Ethernet troubleshooting:
1) REALLY understand how Ethernet works; CSMA/CD, repeaters, segments, bridges, switches, physical cabling, collision and broadcast domains
2) Get to know the typical problems, what the symptoms are and how to fix them; physical problems, broadcast storms, excessive collisions, runts, jabbers, network loops (and spanning tree) etc
3) Tools - learn how to monitor and diagnose the performance on your Ethernet segment(s)
4) Apply 1) and 2) with the aid of 3) to work out a step-by-step approach to diagnose, isolate and correct any problem they throw at you.
