Changing the Weight and Priority of a Domain Controller
By default all Domain Controllers have a weight of 100, the heavier the weight the more often the Domain Controller is referred to. If there are two servers in a site and one has a weight of 100 and the other 200. The Domain Controller with twice the weight will receive twice the referrals.
To modify the weight of a Domain Controller the registry key, use: HKLM\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters\LdapSrvWeight
By default all Domain Controllers have a priority of 0, the lower the priority the first in priority. The Domain Controller with the lowest priority in the site will receive ALL authentication requests unless it is unavailable. If the lowest priority Domain Controller is unavailable then the next lowest Domain Controller in the site will receive all requests.
To modify the priority of a Domain Controller the registry key, use: