[CentOS] How to find out what's eating the bandwidth

Is there a program that will tell me what's eating the bandwidth on a lan?

I'm thinking of something that would tell me that a.b.c.d is using so many mbps and a.b.c.e is using this many and so on.

Or can just-another-computer-on-the-network actually see that sort of information? I don't know enough about the low level nuts and bolts of networking to know if it has that kind of access. I'm really just interested in volume of traffic per attached device rather than specific origin/destination information if that's easier to obtain.

This way if something is eating the network I can find out what it is without having to start unplugging cables and so on to find out when it stops.