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

Question

I have a new iMac, 21.5" running 10.6.4. It was purchased in the past month.
I am using it on an ethernet network and using DHCP to obtain the address. It has been working for the past few weeks. I turned it on today and it is failing to connect. After some digging around, it seems that the MAC address (Ethernet ID) has been reset to 00:10:18:00:00:00. This is different to the one it has been using last week.
I have not changed any network settings. Airport is working fine.
If I pull out the ethernet cable and reinsert, the machine tries to obtain an IP address. After a while, it returns with a self-assigned IP Address.
Last week, I did notice that it was taking a relatively long time (a minute or so) to obtain the IP address over ethernet. Plugging the same ethernet cable in a macbook, I am able to obtain the IP address for the macbook much more quickly.
I see that I could use ipconfig to change the interface address to what I believe is the correct address. Would this be sensible?
Why would the machine have reset the MAC address anyway?
Regards,
Neil

Answer 1

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