I have a two-controllers AD domain, and all domain-joined PCs have their addresses as primary and secondary DNS servers.
I wonder if I should configure a tertiary public DNS. The reasoning is that many PCs are located in smaller remote networks and they reach both domain controllers via a central VPN tunnel. If the VPN tunnel goes down, both DCs would be unavailable and the remote PCs will be unable to resolve any addresses, preventing them for surfing the internet/checking email/etc.
Adding a DC in each network is out of question (they are of 5/10 PCs), and the same can be said about creating a direct VPN tunnel from the remote network to the secondary DC site (due to hardware capacity).
A tertiary, public DNS server would prevent this, but I wonder if it can cause problems (ie: if it is, for some reason, selected as the preferred DNS, the PC would be "disconnected" from the domain).
So: it is ok to use a tertiary public DNS on a domain-joined PC, or it will cause problems? Anything to be aware of?