2

Question:

Which tool could I use to monitor and break-down in real-time which bandwidth is routed by iptables to which computers?

Context:

I have a linux box masquerading about 15 devices to internet with iptables with 3 ethernets (2 LAN, 1 WAN).

From time to time, a user consumes all the ADSL bandwidth.

I use bwm-ng for monitoring the traffic and I see a result like this one:

$ bwm-ng
  bwm-ng v0.6 (probing every 0.500s), press 'h' for help
  input: /proc/net/dev type: rate
  /         iface                   Rx                   Tx                Total
  ==============================================================================
             tun0:           0.00 KB/s            0.00 KB/s            0.00 KB/s
             eth0:          31.35 KB/s          649.82 KB/s          681.18 KB/s
             eth1:         649.40 KB/s           33.84 KB/s          683.24 KB/s
             eth2:           0.00 KB/s            0.00 KB/s            0.00 KB/s
               lo:           0.00 KB/s            0.00 KB/s            0.00 KB/s
  ------------------------------------------------------------------------------
            total:         680.75 KB/s          683.66 KB/s         1364.42 KB/s

So I see that traffic received on eth1 (WAN) is routed to some IP into the eth0 (LAN), so someone is making a mega-download.

The thing is that this user uses to consume all the bandwith for hours.

I could discover who is this by doing the following:

  • Cutting access to some IPs and observe bwm-ng, then cut others and so. But this is dirty. It would interrupt the service and I don't want to do that.
  • Instructing iptables to log all traffic and trying to read the logs, but I think this is like much more painful with respect a tool that displays this over the ssh already digested in a manner similar to that of bwm-ng.

No need of historical data, nor fancy graphics. Just real time info and text over ssh (like bwm-ng) would be perfect.