[Samba] Secondary DNS on active directory possible?

[Markus Mueller]

Hi Samba community

first post on this list, so apologies in advance for mistakes.

I run a Samba AD domain (let's call it myAD.mydomain.net) with DLZ DNS 
backend (Ubuntu 20.04, vanilla Samba install) which I migrated from an 
NT-style domain. Not all machines in my network participate in the AD 
(some Linux only machines and guests), which is why I have a separate 
'master' DHCPD/bind9 server (let's call it master.mydomain.net) serving 
zone mydomain.net. The AD host (nameserver.myAD.mydomain.net) serves 
zone myAD.mydomain.net.

Ideally, I would like to have the Samba-DNS serving the requests from 
myAD.mydomain.net and the DHCPD/bind9 machine serving mydomain.net 
(which they do). But: the samba AD should forward all requests for 
mydomain.net to the master nameserver (which it does not, even though I 
set the dns forwarder to master.mydomain.net in smb.conf). It should be 
possible (in my opinion) by creating a secondary DNS zone on the Samba 
AD (nameserver.myAD.mydomain.net). But that doesn't seem allowed. 
samba-tool allows me to create that zone, but I couldn't figure out how 
to do the slave config (e.g. setting the master server). The Microsoft 
DNS tool does not allow me to create a secondary zone at all.

Why do I try so complicated? My general nameserver failed recently from 
a segmentation fault and my whole intranet went down (because my dhcpd 
relies on client identification via DNS, mainly for historical reasons). 
I would like to have a backup nameserver, but I prefer not to install 
yet another instance.

Cheers
Markus