[Samba] Authentication to Secondary Domain Controller initially fails when PDC is offline
mathias dufresne
infractory at gmail.com
Sun Nov 22 12:24:43 UTC 2015
2015-11-20 18:35 GMT+01:00 James <lingpanda101 at gmail.com>:
> On 11/20/2015 10:17 AM, mathias dufresne wrote:
>
>
>
> 2015-11-20 15:11 GMT+01:00 James <lingpanda101 at gmail.com>:
>
>> On 11/20/2015 7:40 AM, Ole Traupe wrote:
>>
>>>
>>>
>>> Am 20.11.2015 um 11:54 schrieb mathias dufresne:
>>>
>>>> Hi Ole,
>>>>
>>>> I'm still not answering your issue but I come back to speak about TTL.
>>>> Perhaps someone would be able to bring us some light on that.
>>>>
>>>> This morning I'm trying to reproduce the way I do broke my test AD
>>>> domain. This leads me to deal with SOA record (I broke my test AD seizing
>>>> FSMO roles before removing old FSMO owner, SOA was not changed during that
>>>> process and I suspect this was one of the point leading to all issues this
>>>> test domain has)
>>>>
>>>> Anyway:
>>>> samba-tool dns query m700 samba.domain.tld samba.domain.tld SOA -k yes
>>>> Name=, Records=1, Children=0
>>>> SOA: serial=1, refresh=900, retry=600, expire=86400, *minttl=3600*,
>>>> ns=m700.samba.domain.tld., email=hostmaster.samba.domain.tld.
>>>> (flags=600000f0, serial=1, *ttl=3600*)
>>>> Name=_msdcs, Records=0, Children=0
>>>> Name=_sites, Records=0, Children=1
>>>> Name=_tcp, Records=0, Children=4
>>>> Name=_udp, Records=0, Children=2
>>>> Name=DomainDnsZones, Records=0, Children=2
>>>> Name=ForestDnsZones, Records=0, Children=2
>>>> Name=m700, Records=0, Children=0
>>>>
>>>> This shows us TTL is in fact equal to minimumttl inside AD DB.
>>>>
>>>
>>> Not for me:
>>>
>>> SOA: serial=29, refresh=180, retry=600, expire=86400, minttl=180,
>>> ns=DC2.my.domain.tld., email=hostmaster.my.domain.tld. (flags=600000f0,
>>> serial=0, ttl=3600)
>>>
>>>
>>>
>>>> According to
>>>> http://stackoverflow.com/questions/20297531/meaning-of-the-five-fields-of-the-answer-section-in-dig-query
>>>> the second member of dig's answer section is TTL.
>>>>
>>>> dig -t soa samba.domain.tld
>>>> ...
>>>> samba.domain.tld. *3593* IN SOA m700.samba.domain.tld.
>>>> hostmaster.samba.domain.tld. 1 900 600 86400 3600
>>>> ...
>>>> When yesterday the same request gave the following answer:
>>>>
>>>> ...
>>>> samba.domain.tld. *1715* IN SOA DC1.samba.domain.tld. 62 900 600
>>>> 86400 3600
>>>> ...
>>>>
>>>> So I ran several that same command and each the value displayed as
>>>> second member (here 1715 or 3593) was descreased by the same amount of
>>>> second as the time between my command launchs.
>>>>
>>>> It seems this shown TTL is declared TTL (or minttl) minus the amount of
>>>> seconds since last renewal of this TTL. No idae why this behaviour. If
>>>> someone knows, I would be pleased to learn :)
>>>>
>>>
>>> Yes, I thought so. This is "remaining TTL" for you.
>>>
>>> Interestingly, for me this value is always constant and equals 1h, no
>>> matter what.
>>>
>>>
>>> ANYWAYS, I would like to approach from a different direction:
>>>
>>> If my first DC is offline, a ping on any of my domain machines takes 5+
>>> seconds to resolve. I figure that my logon problems reflect multiple such
>>> timeouts during the logon process accumulating to a total duration not
>>> accepted by the unix logon mechanism.
>>>
>>> If there would be ANY way to reduce the time (to 1 s or something) a
>>> machines waits until it finally accepts that a DNS server just won't
>>> respond and goes over to the next one... - that actually might solve the
>>> issue.
>>>
>>> Is there an option for this on unix machines?
>>>
>>> Ole
>>>
>> You can add your DC's to your hosts file. Usually your hosts file is
>> queried first, prior to DNS for resolve.
>>
>> One thing I notice a bit odd is this
>>
>> SOA: serial=29, refresh=180, retry=600, expire=86400, minttl=180,
>> *ns=DC2.my.domain.tld.*, email=hostmaster.my.domain.tld. (flags=600000f0,
>> serial=0, ttl=3600)
>>
>> Normally your name server would be the same as your DC who is SOA. Did
>> you manually change this from DC1 to DC2? What DC is your SOA?
>>
>> --
>> -James
>>
>>
>> I thought all name servers of a given zone should be declared as NS for
> they can all reply to queries.
> But on my AD there is only one NS, the SOA.
> In fact I thought the SOA was here to distinguish which NS among all NS is
> the master.
>
> With only one NS record when several DNS are present for the same zone, I
> expect only one NS will reply to every request so, according to what I had
> understood about DNS, only one DC will receive all requests from clients.
>
> If I'm right, why Samba does not add NS when a DC is joined?
>
> Today I played with fsmo seize. I haven't checked NS records until now. I
> have 2 DCs, DC1 & DC2, DC2 became new FSMO, I also modified SOA record to
> set SOA on DC2.
