WINDOWS DNS

Sir,

I have one windows 2003 domain, with 192.168.1.X subnet mask 255.255.255.0, i have one member server (additional DNS, read only copy)this member server IP 192.168.1.X with 255.255.255.0, this member server has two NIC one for lan IP one for WAN(VSAT IP). i installed ISA server on member server.In this member server i configured DNS forwarder with the ISP IP address. i given DNS IP to all clients the member server LAN IP.

Now if i install ADC Root DC, is it work if the root DC fail, here i have one dough how th ADC resolve DNS coz i given DNS IP for clients member server IP so how the ADC will resolve the DNS queries.