As I said in my previous article Direct Access is an IPv6 only technology; Direct Access clients talk to Direct Access Server using IPv6 technologies. (Don’t forget this communication happens using IPv6 transition technologies i.e. IPV6 encapsulation in IPv4 packets.). As client to server communication happens using IPv6, Name lookup also happens using IPv6 & AAAA query. So if a internal server has IPv6 address it is easy for the client to start communication.