[Samba] which DNS backend ?

Allen Chen achen at harbourfrontcentre.com
Sat Mar 5 14:39:53 UTC 2016

On 3/5/2016 4:27 AM, Rowland penny wrote:
> On 05/03/16 04:54, Allen Chen wrote:
>> On 2/29/2016 4:10 AM, Rowland penny wrote:
>>> 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.
>>> Rowland
>> When I read this discussion about DNS, I got my big problem fixed 
>> which involves two DCs(I use samba internal DNS).
>> I want to share my experience with you:
>> The big problem is when the first DC is down, users cannot log in to 
>> win7 machine, while the second DC is still working.
>> The problem is that the internal DNS doesn't have a NS record for the 
>> second DC. After I use windows tool to add this record, shutdown the 
>> first DC and users can log in without any  issue.
>> The SOA record is set up correctly when I build the DC. So nothing is 
>> wrong with the SOA stuff in samba internal DNS.
>> Allen
> Now that is interesting, when I tested, even when you added the second 
> NS record to the SOA, you only got one NS record (the first DC) and 
> you couldn't login anywhere if the first DC went down.
> What version of Samba are you using ?
> Rowland
It is Samba 4.1.13 on CentOS 6.2 32bit for both main site and remote 
site connected via OpenVPN.
I get two NS records from any Linux system using this command:
# dig NS mydomain.com @dc1
# dig NS mydomain.com @dc2

What I understand is:
1. SOA record is used for zone transfer, and samba uses its on way to 
manage zone data.
2. in samba world, SOA is not that important, but you have to make sure 
the same SOA record is set up across all DCs.
     This makes sense when the first DC is dead, the SOA still points to 
dead one, and for new added DC you make sure you have a NS record for 
the new one.
     This will guarantee the name resolution is still working across all 
DCs. and it has nothing to do with SOA. right?
     Though I don't know if Samba DC uses SOA record or not. Maybe some 
one from dev can answer this.
3. I use windows tool to manage site settings to keep remote site log in 
to remote dc, and main site log in to main dc.
4. Windows clients use my company's DNS servers, and these DNS servers 
forward AD DC domain query to my two DCs.
5. I use samba internal DNS


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