Fluke, Exfo, and a few other companies make ethernet test sets. Plug one in at one end of the network and one at the other end and start the test. By testing individual devices/links you should be able to isolate the problem to one or more devices.
For a fraction of the price, you can get the functionality you need using a couple of laptops and netperf.
There's no software/hardware that I know of that can simply be plugged in and test an entire Ethernet network and give you hop to hop information for each device and link. Ethernet is simply not designed in that structured of a fashion - most of the connectivity is negotiated p2p between each device and other devices are simply not aware of the rest of the hierarchy. The closest thing that you get in Ethernet would be spanning tree protocol (STP), which could tell you how far away you are located from the root switch, from which you could calculate link speed (not duplex) and hops. However, the root switch in a non-engineered network is likely just the switch that booted up first and has little relation to topology. Most non-managed switches do not support STP.
This leaves an ethernet admin having to review each switch for errors, duplex mismatches, etc. and sometimes testing individual links.
