Sniffing Ethernet Shield Traffic

I have an Ethernet shield that is not responding correctly when overloaded with traffic. I’d like to see what is causing it to stop responding. Does anyone have any idea how I can troubleshoot this?

Wireshark http://www.wireshark.org/ is free, open source, and with a good support forum.

It will - Let you see the contents of your ethernet packets - Decode many protocols for you - Allow you to write your own decoders for unusual protocols

It is not too difficult to download use - I managed it :)