I've just started messing with the official ethernet shield, the older version, not the newest. I think version 4. I uploaded a webserver example and hooked it up to a near by hub that one of my desktops also plugs into. when the arduino and ethernet shield are plugged in and powered up, I can barely connect to it with a browser. it seems like a lot of interference or something. it either never connects, or it downloads part of the text then never finishes. my desktop shows the same symptoms and seems to lose connection to the network. the RX led of the ethernet shield is very active.
the hub is a hub, not a switch, so all data being sent to or from my desktop should physically make it to the ethernet shield too, but it should be ignored by that device because it's not the right destination. to me, it seems like the ethernet shield is maybe stealing the data from the desktop and causing it to not function. if I take the arduino out to my server closet and plug it into a good quality switch, it works fine. that's what leads me to my previous conclusion, because a switch only sends data to the ports of the right destination. a hub sends data to all ports. actually, now that I think about it, I do remember having a similar problem using the nu electronics ethershield on a hub also. I believe the problem I found there was it was accepting packets that don't belong to it. so is the arduino just not compatible with hubs and only works with a switch?
