OSX 10.6.8 upgrade disactivated my ethernet port.

Question

after having installed the latest upgrade of OS X 10.6.8, my ethernet port doesn't work anymore. I get the message "ethernet cable unplugged".
Does anybody have the same problem?

Answer 1

I have managed to get my wired connection working again. Read on for the gory details...
Couple of days ago I found the 2641278 thread you mention, and I also had no trouble with false MAC address until 10.6.8 update. Thankfully, none of my other three Intel Macs on the same LAN had the issue so I did not even notice it until I started looking into the issue after 10.6.8 update.
I do not think that ifconfig terminal command will be of use because en0 is not even available when the issue occurs under 10.6.8 (this is my speculation based on events I'll describe below).
I did finally got things working again on the afflicted iMac (27" i5 w/ built-in Broadcom 5764 network card), and here is how (the events described are spread over multiple days due to my time constraints):
I first removed the Ethernet device under Network preferences (as suggested by David earlier in the thread). But when I tired to re-add the interface it was not available! Btw, that's when I really got ticked off about David's post, but in the end it was what got me digging deeper and allowed me to ultimately solve my problem... for the time being :-) . So at this point I must thank David for his suggestion.
I tried rebooting, removing power... no dice, Network preferences panel still does not have the ethernet interface available for me to add. So I fire up the Terminal.app and that's when I observe that even ifconfing does not list en0 interafce!
Next I start up the System Profiler and there is nothing listed under the Ethernet Cards section! Wow... that's when I start looking through kernel.log for any clues and find the funny things going on with the MAC address along with the errors I posted about earlier in this thread. Further Googling points me to the above mentioned thread but nothing that would point to a solution (at this point I have already tried applying the 10.6.8 combo update without any success).
Since I have Windows XP installed under Boot Camp I start the iMac in Windows XP and wouldn't you know it, network works fine... I check the MAC address, still the fake one (00:10:18:00:00:00). As mentioned in 2641278 thread, this is a Broadcom MAC address. Next I download the Broadcom Management Application for Broadcom NetXtreme Server card and it tells me the same thing, fake MAC is what it sees on the card :-\
At this point I decide to reboot back to OS X, but on a hunch I choose to do it in Safe Mode (http://support.apple.com/kb/HT1455) by holding down a Shift key. Please note that I booted into Safe Mode right after being in Windows XP, I shutdown down the Windows XP (i.e. powered off the iMac) and when I powered it on I was holding down a Shift key.
Booting into Safe Mode took noticeably longer and you see a progress bar displayed on the screen as well (for a while it looked like nothing was going on, so be patient).
Once OS X is loaded I was presented with a login screen (when booting normally I have it automatically log me in, so that was different) and above the user selection window I could see Safe Mode.
Upon login I bring up Network preferences and even without me doing anything it notifies me that it has detected a new Ethernet! I acknowledge the dialog and interface is added. After a few moments the red dot changes to yellow while it is searching for DHCP server, and finally to green once it received the IP info from the DHCP server, awesome! I then change the interface config to my usual manual settings and also check the MAC address... it has a valid MAC address it used to have in the past!
I double check the kernel.log and find that errors I posted about before are gone as well.
I have since rebooted the iMac numerous times as well as completely shut it down and unplugged it from power without any issues. It has now been (only) two days since things got fixed so I hope issue is resolved.
In summary
remove the Ethernet interface from Network preferences panel
power off the Mac
boot the Mac into Safe Mode by holding down a Shift key on your keyboard
go to Network preference panel and let it re-add the Ethernet interface
(if necessary) re-apply your setting to the Ethernet interface
enjoy connectivity :-)
I hope this helps other people as well. Also, I don't think me booting the Mac into Windows was relevant to the solution, but it is yet another potential variable.