I've been noticing some problems with my 27" iMac recently where the Ethernet port has no IP address when waking from sleep and powering on. Seems to fix itself shortly after, but I put it down to some sleep issue. Today though, I installed a new network switch and could not get the iMac to connect over Ethernet. Tested the cable OK, switch ports with other machines etc. After a few hours, the Ethernet port came up. I was just wondering, before I phone Apple, is there any way for me to run diagnostics on the network port? I'm not going to lug this thing to the Apple Store only for them to not find anything wrong with it, but I feel like I've eliminated everything else from the equation now. Any ideas? Thanks, Mike.