthernet subinterfaces of the

7200 series router, will that more accurately reflect what I'm trying to get? Or, in other words, will it at least exclude the traffic that is passing from switchport to switchport, because -- I think -- this traffic never makes it up to the router's interface?

1. Is there a better way to track this data? How are others doing things in cimilar situations?
2. Related to above: Should I be using NetFlow instead, and if so, what open source tools are available for dealing wit this data?

Thanks much!

Rick Kunkel