Click Start, click Administrative Tools, and then click on Active Directory Sites and Services.
2. In the details pane, right-click NTDS Settings and select Properties.
3. On the NTDS Settings Properties and select the Global Catalog check box and click OK.
Note : You can enable the global catalog role by using the command line.
1. Log on to a domain controller.
2. Click Start, and then click Command Prompt.
3. In the Command Prompt window, type the following command:
repadmin /options servername +IS_GC.
If in cause GC not available current DSA :none.