[Twisted-Python] Twisted.Names question

[Rudy Schockaert]

How can I return a referral to another server when I cannot resolve the 
query myself?

My setup would be as follows:
I have a Twisted Names master server and a  number of Twisted Names 
slave servers.
The master server is only to be used by the DNS clients when the slave 
server is not available.
The Twisted Names servers can only answer very specific queries. All 
other responses have to come from the Internet.

My idea is to configure the clients as follows:

Primary DNS server: Twisted Names Slave
Secondary DNS server: Twisted Names Master
Tertiary DNS server: Internet DNS server

I have to configure the Twisted Names Master as secondary for 
resilience, but the client should only call him when the the Twisted 
Names Slave doesn't respond and not when it doesn't have the answer.

Rudy