Is your mac mini ethernet port not working or has stopped working after you’ve changed something in your network, or just added one to your existing network?
Today I was configuring a brand new Mac Mini with OS X 10.7.4 server on it and I had it plugged into a Meraki MX80 and it was all working just peachy. Then I moved the Meraki and plugged it into a Cisco SG300-28 managed switch and the ethernet port on the mini stopped working.
I went into System Preferences > Networking and could see that it was doing a flip/flop every 30 seconds or so, confirmed by checking the kernel.log. I did a bit of searching around and people had all kinds of things to say about cables and speeds and brands of switches but no real solid solution. One mentioned how flow control could be an issue.
I logged onto the cisco, checked the port that the mini was plugged into, flow-control : disabled. Ok then, I’ll enable it and see how I go, No Dice. There was one option left, auto-negotiate. I selected that, saved the config and bingo, my mac mini was back up and working.
So if you’ve got a switch you can mess with flow control, change it to Auto Negotiate and you’re up and running, well I was anyway. I hope this helps someone else.