How do I make Zeroshell query another DNS server, when the subdomain for an own master domain is not found?

Question

I use Zeroshell, and there, the DNS service of it.

Now, we have servers, that need to be accessible from internal servers. Problem is, some subdomains exist in the outside world, so it needs to query another server for those subdomains. How do I make Zeroshell query another server for subdomains that are not known to itself?

Zeroshell uses bind9, so configurations apply.

Answer 1

A few questions for you;

does the subdomain exist in both realms?

Do internal servers need access to both internal and external realms?

What DNS application are you running on the external domains and do you have administrative rights to the external servers?