Sometimes it’s necessary to figure out which Global Catalog (GC) your Exchange 2010 is using.

  • Open EMC
  • Go to Server Configuration, right-click each server and choose Properties and go to System Settings tab.

You can also look for Event ID Event ID 2080 in the Application logfile and KB316300 gives you an idea what this means.

To force it to use a specific GC:

  • Open EMC
  • Right-click Organization Configuration and choose Modify Configuration Domain Controller:
  • Choose the default (Exchange will select for you) or select a domain and GC manually:

Now hoes does Exchange select which server to use? Quote from Microsoft Exchange 2010 Best Practices book:

All Exchange 2010 servers use DNS to locate a valid domain controller or global catalog. By default, each time a domain controller starts the Netlogon service, it updates DNS with service (SRV) records that describe it as a domain controller and global catalog server, if applicable.

SRV resource records are DNS records. These records identify servers that provide specific services on the network. For example, an SRV resource record can contain information to help clients locate a domain controller in a specific domain or site. For that reason, the SRV records for domain controllers and global catalog servers are registered with several different variations to allow Exchange servers locating a suitable domain controller or global catalog during the Active Directory discovery process.

One option is to register DNS records by site name, which enables computers running Exchange Server to find domain controllers and global catalog servers in the local Active Directory site. Exchange Server always favors the selection of a domain controller and/or global catalog from the same site that Exchange is installed into.

Here is an example of an SRV record: IN SRV 0 100 389