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Re: [Samba] Recurrent DNS issues after DC loss




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




-JAMES

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