In trying to improve my DNS knowledge, I've got a couple of questions about the principles behind DNS. Both relate to what happens when you query a DNS server for an address which it doesn't hold itself.

1. If the nameserver for sub.mydomain.com gets a request for a host in mydomain.com, will it always refer that right up to the root servers or does it have a way of passing queries up the tree without jumping right to the top?

2. On the internet, queries for servers outside the knowledge of the local server get passed up to the root servers. Is it possible to set up a private network, not connected to the internet at all, with its own root servers?

Thanks,

Question 1
You can program forwarders in to your DNS servers. This tells the DNS server to pass unknown requests directly to that server instead of going to the root servers.

Question 2
Using forwarders, you can have a large network with domains and sub domains and no connection to the Internet and provide your own DNS services for that network.

Of course, thanks. I'd read about forwarders in a slightly different context and hadn't put it together.

So would you configure all your DNS servers to have, as forwarders, the top level DNS server(s) within your organisation; to minimise external traffic?

Yes, you could do it that way. It depends on how large an orginization you have, how large a geographic area it covers and how many DNS servers you have.