February 8, 2006 tools

Network bandwidth usage monitor?

Sometimes, for no reason I can discern, the network bandwidth on various computers in my house goes south. What I'd love is a tool that shows me how much traffic is going across my network, where it's going and where it's from, i.e. from the internet, from a machine in my house, etc. Ideally, it'd also show me the ports and even the processes on each machine that are producing/consuming the data. Does such a tool exist?