Usage: Dfsutil /Server: /PreferLogonDc: /Set This can be used to set the PreferLogonDc registry value in a Domain Controller ...

Usage:
Dfsutil /Server: /PreferLogonDc: /Set 
This can be used to set the PreferLogonDc registry value in a Domain Controller
running OS Windows Server 2003 or above to the value provided.
The valid values can be 1 or 0

This could be used to display the value in a DC as well

dfsutil /Server: /PreferLogonDc /Display