If you running DNS server on a machine other than that on which you have installed Primary HC Setup, then you have to install Hosting Controller Secondary setup on the machine where DNS is hosted and do the following settings on both Primary and Secondary HC installations.
Configuration On Primary Machine:
Enable remote DNS:
In Start menu Programs folder, go to NT Web Hosting Controller and click Settings. The Settings utility dialog will appear.
In Settings dialog, click on Servers tab, check the DNS on Remote Server check box and provide the IP of the server where DNS is running in DNS Server IP box.
Click OK to apply the new setting.
Configuration On Secondary Machine:
Enable local DNS:
In Settings dialog, click on DNS tab and check the Enabled check box.