Exchange 2013 Cumulative Update 15 Issue

I am getting the following error when attempting to install CU15 on one of our exchange servers.

Setup can't use the domain controller 'Site' because it belongs to Active Directory site 'Main Site'. Setup Must use a domain controller in the same site as the computer (other mail server).

The server that is getting the error is setup as our other sites mail server. All of the mail accounts are linked from the other sites DC. I cannot move the server to the main site.
Brandon MillerSystems AdministratorAsked:
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Scott CSenior EngineerCommented:
Use the command below to set your exchange server to the correct domain controller.

Set-ExchangeServer -Identity EX01 -StaticDomainControllers -StaticGlobalCatalogs

You can use the command "Get-ExchangeServer -Identity EX01" to see what your current DC is on that server just to check.

I found the above here ....

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Brandon MillerSystems AdministratorAuthor Commented:
Im not sure I can change it to the main site without causing isues with the trust we have with the other domain?
Scott CSenior EngineerCommented:
You may have to.  Setup need to use a DC that's in the same site as your Exchange server you're trying to update.
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Brandon MillerSystems AdministratorAuthor Commented:
Oh gotcha once the update is complete I just need to move it back to the other site for normal operation? Basically move the server site over to the mail domain and perform the update then change it back?
Scott CSenior EngineerCommented:
That should work. Or just make the change, do the update, leave it and see how things work.  If everything works as it should, just leave it, if you have any interruption, then change it back to the way it was.
It's required to have a DC in the same site as Exchange.
I highly recommend exploring this approach and deploy AD DC in the same logical LAN as Exchange.
There's a lot of communication going on between Exchange and DC.
Brandon MillerSystems AdministratorAuthor Commented:

The mail server that I am updating is for the specific site where their DC resides, the main site does not have any of their user accounts that access it.  However, since they are simply linked accounts within the mail domain I guess it would make sense that the Exchange server would need to be on the same site as the MAIL DC's since we have an trust between the mail domain and the external site.

here is a cut from the results:
Get-ExchangeServer -Identity (Problem Server)
(MAIN SITE FQDN)/Configuration/Sites/External Site

Get-ExchangeServer -Identity (Server that update worked on)
(MAIN SITE FQDN)/Configuration/Sites/MainSite
I'm not sure if I understand your explanation.
How many domains/forests do you have? You can substitute the real names with,, etc.
Also, indicate how many physical sites there are as well as what is located in those sites.
Specifically, provide example of the name for the DCs as well as the FQDN for the Exchange.
Brandon MillerSystems AdministratorAuthor Commented:
We have several sites

MainSite/Campus: (5 domains within forest)
mail domain: (Contains mail servers with trusts between sites)

external site/domain: (Trust between mail domain and external site) linked accounts.

Im not entirley sure how its setup because I started working here after everything was setup. Some of it just leaves me scratching my head as to why it was setup that way. The odd thing to me is when I look in sites and services the MailServer that wont update is not showing up in the main sites and services even though the site results from the powershell show it in there.
Brandon MillerSystems AdministratorAuthor Commented:
OtherMAIL  (Problem Server)      

Not sure if this helps clear it up at all.
So the recommended approach as I mentioned before, it to have a DC per site where Exchange is located.
The server is not supposed to show in the Sites and Services since it's doesn't provide any services to users, on the domain level.
If you have subnets correctly populated, it knows that it belongs to another site, hence the error message.
You might be able to still install the CU using the approach provided by Scott C. Nothing wrong in doing the suggested approach, I don't believe it will break Exchange.
Brandon MillerSystems AdministratorAuthor Commented:
I was able to update the server without changing the Site assignment. I simply added the site in the registry. The update pushed through without any issues.
Enough information provided
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