Accesing an external server with a pure domain name

I have a server on the internet with the name, say, “” and my UCS domain is also “”. Inner servers, with UCS have names, etc. Before upgrading to UCS 5.0 I could reach my external server via, now DNS server on UCS on request for IP of gives an IP of the domain controller.
How to set up it, so for the IP of UCS DNS will again request an external DNS server?