www.faqs.org (http://www.faqs.org) has all the documentation for Ethernet protocols, pretty much going back to smoke signals. The important and intelligible ones are:
UDP Protocol:
http://www.faqs.org/rfcs/rfc768.html IP Protocol:
http://www.faqs.org/rfcs/rfc791.html ICMP Protocol (Useful to ping devices):
http://www.faqs.org/rfcs/rfc792.html TCP:
http://www.faqs.org/rfcs/rfc793.html Also, an excellent tool you'll need is Wireshark, which lets you look at messages going through your computer's Ethernet port.
Edit: Wireshark is a piece of software, from
Wireshark.org