My new Mac Pro had a strange problem. When I turned on the Mac or woke it up from sleep it had no ip anymore. The only way to fix this problem was to switch the cable from ethernet 1 to ethernet 2. Sometimes I had to repeat this step, turn wireless on and off and finally I got an ip. When I restarted the router I did not have to switch the cables, then I got an ip immediately after the restart.
I searched on the internet and found several solutions:
- Reset PRAM
- Remove and add the ethernet connections
- Check the cable (the cable worked for years on my MacBook Pro)
- Try different ports on your router
None of these succeeded. I decided to contact Apple within a few days but first I searched again on the Internet. I found this page which described exactly my problem. The interesting part of this thread was about the FritzBox since I do have this router as well. The thread suggested to disable energy saving mode on the ethernet ports of the router. Which turned out to be the solution! Now my network is immediately connected after a reboot or wakeup.