I've recently took over responsibility of an Exchange 2013 Organization that is deployed as follows:

Active Directory consists of 4 Sites. AD Site A, B, C, D  Exchange 2013 Enterprise resides in 2 of the 4 AD Sites as follows:

AD Site A - ExchangeServer 1 and ExchangeServer 2

AD Site B - Exchange Server 3

AD Site C - No Exchange Servers

AD Site D - No Exchange Servers

All 4 AD Sites are 4 different Physical locations/datacenters. All 3 Exchange 2013 servers are multi-role servers.

The Forest in which Exchange resides in consists of an empty Root domain, a Production (child) domain and a Test (child) domain. Exchange resides in the Production (child) domain.

Issue: AD Site A contains DC's from all 3 domains: Root Domain, Production child Domain (this is where Exchange lives) and Test child Domain. I notice that Exchange in AD Site A is using DC's from the Root Domain for it's "DefaultGlobalCatalog", "DefaultConfigurationDomainController" and "DefaultPreferredDomainControllers" This to me does not seem to be very efficient as any Address Book queries will have to be referred to by the Root Domain DC's to the Production child domain where Exchange lives. All of the AD User accounts and mailboxes are in the Production child domain.

In a situation such as this, would it be advisable to build 2 additional AD sites specifically for Exchange? Rather than re-IP Exchange or risk the impact of moving several other (non exchange) servers to another AD site, I would add the IP address of the Exchange servers /32 to the new Exchange dedicated AD Sites and erect a DC in these new sites adding its IP address /32. Any thoughts on this idea? If the subnet that exchange resides on is (for example) 10.60.3.0 /16 in AD Site A, and I build a new AD site for Exchange and add the IP address of the Exchange server such as 10.60.3.141/32 for this new Exchange AD Site boundary, I can still leave the 10.60.3.0 /16 unaffected in AD Site A, correct?

I'm looking for Microsoft's best practices in terms of laying out AD and domain controllers pertaining to Exchange server 2013.

• Edited by Anthonyray66 12 hours 26 minutes ago addition

Is this causing you any problems or are you just overthinking things?