[Samba] which DNS backend ?

Rowland penny rpenny at samba.org
Mon Feb 29 09:10:13 UTC 2016

On 28/02/16 23:05, Reindl Harald wrote:
> Am 28.02.2016 um 23:54 schrieb Rowland penny:
>> On 28/02/16 22:42, Reindl Harald wrote:
>>> Am 28.02.2016 um 23:10 schrieb Rowland penny:
>>>> On 28/02/16 21:56, Reindl Harald wrote:
>>>>> Am 28.02.2016 um 22:22 schrieb John Gardeniers:
>>>>>> Thanks Rowland. Perhaps because I expected these basic issues to 
>>>>>> have
>>>>>> been resolved long ago I never thought to check the SOA records.
>>>>>> You are
>>>>>> perfectly correct - the second DC is not listed
>>>>> since when is more than one NS listed in the SOA?
>>>>> http://rscott.org/dns/soa.html
>>>>> MNAME ("Primary NS") - This entry is the domain name of the name
>>>>> server that was the original source of the data (this entry MUST be
>>>>> your primary nameserver). This is your primary nameserver, and 
>>>>> MUST be
>>>>> the one and only server that you ever update. You must not update the
>>>>> secondary server(s) -- they will update automatically, based on this
>>>>> the SOA record. Problem? This should be a fully qualified domain 
>>>>> name .
>>>> OK, I see where you are coming from, but, this is referring to a 
>>>> normal
>>>> dns server that replicates to other secondary dns servers. AD dns 
>>>> works
>>>> a little differently, all AD dns servers replicate dns records to each
>>>> other and each AD DC is supposed to be authoritative for the dns 
>>>> domain,
>>>> this does not happen if your first DC goes down when you are using the
>>>> internal dns server. As an aside, my first DC shutdown for some 
>>>> reason,
>>>> I didn't notice for a couple of hours, until I tried to 'ssh' into 
>>>> it, I
>>>> didn't notice because *everything* else just kept working on my
>>>> second DC
>>> well, that's not the business of the SOA record
>>> it's a matter of NS-records
>> If you only have one Authoritative nameserver (which is what you have
>> with the internal dns) and it disappears, then you don't have *anything*
>> that will respond to a request for info about AD dns domain
> sorry, but that's not a matter of SOA
> all your NS-records are authoritative, no matter if the yare master or
> slave, the format of the SOA record is pretty clear
> https://support.dnsimple.com/articles/soa-record/
> ns1.dnsimple.com admin.dnsimple.com 2013022001 86400 7200 604800 300
> nothing will change the SOA format because it's defined far away from 
> samba and the implementation https://www.ietf.org/rfc/rfc1912.txt
> otherwise show me how you imageine a SOA record listing more than one 
> nameserver would look like when the second filed is by defintion the 
> admin contact

Everything you say is valid except for when it comes to AD dns.
When you want data from a zone, you start with the SOA record, you ask 
'who holds the records for this zone?', it replies with the nameserver 
that holds the zone records. OK so far ?

Only problem is that with AD, *every* DC that runs a dns server holds 
the zone records. Now if you have only one NS record in the SOA (or if 
only one NS record is returned, like the internal dns server does), then 
only one DC will be asked for the zone records, if this DC is down, you 
don't have a nameserver to ask!

Every windows DC that runs a dns server is authoritative for the dns 
domain and has a SOA record. The only way I have found of doing this 
with a Samba DC, is to use Bind9 and add the second DCs NS record to the 
SOA, this SOA is stored in AD.


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