[Samba] Recurrent DNS issues after DC loss

lingpanda101 lingpanda101 at gmail.com
Wed Jun 6 12:44:50 UTC 2018

On 6/6/2018 4:54 AM, Ole Traupe via samba wrote:
> On 05.06.2018 20:39, lingpanda101 wrote:
>> On 6/5/2018 2:11 PM, Ole Traupe via samba wrote:
>>> Hi list,
>>> I have a domain in production on two sites (subnets, via "Sites and 
>>> Services") with originally two DCs. One went down due to HDD (-> old 
>>> hardware) error. Now, occasionally, clients cant access/find the 
>>> file server (domain member). This does not occur on all clients at 
>>> the same time, however, so I am rather sure it is not the file 
>>> server itself, but a DNS problem.
>>> I couldn't find anything diagnostic in the logs. Default log level 
>>> was not informative, I think, while log level 10 I just could not 
>>> handle/analyze properly.
>>> Can someone recommend a log level? Should I look on the DC or on the 
>>> file server?
>>> Do I have to remove the offline DC completely from DNS and Sites and 
>>> Services for this mess to stop?
>>> I appreciate any advice.
>>> Cheers,
>>> Ole
>> Ole,
>>     If you haven't already removed the dead DC from your network you 
>> should do that first.
>> https://wiki.samba.org/index.php/Demoting_a_Samba_AD_DC
>> Your clients DNS may still be pointing to the offline DC causing look 
>> up delays. Also did you have your DC's pointing to themselves for DNS 
>> or each other?
> ** SNIP **
> Actually, the DCs (resolv.conf) were pointing to each other initially, 
> and I think that was at least one root of the evil. I think this 
> advice in the Samba wiki actually is rather bad (and unnecessary with 
> Samba, as has been pointed out, before?).
Using Bind I find it's necessary to point the DC to itself. I had no 
issues pointing to another DC with the internal DNS. The Wiki actually 
mentions best practice for a multi DC environment as it relates to a 
Windows setup. I do think it's unnecessary with Samba however.
> Regarding demoting the dead DC: My Samba version is rather old 
> (4.2.5). The problem is that I chose the uid/gid scopes unwisely. And 
> I read on some patch notes that I can't update anymore, because newer 
> versions of Samba actually require those scopes to be set in a very 
> specific way. So perhaps demoting via the newly available method is 
> not an option here.
Can you repair or replace the dead DC with a current Samba version? Join 
then transfer the FSMO roles? I would advise not using the same hostname.
> What I can think of is:
> - removing the dead DC from the clients DNS config, of course
> - removing it from AD DNS
> - removing it from AD Sites and Services
> - and removing it from AD Users and Computers
Yes to all the above. The key is to remove all service records in DNS 
that reference the bad DC. It's easier to use RSAT for this. Make sure 
you remove all NTDS connections as well that reference the dead DC. 
Reference the Wiki as it does a good job displaying an example of 
running '# samba-tool domain demote --remove-other-dead-server=DC2'. It 
shows all that seems necessary.
> What else does the Samba script for demoting a DC do? Can I do that 
> manually, too? I repeat: it was not the FSMO role holder.
I don't know.
> Thanks again for any advice!
> Ole



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