Bandwidth montioring at the user level

Question

I'm considering a mac mini server with Snow Leopard. One of the things I want to implement is a user level bandwidth monitor and domain level monitor. I expect to at have at least 3 groups using the server. I want to monitor or even limit their monthly band width usage, so that the server doesn't go over it's monthly allotment from the host.
Can anyone point me to how this could work? Is it ntop or squid or something else?
Thanks,
ChrisP.

Answer 1

I think you're confused about how this could work.
Unless the server is acting as the internet gateway, there's no way this can work at all. Typically clients send their data directly to the network router and this traffic wouldn't be seen by the server at all, therefore there's no way to monitor it.
If you use Squid you'd be able to track web usage per client, but that wouldn't count any traffic that doesn't go through the proxy (e.g. email, IM, P2P, DNS, FTP, etc., etc., etc.) - in other words it would only give you a partial picture.
Even if the server was set as the gateway and could monitor all the traffic you still can't do this on a per user basis - all you know is that a specific client IP address generated (or received) a certain volume of traffic. You have no idea which user on that system generated the traffic.
This might not be a big deal on machines used by individuals, but would be near impossible on a multi-user basis. Either way there's no 'group' concept.
The way this is typically done is via traffic accounting systems built into your router and/or switch. The switch can monitor traffic throughput per port, so you can tell which machines send what volume of traffic. The router can do similar tracking, and should have the ability to track internal vs. external traffic (e.g. you might not charge for traffic to/from internal machines, only to/from the internet).