If you want to force the Exchange server to use a specific GC instead of letting the server automatically choose a GC, you can perform the following steps:
- Start the Microsoft Management Console (MMC) Exchange System Management (ESM) snap-in (Start, Programs, Microsoft Exchange, System Manager).
- In the treeview pane, navigate to Administrative Groups, <administrative group name>, Servers.
- Right-click the server and select Properties.
- Select the Directory Access tab.
- From the Show drop-down list, select Global Catalog Servers.
- Clear the “Automatically discover servers” check box.
- Click Yes in the confirmation box.
- Click Add.
- Enter the name of the GC to use.
- Click OK.
Microsoft recommends that you don’t manually set the GC that Exchange Server uses; therefore, you should manually set the GC only when it’s absolutely necessary.