We have 36 Additinal Domain Controllers in remote branches. All are windows 2008 R2. In Data center, Root domain exist. We configured sites based upon the network and geographical locations. Eventho, respective ADC is up and running, client computets resolving Domain DNS from other DNS servers. Why clients not resolving from their ADC? We assigned preferred DNS IP address as their respective ADC in client computers. Any option is there to configure to get resolve from its respective dns server or in its own site.