It all depends upon what you define as "system."
In the strickest sense of the term, it can mean which host. In the looser sense it can mean which application which could involve a series of hosts.
To find out which host is sending and receiving the most packets, then most protocol analyzer products will give you a Top Talker report. I favor the Network General Sniffer / Reporter set of products. They do decent reporting and EXCELLENT troubleshooting. They also cost (in some cases a great deal of ) money.
If you mean free network monitoring product then you have to get real creative.
MRTG (
will graph packets in / out of each port of your server farm switch. Integrate RRDTool with it (
can then write a script that will query the rrdtool files for the top talkers.
Another option is FlowScan (
It will show you the "flows" through any device that can output flow data. This option will require a lot of effort to make work. But it has the possibility of showing you your application utilization and is by no means simple.
What you are asking for may sound simple, but the underlying structure needed to obtain those kinds of reports is not. To get the information means either exerting funds or time and energy or ususally both.
Patrick
Patrick Bartkus, CCNP, CNX, SCM, RHCT Sr. Network Engineer
GA Dept of Labor IT Network Services
If truth were not absolute, how could there be justice?