[Samba] Domain member cannot authenticate when first domain controller is down

Wed Mar 3 22:27:03 UTC 2021

On 3/3/21 2:42 PM, Kris Lou via samba wrote:
> Domain member krb.conf (mostly stolen from Jason's ticket above, but you
> get the point. : https://bugzilla.samba.org/show_bug.cgi?id=14597)
>
> [libdefaults]
>   default_realm = AD.SAMDOM
>   dns_lookup_realm = false
>   dns_lookup_kdc = false <----------------------
>   rdns = false
>   forwardable = true
>   renew_lifetime = 7d
>
> [realms] <---------------
>   AD.SAMDOM = {
>    kdc = ip.add.re.ss1:88
>    kdc = ip.add.re.ss2:88
>   }
>
> When we tested this a while ago (same issues, with ... sssd, so take with a
> grain of salt), the above was supposed to specify the KDC instead of
> relying on DNS.  I hope the syntax is right, I haven't checked the man
> pages in a while.
>
> Also, Verifying kerberos SRV records:
> https://wiki.samba.org/index.php/Setting_up_Samba_as_an_Active_Directory_Domain_Controller#Verifying_DNS
>
> They should exist for each DC.
Kris,

I was wondering if these wiki tests were what you had in mind.  Both 
DC's passed those tests during the building process and still do. The 
following results are from DC2.

_ldap._tcp.workgroup.realm.tld has SRV record 0 100 389 dc1.workgroup.realm.tld.
_ldap._tcp.workgroup.realm.tld has SRV record 0 100 389 dc2.workgroup.realm.tld.

_kerberos._udp.workgroup.realm.tld has SRV record 0 100 88 dc1.workgroup.realm.tld.
_kerberos._udp.workgroup.realm.tld has SRV record 0 100 88 dc2.workgroup.realm.tld.

dc2.workgroup.realm.tld has address 192.168.x.y

DC1 has the same results, except that it reverses the order of the DC's 
for the ldap SRV query and resolves to its own address for the A query; 
still, both are correctly listed.

dc1.workgroup.realm.tld has address 192.168.x.z

Experimenting with the resolv.conf options that Louis provided may have 
helped slightly, but a "getent passwd" that I timed took 40 seconds, 
something that is instantaneous when DC1 is online.  (This is not a 
large domain.)  An SSH login was similarly long.

I will experiment with the krb5.conf options that you (and Jason) 
provided to see if there is any benefit.  I know Rowland teaches only 3 
lines are needed in krb5.conf, so I wonder what his opinion of these 
modifications is.

