How to use another DNS Server when the PC is not in domain?

I have two DNS servers (on DCs) in my domain that my clients use when they are connected direct in office or with VPN. I want to set up another external DNS server, and tell the PCs to use this server when they are not in domain. Is this possible via a script or GPO?

Thank you for the answer Emil, Esa is right, my Laptops are all already joined in a domain, i need a script to detect when the laptop is connected with the domain and when not. I have adapted your script to :

if ((Test-ComputerSecureChannel) -eq $true) {

write-host -fore green "I am domain joined!"

} else {

write-host -fore red "Ooops, workgroup!" }

but it doesen't always detect the domain, don't know why

Another idea that I have (don't know if it works, I didn't test it), is to configure all my clients with manual DNS Servers and: by Primary - the DNS from my DC1; by secondary - the Extern DNS server. The problem here is, that I have to find a way that windows will switch from Prymary to secondary DNS immediately... I think the cache mode has to be deactivated on the client side. What do you guys think? Should I try to find a script to detect when the pc is in domain or not, or try to use this solution?

Yes! This post describes the one-liners you would probably use for setting dns. Like this one: Primary value:

netsh interface ipv4 set dns "Local Area Connection" static 192.168.0.2

For actually doing this specifically to clients outside of domain, i would suggest trying to combine netsh command with an if that checks for domain... which also is shown here:

if ((gwmi win32_computersystem).partofdomain -eq $true) {
   write-host -fore green "I am domain joined!"
} else {
   write-host -fore red "Ooops, workgroup!"
}

Also you could run the script at startup so that the clients will check at boot.

Anyways, in my head your script could look something like this:

if ((gwmi win32_computersystem).partofdomain -eq $true) {
   write-host -fore green "I am already joined"
} else {
   write-host -fore red "Not joined, using secondary dns"
   netsh interface ipv4 set dns "Local Area Connection" static <Ip-address>
} 

(Most of our answers is from these forums, wonders :p)

Best of luck, Emil

If they're configured as DHCP clients (which is the recommended configuration) then they'll be assigned whatever DNS servers the DHCP server assigns.