Follow these steps to make sure Active Directory is using the domain controller you want:

1. Verify DNS Settings: Double-check the DNS server settings to ensure they match the IP address of the specific domain controller you are using.
2. Check replication: Make sure that the domain controller you specify is configured to replicate with all other domain controllers in the domain.
3. Run Group Policy Update: Use the Force Update option on the Group Policy Management Editor to force an update for all machines on the domain.
4. Check authentication: Verify authentication requests now use the domain controller you specified by running a packet capture.