Thanks,
Dale

>
>
> Kris Lou
> klou at themusiclink.net
>
>
> On Wed, Mar 3, 2021 at 11:08 AM Dale <samba at txschroeder.family> wrote:
>
>> On 3/3/21 9:58 AM, L.P.H. van Belle via samba wrote:
>>
>> Check the following.
>>
>> dig ns $(hostname -d)
>> You should see all the AD-DC servers, if not add the NS record of the missing ones, then when thats done.
>>
>> try these settings and test what works best for you, add in /etc/resolv.conf
>>
>> options timeout:3
>> options attempts:2
>> options rotate
>>
>> (see : man resolv.conf what these do)
>>
>> in smb.conf..
>> Try setting :
>>
>> cache directory = /var/cache/samba
>> (do check if the folder exists. )
>>
>> these parts would be the first one's i would look into.
>>
>> I hope this can help you.
>>
>> Greetz,
>>
>> Louis
>>
>> *@ Louis*
>>
>> The dig command returns the correct results, and the cache directory
>> setting already matches what you had suggested.
>>
>> I will experiment with the resolv.conf options that you mentioned.
>>
>> *@ Jason*
>>
>> I have requested a bugzilla account in order to add a "me too" to your bug
>> report.  If what I'm experiencing is not identical, it is most certainly
>> similar.
>>
>> *@ Kris*
>>
>> I'll need some direction for this -
>>
>> <KL> "Also, are the _kerberos SRV records correct for DC2?"
>>
>>
>> Where/How do I find this, and what *are* the expected values?
>>
>> Thanks to all for the suggestions.
>>
>> Dale
>>
>> -----Oorspronkelijk bericht-----
>> Van: samba [mailto:samba-bounces at lists.samba.org <samba-bounces at lists.samba.org>] Namens Dale via samba
>> Verzonden: woensdag 3 maart 2021 16:25
>> Aan: Josh T; Roy Eastwood; samba at lists.samba.org
>> Onderwerp: Re: [Samba] Domain member cannot authenticate when first domain
>> controller is down
>>
>> Josh, I don't have the answer to your question, but if you ever figure
>> it out, I would like to know the answer, too.
>>
>> The 2nd DC that I built has been of very little use.  While building, it
>> passed all the tests in the wiki.  After building, I found some DNS
>> entries that were not created during the join. Rowland kindly helped me
>> add and/or edit the affected entries, and I hoped for better results.
>> However, it was not to be.  If the 1st DC is removed from the network,
>> any kind of login or getent is interminably long or times out.  So,
>> while I easily see the theoretical value of having multiple DC's, I'm
>> having trouble seeing the actual, practical benefit of having them.
>> There is no instant failover, and often times, there is complete failure
>> of necessary AD functions.  While it's certainly possible the problem
>> could be me, I cannot troubleshoot what the problem is.
>>
>> Dale
>>
>>
>> On 3/1/21 6:25 PM, Josh T via samba wrote:
>>
>> Further fiddling with this has shown something strange. If I enter my
>>
>> username and password in an attempt to authenticate a domain user, it will
>> take 60+ seconds for it to fail to log in. However, during said 60+
>> seconds, if I log in via SSH as a non-domain user, then the domain user
>> login succeeds. What could cause that?
>>
>> ________________________________
>> From: Roy Eastwood <spindles7 at gmail.com> <spindles7 at gmail.com>
>> Sent: Saturday, February 27, 2021 1:27 AM
>> To: 'Josh T' <c3h4ohcooh3 at hotmail.com> <c3h4ohcooh3 at hotmail.com>; samba at lists.samba.org
>>
>> <samba at lists.samba.org> <samba at lists.samba.org>
>>
>> Subject: Re: [Samba] Domain member cannot authenticate when first domain
>>
>> controller is down
>>
>> On 27 February 2021 03:35 Josh T wrote:
>>
>> //Problem:
>> I am unable to authenticate a domain user on a Samba domain member
>>
>> while the
>>
>> first Samba directory controller DC1 is powered off and the second
>>
>> Samba
>>
>> directory controller DC2 is powered on.
>>
>> While DC1 is powered on, I can log in as a domain user with no
>>
>> problems. While
>>
>> DC1 is powered off, attempting to log in usually results in waiting 60+
>>
>> seconds
>>
>> followed by a login failure message. If I had already logged in prior
>>
>> to
>>
>> powering
>>
>> off DC1, then I can see the same long delay and authentication failures
>>
>> when
>>
>> entering my sudo password. Intermittently I can sometimes manage to log
>>
>> in
>>
>> while DC1 is powered off, but there is still the 60+ second delay; I
>>
>> haven't
>>
>> been
>>
>> able to link this intermittent behavior to any of my own
>>
>> troubleshooting
>>
>> actions.
>>
>> In any case, a 60+ second delay is undesirable.
>>
>> //Environment description:
>> The first Samba domain controller DC1 was created following these
>>
>> instructions
>>
>> on the Samba wiki:
>>
>>
>> https://wiki.samba.org/index.php/Setting_up_Samba_as_an_Active_Directory_
>>
>> Domain_Controller
>> It was provisioned using the command "samba-tool domain provision --
>>
>> use-
>>
>> rfc2307 --interactive".
>> The BIND9_DLZ DNS backend was selected during provisioning.
>> Samba version 4.11.6-Ubuntu was installed on DC1 using the apt command.
>>
>> The second Samba domain controller DC2 was created following these
>> instructions on the Samba wiki:
>>
>>
>> https://wiki.samba.org/index.php/Joining_a_Samba_DC_to_an_Existing_Active
>>
>> _Directory
>> It was joined using the command "samba-tool domain join my.domain.tld -
>>
>> -dns-
>>
>> backend=BIND9_DLZ --option='idmap_ldb:use rfc2307 = yes'".
>>
>> The above is missing the letters  "DC" in the command line.   This may
>>
>> be the
>>
>> issue.
>>
>> HTH
>>
>> Roy
>>
>>
>>
>>
>>
>> --
>> To unsubscribe from this list go to the following URL and read the
>> instructions:  https://lists.samba.org/mailman/options/samba
>>
>>
>>