[Samba] Authentication to Secondary Domain Controller initially fails when PDC is offline

mathias dufresne infractory at gmail.com
Fri Nov 27 15:24:09 UTC 2015

2015-11-27 15:49 GMT+01:00 Rowland Penny <rowlandpenny241155 at gmail.com>:

> On 27/11/15 14:30, James wrote:
>> On 11/27/2015 9:16 AM, Rowland Penny wrote:
>>> On 27/11/15 13:23, James wrote:
>>>> On 11/26/2015 11:12 AM, Ole Traupe wrote:
>>>>> Then you re-run your test with only DC2 up and running.
>>>>>>> Note DNS have need time to be updated if you are using others DNS
>>>>>>> servers between clients and AD DCs.
>>>>>> The SOA RR identifies a primary DNS name server for the zone as the
>>>>>> best source of information for the data within that zone and as a entity
>>>>>> processing the updates for the zone.
>>>>>> The NS resource record is used to notate which DNS servers are
>>>>>> designated as authoritative for the zone. Listing a server in the NS RR, it
>>>>>> becomes known to others as an authoritative server for the zone. This means
>>>>>> that any server specified in the NS RR is to be considered an authoritative
>>>>>> source by others, and is able to answer with certainty any queries made for
>>>>>> names included in the zone.
>>>>>> Much of the above was taken almost verbatim from online Microsoft
>>>>>> tech documents.  I don't believe that DC's create NS records by default.
>>>>> You mean Samba DCs or DCs in general?
>>>>> I am not sure I understand the above. Do you suggest to create another
>>>>> NS record for the Second_DC, or not to?
>>>>> In the resolv.conf on my member servers both DCs are listed as DNS
>>>>> servers. I like to think that the member servers eventually ask the second
>>>>> DNS server, if the first won't respond. This seems to be reflected by ping
>>>>> taking more than 5 s for the first packet to arrive.
>>>>> BUT what does the second DNS server (Second_DC) reply? Which logon
>>>>> server does it announce?
>>>>> DNS can be very confusing. You do not need to create a NS record for
>>>> your second DC if the zone is directory integrated. By default the DC is
>>>> authoritative for that zone.
>>> Probably with windows it is, but not with Samba AD, you only get one NS
>>> and one SOA. The only authoritative Samba AD DC is the first one, when you
>>> join a second DC, it runs the same code that created the SOA during the
>>> first DCs provision and because the SOA already exists, it fails.
>>> Rowland
>>> Yikes! Are you saying DC's with directory integrated zones are not
>> authoritative for them? That means a NS record needs to be created manually
>> for each DC added.
> Yes, that's about the size of it. no matter how many DCs you join, you
> only have one NS, the original DC.
> I have been trying to alter the code, but I am struggling to get another
> NS record added during the join, it doesn't help that I have no idea what a
> windows DC SOA record looks like, does each DC have a separate SOA record?
> or is it like the Samba SOA record and there is only one with multiple NS
> records?
Yes each Windows has SOA record. In fact I expect there is no SOA record
really on MS AD. I expect SOA management is something like when a DC
receive request for SOA it replies "I am SOA".
On MS AD all DC have a NS record. My second mail about that thread from
Sunday the 22nd of November is showing different DNS queries I did on MS AD
domain (a 2008 r2 domain with only 2 DC, Microsoft DC).

Finally I would look into samba_dnsupdate to add creation of NS record. I
expect this tool is run when samba starts.
Unfortunately I did not find the right option to add to samba_dnsupdate for
it really creates DNS entries. Even with kerberos ticket already created
before running that command. I received a mail recently about another Samba
user using internal DNS for his AD hosted by Samba. This person was facing
same issue has me (missing DNS entries, samba_dnsupdate not adding
entries). To workaround that issue he modified samba_dnsupdate and he
commented that line (line 413):

Doing that samba_dnsupdate does not remove tmp file. This tmp file contains
nsupdate commands which are launched by samba_dnsupdate.
Finally he uses these nsupdate commands from tmp files without -g option
and he's DNS entries are now created.
I must say I did yet try that process.

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