Exchange - Domain Controller crashed, no failover?


I have two DC and one exchange server:
Dc-1 Dc-2  exchange-srv

Exchanger server is configured like that:
This weekend our dc-2 crashed with thoses errors :

Then users coulnt log on their mailbox, I found this error in transport log:

2015-08-09T12:08:27.867Z,08D25B65394B02C0,MapiSubmission,f1ca1ebc-6f44-4424-a060-15fb0c16446a,>,"Failed; HResult: 1090519040; DiagnosticInfo: Stage:LoadItem, SmtpResponse:432-4.2.0 STOREDRV.Submit.Exception:StorageTransientException.ADPossibleOperationException.DirectoryOperationException; Failed to process message due to a transient exception with message There was a problem accessing Active Directory. Check your network connections and try again. ADPossibleOperationException: Active Directory operation failed on DC-***-02.*********.com. This error could have been caused by user input or by the Active Directory server being unavailable. Please retry at a later time. Additional information: Additional information: The directory service encountered an unknown failure."

2015-08-09T12:08:27.867Z,08D25B65394B02C0,MapiSubmission,f1ca1ebc-6f44-4424-a060-15fb0c16446a,-,RegularSubmissions: 0 ShadowSubmissions: 0 Bytes: 0 Recipients: 0 Failures: 1 ReachedLimit: False Idle: False

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When i fixed DC-02 (with one reboot), problem resolved.

Can you explain me what is this error? The link between exchange and this DC-02... Why exchange didnt use a failover on DC-01 when he couldnt logged users?

Thanks in advance
CLR BenjaminAsked:
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Lee W, MVPTechnology and Business Process AdvisorCommented:
Are both DCs Global Catalogs?  Exchange Relies on the global catalog servers.  It also picks one and sticks with it.  If it goes down, it will try to find another, but only after at least 30 minutes.  Have you run DCDIAG /C /E /V to check the health of AD and ensure everything is ok on both DCs?
CLR BenjaminAuthor Commented:
Yes, both are GC.

I will launch this diag to night, I will drop the results later.

Will SzymkowskiSenior Solution ArchitectCommented:
You need to make sure that in your DNS configuration for the Exchange server that you have both DC1 and DC2 in there for Primary and Secondary DNS.

Once you have setup this on the network adapters on your Exchange servers the Exchange will continue to work.

This is assuming that your DC's and Exchange server are in the same active directory site.

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AmitIT ArchitectCommented:
Which server was holding FSMO?
CLR BenjaminAuthor Commented:
DC1 & DC2 are well configured in the network adapter (in the field DNS1 and 2).

DC's and Exchange server are in the same AD.

C:\Users\*********>netdom query fsmo /domain *******.com
Contrôleur de schéma        DC-***-01.*******.com
Maître des noms de domaine  DC-***-01.*******.com
Contrôleur domaine princip. DC-***-02.*******.com
Gestionnaire du pool RID    DC-***-02.*******.com
Maître d'infrastructure     DC-***-02.*******.com
L'opération s'est bien déroulée.

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AmitIT ArchitectCommented:
Root cause for your issue is fsmo was present on dc2, that is why your user was not able to login. It is dc issue not exchange issue. If you see PDC role is on dc2 which is core role required. You need to make sure fsmo are up on other server.

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Will SzymkowskiSenior Solution ArchitectCommented:
Exchange will continue to operate without the PDC online for a period of time, however you stated that it was over night when this failed. So if it was out for an EXTENDED period of time (which it was) then this would be the issue.

If the PDC was offline for a short time then this would not affect Exchange.

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