[Samba] declaring Bind9 DNS servers as slaves when using Samba AD/DC with BIND9_DLZ

[Rowland Penny]

On Mon, 2022-04-25 at 19:28 -0400, Vincent S. Cojot via samba wrote:
> Hi all,
> 
> I have a small isolated 'island' made of two Samba AD/DC VMs. It
> works 
> fine but is not really fault-tolerant (if one hypervisor crashes,
> every 
> Windows client will time out for 50% of DNS requests.
> 
> I was trying to setup my bind infra as DNS 'slaves' of the AD/DC
> zones but 
> I'm struggling to make it work. I suspect this might be related to
> having 
> to list my bind DNS servers as authoritative 'NS' servers for my AD
> DC 
> zones.. Here's what I have:
> 
> On a RHEL8 bind DNS server, I have declarations such as:
> zone "_msdcs.ad.lasthome.solace.krynn" IN {
>          type slave;
>          masters { 10.0.131.248; 10.0.131.249; };
>          notify yes;
>          file "zonedb/named.KRYNN_AD._msdcs";
>          allow-transfer { any; };
>          allow-query { any; };
> };
> (and the same kind of declaration for _sites, _tcp, _udp...)
> 
> On my samba, AD/DC servers, I made sure to have:
>          allow-transfer { any; };
> 
> Alas, on the BIND9 dns servers, I see this:
> 25-Apr-2022 19:16:43.809 xfer-in: info: transfer of
> '_msdcs.ad.lasthome.solace.krynn/IN' from 10.0.131.249#53: Transfer
> status: REFUSED
> 25-Apr-2022 19:16:43.809 xfer-in: info: transfer of
> '_msdcs.ad.lasthome.solace.krynn/IN' from 10.0.131.249#53: Transfer
> completed: 0 messages, 0 records, 0 bytes, 0.001 secs (0 bytes/sec)
> 
> This can be matched to these logs on the Samba AD/DC servers:
> 25-Apr-2022 16:38:01.528 notify: notice: client @0x7f0a341063f0
> 10.0.128.242#12714: received notify for zone
> '_msdcs.ad.lasthome.solace.krynn': not authoritative
> 
> so communication works but dc01 refuses the zone transfer because it
> is 
> coming from a server which is not authoritative:
> 
> Sure enough, when querying the SOA for any of these sub-domains, only
> my 
> AD/DC servers are listed:
> 
> # dig @dc00 -t SOA _msdcs.ad.lasthome.solace.krynn
> [...]
> ;; AUTHORITY SECTION:
> _msdcs.ad.lasthome.solace.krynn. 900 IN
> NS      dc01.ad.lasthome.solace.krynn.
> _msdcs.ad.lasthome.solace.krynn. 900 IN
> NS      dc00.ad.lasthome.solace.krynn.
> 
> So I have a few questions:
> 
> - How do I add my bind servers as 'proper' authoritative NS servers
> for 
> the DNS zones hosted on my AD/DC bind servers. What is the proper way
> to 
> do this? I tried using RSAT/DNS manager and enabling 'Bind
> secondaries' 
> but this did not work with Samba AD/DC.
> 
> - Is it a Bad idea to do this (add bind servers as authoritative DNS 
> servers to my AD zones)? Might it break something in the future?
> 
> All comments/ideas needed.
> 
> Thank you,
> 
> Vincent

Sorry to be late in replying, but you need 4 things:

To be running Samba >= 4.15.0

On the DC with the PDC_Emulator FSMO role, you have 'dns zone transfer
clients allow = IP_OF_THE_SLAVE_DNS_SERVER' in the smb.conf

The DC is running a Bind9 dns server with 'allow-transfer {
IP_OF_THE_SLAVE_DNS_SERVER; };' in /etc/bind/named.conf.options

Your zones in /etc/bind/named.conf.local , similar to these

zone "ad.lasthome.solace.krynn" IN {
     type slave;
     file "/var/cache/bind/named.KRYNN_AD";
     masters { 10.0.131.248; };
};

zone "_msdcs.ad.lasthome.solace.krynn" IN {
     type slave;
     file "/var/cache/bind/named.KRYNN_AD._msdcs";
     masters { 10.0.131.248; };
};

zone "0.131.10.in-addr.arpa" IN {
     type slave;
     file "/var/cache/bind/reverse.KRYNN_AD";
     masters { 10.0.131.248; };
};

Where '10.0.131.248' is the IP of the DC with the PDC_Emulator FSMO
role. It may work with multiple DC's but I haven't tested it. 

Rowland