We have a Linux router which firewalls incoming traffic, while allowing the 300+ hosts on our local network to make outgoing connections to the Internet.
I suspect that a few "bandwidth hogs" may be consuming far more than their share, and degrading the experience for the other users. I would like to make some measurements on the Linux router to determine if that is true.
I've Googled for bandwidth usage monitoring tools, and found a bunch of tools which can measure bandwidth usage "by IP". But I suspect this means the destination IP, not the source IP. I don't care about the remote IPs -- I just want to know which IPs (or better yet, MAC addresses) on the local network are consuming the most bandwidth.
Is there a freely available program for Linux which can help?