Specify a preferred server in Directory Utility on Mac
On a computer that’s configured to use Directory Utility’s Active Directory connector, you can specify the DNS host name of the server whose Active Directory domain you want the computer to access by default.
If the server becomes unavailable in the future, the Active Directory connector reverts to another nearby server in the forest.
If this option is deselected, the Active Directory connector determines the closest Active Directory domain in the forest.
In the Directory Utility app on your Mac, click Services.
Click the lock icon.
Enter an administrator’s username and password, then click Modify Configuration (or use Touch ID).
Select Active Directory, then click the Edit button (looks like a pencil).
If the advanced options are hidden, click the disclosure triangle.
Select “Prefer this domain server”, then enter the DNS host name of the Active Directory server.