I fixed the speed of both Mac and PC to 100Mbps full - Reset AE, power cycle Switch, then added mac - speed 75Mbps. Added PC, both at 75Mbps. All is wel!. PC goes to sleep, wakes up back to 9Mbps on both. Both show link speed of 100 (fixed).
Question: how to a find the link speed of the Airport Extreme? Switch only has green LED so no clues there.
I also had a problem with both Mac and PC (different time) where they said cable disconnected. PC would connect until operating system up, then switch LED would go off and PC would report cable unplugged. Simular for Mac. I have seen other post with same problem.
The fix is to power off all systems and start again - all the other fixes suggest, change config etc in effect restart the router. I changed switches and cables with no effect.
Hence I think that the issue is the auto negotiation of the AE and re-start all system restart/refresh the auto negotiation. fixing the end client help.
it used to work ok, so what has changed. AE firmware?
Solution for me:
Use WiFI may only give 40MBps but it is better than 9Mbps !!!
I had this same issue rear it's head today, on 2 iMacs at the same time. While it says the cable is unplugged, the lights on both a router and a hub light up when the cables are plugged in to either machine. A third iMac on the same network is not suffering this issue.
SMC and PRAM resets did nothing.
I tried going into System Preferences/Network, then selecting ethernet and deleting it. When I tried to add it back, it was not a option. Ethernet was gone from the interface options. Somehow, overnight, 2 of 3 iMacs did this with no updates or other changes.
My interim solution is to use USB -> ethernet dongles, but I'd sure like to figure out what is going on here. All 3 iMacs are running 10.11.2, one is a brand new iMac (that one still works), the other 2 are 2 and 4 years old respectively.
If anyone has any suggestions, I'm open to hear them,
Just reboot, hold down the Comand & R keys, do a First Aid (as a safety measure) from the Disk Utility menu, then do a Reinstall OS (of course you have to be online somehow to do this. (My WiFi worked, so I used that). Once you've reinstalled the OS, your Ethernet port should work again. It did for me! (That's the quick way to do it - from Apple Tech Support)
Hi, I'm having a similar problem. All of a sudden my iMac won't connect to the internet through the Ethernet setting, tried lots of different things to figure out why. I opened Network utilities and discovered I'm missing the ethernet card and setting. I'm able to connect to the Wi Fi, luckily.
Tried doing a hardware test but couldn't. Finally found a message under Software....
Version 10.1.12 Reason Kext Exclude List Date Disable 9/16/15, 8:25 PM
Version 3.2.3 Reason Kext Exclude List Date Disable 9/16/15, 8:25 PM
Because of the date I'm not sure that this is the reason for my ethernet problem.
Does anyone know how I can re-install my ethernet card. Any help would be greatly appreciated.
Thank you for any consideration to this problem.
First, your Ethernet card will reappear when you shutdown and turn it back on again, so leave your WiFi connected, then...
Just reboot, hold down the Comand & R keys, do a First Aid (as a safety measure) from the Disk Utility menu, then do a Reinstall OS (of course you have to be online somehow to do this. My WiFi worked, so I used that). Once you've reinstalled the OS, your Ethernet port should work again. It did for me! (That's the quick way to do it - from Apple Tech Support)
First of all, sorry for my english, it is not my first language.
Today I turned on my Mac mini (latest version with latest version of el capitán) and found that ethernet connection was not working.
Trying to find a solution online, I have found this post.
I was worried that it was a hardware problem but it is really weird that this problem appears today to many people so I think it must be software related.
I have done SMC RESET without any luck. I can not do PRAM RESET because I do not have a keyboard, I use my iPhone to control the Mac mini.
I can not use the solution given here of configure manually the ethernet port to 100 because I deleted the service and when I was going to add it again, it has disappeared.
How do I reinstalll de OSX? Will I lose all my personal data in the process?
if anyone find a solution to this please let me know.
People who today are finding their ethernet not working are not helping themselves by trying to get an answer from this thread, which was started years ago. Tacking onto an ancient thread is a quick way of gaining out-of-date information.
The problem lies with a 'silent' software update which affects only Macs using the Broadcom BCM5701 driver, which the update inadvertently renders inactive. The various 'solutions' posted above prior to today will not work; a reinstall is necessary, either of the System or (possibly) the updated version of the update which is causing the trouble.. There is a discussion and proposed solutions in the more recent posts in this thread: