Ethernet MAC address has changed and I can no longer connect to the network

My MacBook Pro 17" (Mid 2010) did the same thing after applying the 10.6.5 update. My MAC address is now 00:10:18:00:00:00. No resolution yet.

I was able to reset my MAC to its default using the following command:

sudo ifconfig en0 lladdr 00:00:00:00:00:00

Where 00:00:00:00:00:00 is my NIC's native MAC. Unfortunately this is only valid until the MBP reboots - then it's back to 00:10:18:00:00:00.

Hoping for a fix...

I've the same problem on my iMac 27" core i7 middle 2010

only cmd alt+pr can resolve it, but not definetively.

apple care don't have any information on it

I've found that zapping the pram doesn't resolve the problem... the only thing that worked across reboots was manually setting the MAC back to its original value as I listed above... and even that stopped working after a week or so (and didn't work across reboots the first few times I tried it). I've had to manually restore it a few times.

There's definitely something going on, but I've got no idea where to start looking for an answer. I agree that AppleCare is not aware of anything on this yet.

All in all, this seems to be a difficult thing to recreate reliably, which makes it that much more difficult to track down.

Message was edited by: seigniory

I'm by no means an expert, but since you said that your ISP uses DHCP, you might find this article of interest:

http://en.wikipedia.org/wiki/DynamicHost_ConfigurationProtocol

Have you contacted your ISP at all? That would be my first call since it is their server assigning the addresses - the computer just picks it up automatically.

I have the same problem, but only occasionally. In my case a reboot changes the mac address back to what it should be.

I've been trying to find a pattern or cause, but I haven't come up with anything yet => reproducibility is null.

Could it be a BIOS problem? I found posts on HP machines with the same problem:

http://bizsupport1.austin.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c0 1731978&lang=en&cc=us&taskId=101&prodSeriesId=3687446&prodTypeId=321957

Message was edited by: Dalton#1

I'm having the same problem...
As a temporary solution, I created a script to change the MAC every time the issue occurs.

Did anyone get some response from Apple?
Because this is a major problem...

Or a permanent solution?

Oh yeah: is anyone using Time Machine with a linux server?

because the problem is appearing since I am backing up on a linux server...

Have had the same Ethernet ID changing to 00:10:18:00:00:00 issue. TWC is my service provider, and I contacted customer support for help. They do not have any idea what is going on, and they stated that it must be an OS X issue.

The ID change occurs intermittently regardless of whether I awake the from Sleep mode or from Shutdown. I've found one solution that has worked for me every time. I Shutdown the computer, and then unplug the power plug from the back of my Motorola SB4200 cable modem. I replug and wait for the modem to reboot. After the modem is running, I reboot my iMac. Each time, the correct Ethernet ID is displayed.

As a caveat, I found that when my Ethernet ID =00:10:18:00:00:00, my iTunes account repeatedly asks for me to verify my billing information. After reentering my credit card security code, I receive a message stating that the credit card has been declined. Trying other card numbers produces the same result. However, once I use the reboot method to correct the Ethernet ID address, iTunes works perfectly.

FYI: I do not use Time Machine or any other backup software. In addition, the Ethernet ID issue occurs whether or not I have AirPort enabled.

Message was edited by: bswins

Additional detail:

The Ethernet ID issue and the iTunes billing verification issue both appeared after the 10.6.5 update.

I informed Apple Support, but have not received a reply. If others first noticed the address issue after the 10.6.5 update please inform Apple.

Dear all,
I am having the same problem with a new MacBook Pro, bought end of October - for me it became apparent for software (Matlab, Comsol) that are registered with a licence file which was created based on the MAC address, and also when trying to register the computer to the company network. That software will only work those times that the computer "knows" its real MAC. Also, I found that audible audio books, managed through itunes, will not synchronize with the ipod at those times when the MAC address is at the producer's default (00:10:15:00:00). I never had network issues other than this computer registration, - no probs at home or elsewhere - , so it will depend on the individual setup which issue users observe.
I have had long phone discussions with different Apple support people, they have done checks based on Capture Data that I sent to them via email, etc.. They can't find the problem in the software/setup and they advised me to go the Genius Bar and have those guys look at the computer's guts.
Restarting sometimes did set the MAC to the real one, also running the code that someone suggested in Terminal sometimes helped.
Other than that, looking through the web, it does not seem to be an Apple-unique problem, but certainly one would like to see support to take care of that issue for Macs soon.
Also, thanks a lot for this thread! Otherwise the support guys on the phone would not have believed my : "the Mac address changes on a daily basis" and would just have brushed me off.
All the best,
Susanne

Message was edited by: semperula

This is definitely an issue locally to MacOS - it's misidentifying the NIC's MAC address before the OS even thinks about interacting with other systems.

DHCP servers (and applications that have licensing depending on a machine's MAC) are being fed bad information, and when that happens, bad things (tm) happen. Garbage In, Garbage Out. 🙂

UPDATE: it's been about a month since I first posted on this topic, and my MBP seems to have "stabilized" on this issue. I haven't had to manually set the MAC address from Terminal in quite some time.

That being said, I still haven't been able to reproduce the problem, and I haven't kept very good track of what I did to "fix" it, either. I've also probably jinxed myself with this post, so I fully expect to wake up to a bad MAC again tomorrow.