> Looking for NS record of my AD I have only DC1 as NS when DC2 is SOA.
>
> Ole,
>
> I would declare DC2 as NS. Then once DC1 is off, when a client would ask
> for NS list of your AD this client would receive DC1 + DC2 and would have
> more chances to send its request to DC2.
>
> Then you re-run your test with only DC2 up and running.
> Note DNS have need time to be updated if you are using others DNS servers
> between clients and AD DCs.
>
> The SOA RR identifies a primary DNS name server for the zone as the best
> source of information for the data within that zone and as a entity
> processing the updates for the zone.
>
> The NS resource record is used to notate which DNS servers are designated
> as authoritative for the zone. Listing a server in the NS RR, it becomes
> known to others as an authoritative server for the zone. This means that
> any server specified in the NS RR is to be considered an authoritative
> source by others, and is able to answer with certainty any queries made for
> names included in the zone.
>
> Much of the above was taken almost verbatim from online Microsoft tech
> documents. I don't believe that DC's create NS records by default.
>
> --
> -James
>
> As I was not confident at all neither regarding NS declaration in MS AD I
did installed 2 DCs running MS Windows 2008 R2 and then configured on them
one AD domain msad.domain.tld to check.
Both MS DCs are hosting the DNS 2 zones msad.domain.tld and
_msdcs.msad.domain.tld.
When joining the second DC dcpromo.exe complains it was not able to find
SOA for related zones.
Domain name:
msad.domain.tld
DC names / IP:
win2k8r2-01.msad.domain.tld / 10.1.1.211
win2k8r2-02.msad.domain.tld / 10.1.1.212
------------------------------------------------------------
A msad.domain.tld
------------------------------------------------------------
dig @10.1.1.212 -t A msad.domain.tld | egrep 'ANSWER |ADDITIONAL ' -A3
;; ANSWER SECTION:
msad.domain.tld. 600 IN A 10.1.1.211
msad.domain.tld. 600 IN A 10.1.1.212
dig @10.1.1.211 -t A msad.domain.tld | egrep 'ANSWER |ADDITIONAL ' -A3
;; ANSWER SECTION:
msad.domain.tld. 600 IN A 10.1.1.212
msad.domain.tld. 600 IN A 10.1.1.211
------------------------------------------------------------
------------------------------------------------------------
NS msad.domain.tld
------------------------------------------------------------
dig @10.1.1.211 -t NS msad.domain.tld | egrep 'ANSWER |ADDITIONAL ' -A3
;; ANSWER SECTION:
msad.domain.tld. 3600 IN NS win2k8r2-01.msad.domain.tld.
msad.domain.tld. 3600 IN NS win2k8r2-02.msad.domain.tld.
;; ADDITIONAL SECTION:
win2k8r2-01.msad.domain.tld. 3600 IN A 10.1.1.211
win2k8r2-02.msad.domain.tld. 3600 IN A 10.1.1.212
dig @10.1.1.212 -t NS msad.domain.tld | egrep 'ANSWER |ADDITIONAL ' -A3
;; ANSWER SECTION:
msad.domain.tld. 3600 IN NS win2k8r2-02.msad.domain.tld.
msad.domain.tld. 3600 IN NS win2k8r2-01.msad.domain.tld.
;; ADDITIONAL SECTION:
win2k8r2-02.msad.domain.tld. 3600 IN A 10.1.1.212
win2k8r2-01.msad.domain.tld. 3600 IN A 10.1.1.211
------------------------------------------------------------
------------------------------------------------------------
SAO msad.domain.tld
------------------------------------------------------------
dig @10.1.1.211 -t SOA msad.domain.tld | egrep 'ANSWER |ADDITIONAL ' -A3
;; ANSWER SECTION:
msad.domain.tld. 3600 IN SOA
win2k8r2-01.msad.domain.tld. hostmaster.msad.domain.tld. 38 900 600 86400
3600
;; ADDITIONAL SECTION:
win2k8r2-01.msad.domain.tld. 3600 IN A 10.1.1.211
dig @10.1.1.212 -t SOA msad.domain.tld | egrep 'ANSWER |ADDITIONAL ' -A3
;; ANSWER SECTION:
msad.domain.tld. 3600 IN SOA
win2k8r2-02.msad.domain.tld. hostmaster.msad.domain.tld. 38 900 600 86400
3600
;; ADDITIONAL SECTION:
win2k8r2-02.msad.domain.tld. 3600 IN A 10.1.1.212
------------------------------------------------------------
So SOA is the DC which replies. This suits the given definition as we can
modify DNS zones on each DC with DNS service running and each DC can
propagate modifications.
NS are all declared as they are authoritative name servers, this also suits
given definition: each DC can reply DNS request with certainty because of
replication.
This domain as no client, it was built only for testing that.
It seems there is some round-robin stuff on SN and A RR: running several
times same request on same DC change the answer for records A and NS:
dig @10.1.1.211 -t A msad.domain.tld | egrep 'ANSWER |ADDITIONAL ' -A3
;; ANSWER SECTION:
msad.domain.tld. 600 IN A 10.1.1.211
msad.domain.tld. 600 IN A 10.1.1.212
dig @10.1.1.211 -t A msad.domain.tld | egrep 'ANSWER |ADDITIONAL ' -A3
;; ANSWER SECTION:
msad.domain.tld. 600 IN A 10.1.1.212
msad.domain.tld. 600 IN A 10.1.1.211
Once more: I'm not an expert. I'm just sending here my thoughts, trying to
understand.
Best regards all and have a nice weekend,
mathias
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