Two DCs with the same domain name but never join eath other

One of my clients used to have two windows 2003 Domain Controllers and they were in the different locations. Both DCs  have the same domain name but they don't join each other (e.g. DCa and DCb are the same name mydomain). Now, they close one of the offices and move DCb to the DCa office. The DCb also has Exchange 2003 installed. What is the best way to make them work together?

1. If they demote the DCb server and join in the DCa, does the exchange need to re-install?
2. I assume if they demote DCa and then join it in the DCb, the exchange should work, but we need to rejoin all workstations. Right?

Or any better options?
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Lee W, MVPConnect With a Mentor Technology and Business Process AdvisorCommented:
No way I'd demote DCb with Exchange on - that can break exchange and I don't think a simple reinstall fixes (never tried, in fairness).  You could TRY to do a domain rename on DCa then create a trust between the two and OPTIONALLY use ADMT to migrate the workstations from what was DCa to DCb's domain.  Frankly, I'd not want to mess around - I'd just rejoin the workstations (using your option 2).
DatedmanConnect With a Mentor Commented:
You can demote a DC with Exchange on it if there is another DC on the *same* domain.

Are you saying that these are two domains with the same name but *not the same domain*?  If so I don't think you can make the two talk to each other, or not easily anyway.

I'm guessing the cleanest thing you can do is export the mailboxes on DCb with exmerge, create accounts for the users on DCa, import the mailboxes on DCa, quit DCbs's domain with any desktops and join DCA's domain DCb isn't being used--make sure everything is working well up DCb, uninstall exchange, demote to standalone server and join the other domain, then install exchange again on that machine if needed.
If someone else has a magic way to make 2 domains of the same name into one I sure wanna hear it. :)
Lee W, MVPTechnology and Business Process AdvisorCommented:
> You can demote a DC with Exchange on it if there is another DC on the *same* domain.

Datedman - What are you talking about - you break exchange doing that!
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MesthaConnect With a Mentor Commented:
You can DCPROMO an Exchange server.
If you want to practise your DR strategy.

It is not supported and more often than not break Exchange.

In this scenario I would be looking to scrap one of the domains completely, the one without Exchange and move everything across in to the main domain.

You cannot pickup Exchange from one domain and expect it to work in another, so if you wanted to go the other way it would have to be a complete extraction of email from the database and a wipe and reinstall of Exchange - which of course puts data at risk.

Nope leew, I demoted an exchange server right here on my own domain.  Was a DC, isn't anymore.  Nada problem in my experience.  ofc i never read up on it beforehand so if you say it's strictly verboten i'll believe ya...well, long enough to try it again in a vm for the heck of it. :)  Can't unjoin the domain but haven't had any problem with un-dc'ing it.
Oh hmmm did smith, did you mean that they both have exchange or that only DCb has exchange?  My have misread your post.  How many workstations (that are active) are in each domain?
If you ran DCPROMO on an Exchange server and Exchange worked correctly, then you were lucky. It is not supported by Microsoft and will usually result in Exchange failing. On that basis it is not something that you should be suggesting to others to do. That is basically the same as saying that you crashed your car in to a tree, walked away and telling everyone else that they can do the same thing because you have done it once or twice before.

OK i just read up and now i remember having to deal with changes in the IIS accounts etc.  Like  I said *cough cough*, leew and mestha are completely correct!  Anyway fortunately in this case it doesn't mean too much because either he's going to have to ditch one of the domains entirely to put the two machines on one domain.
smith9069Author Commented:
Thank you for all inputs. We re-installed teh DC and Exchange.
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