Event 611, Directory Synchronization | Password hash synchronization failed | Version 2.2.1.0

Question

Environment is a multi-connector site. Only 2 of the connectors are getting this error. One of the connectors last sync was a few days ago. While the other one has never synced.

Password hash synchronization failed for domain: OMITTED_DOMAIN, domain controller hostname: <not available>, domain controller IP address: <not available>. Details: 
Microsoft.Online.PasswordSynchronization.SynchronizationManagerException: Unable to open connection to domain: OMITTED_DOMAIN. Error: An exception occurred while attempting to resolve the hostname/ipaddress OMITTED_IP. ---> Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsCommunicationException: An exception occurred while attempting to resolve the hostname/ipaddress OMITTED_IP. ---> System.Net.Sockets.SocketException: No such host is known
   at System.Net.Dns.InternalGetHostByAddress(IPAddress address, Boolean includeIPv6)
   at System.Net.Dns.GetHostEntry(String hostNameOrAddress)
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.ResolveSourceHostname()
   --- End of inner exception stack trace ---
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.ResolveSourceHostname()
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.CreateSourceDomainInformation()
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.EstablishConnection()
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.Connect()
   at Microsoft.Online.PasswordSynchronization.RetryUtility.<>c__DisplayClass2_0.<ExecuteWithRetry>b__0()
   at Microsoft.Online.PasswordSynchronization.RetryUtility.ExecuteWithRetry[T](Func`1 operation, Func`1 shouldAbort, RetryPolicyHandler retryPolicy)
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.OpenConnection(IDrsConnection connection)
   --- End of inner exception stack trace ---
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.OpenConnection(IDrsConnection connection)
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.CreateConnection()
   at Microsoft.Online.PasswordSynchronization.DeltaSynchronizationTask.SynchronizeCredentialsToCloud()
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.SynchronizeSecrets()
   at Microsoft.Online.PasswordSynchronization.SynchronizationExecutionContext.SynchronizeDomain()
   at Microsoft.Online.PasswordSynchronization.SynchronizationManager.SynchronizeDomain(SynchronizationExecutionContext syncExecutionContext)
Microsoft.Online.PasswordSynchronization.SynchronizationManagerException: Unable to open connection to domain: OMITTED_DOMAIN. Error: An exception occurred while attempting to resolve the hostname/ipaddress OMITTED_IP. ---> Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsCommunicationException: An exception occurred while attempting to resolve the hostname/ipaddress OMITTED_IP. ---> System.Net.Sockets.SocketException: No such host is known
   at System.Net.Dns.InternalGetHostByAddress(IPAddress address, Boolean includeIPv6)
   at System.Net.Dns.GetHostEntry(String hostNameOrAddress)
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.ResolveSourceHostname()
   --- End of inner exception stack trace ---
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.ResolveSourceHostname()
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.CreateSourceDomainInformation()
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.EstablishConnection()
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.Connect()
   at Microsoft.Online.PasswordSynchronization.RetryUtility.<>c__DisplayClass2_0.<ExecuteWithRetry>b__0()
   at Microsoft.Online.PasswordSynchronization.RetryUtility.ExecuteWithRetry[T](Func`1 operation, Func`1 shouldAbort, RetryPolicyHandler retryPolicy)
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.OpenConnection(IDrsConnection connection)
   --- End of inner exception stack trace ---
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.OpenConnection(IDrsConnection connection)
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.CreateConnection()
   at Microsoft.Online.PasswordSynchronization.DeltaSynchronizationTask.SynchronizeCredentialsToCloud()
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.SynchronizeSecrets()
   at Microsoft.Online.PasswordSynchronization.SynchronizationExecutionContext.SynchronizeDomain()
   at Microsoft.Online.PasswordSynchronization.SynchronizationManager.SynchronizeDomain(SynchronizationExecutionContext syncExecutionContext)
Microsoft.Online.PasswordSynchronization.SynchronizationManagerException: Unable to open connection to domain: OMITTED_DOMAIN. Error: An exception occurred while attempting to resolve the hostname/ipaddress OMITTED_IP. ---> Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsCommunicationException: An exception occurred while attempting to resolve the hostname/ipaddress OMITTED_IP. ---> System.Net.Sockets.SocketException: No such host is known
   at System.Net.Dns.InternalGetHostByAddress(IPAddress address, Boolean includeIPv6)
   at System.Net.Dns.GetHostEntry(String hostNameOrAddress)
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.ResolveSourceHostname()
   --- End of inner exception stack trace ---
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.ResolveSourceHostname()
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.CreateSourceDomainInformation()
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.EstablishConnection()
   at Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.Connect()
   at Microsoft.Online.PasswordSynchronization.RetryUtility.<>c__DisplayClass2_0.<ExecuteWithRetry>b__0()
   at Microsoft.Online.PasswordSynchronization.RetryUtility.ExecuteWithRetry[T](Func`1 operation, Func`1 shouldAbort, RetryPolicyHandler retryPolicy)
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.OpenConnection(IDrsConnection connection)
   --- End of inner exception stack trace ---
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.OpenConnection(IDrsConnection connection)
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.CreateConnection()
   at Microsoft.Online.PasswordSynchronization.DeltaSynchronizationTask.SynchronizeCredentialsToCloud()
   at Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.SynchronizeSecrets()
   at Microsoft.Online.PasswordSynchronization.SynchronizationExecutionContext.SynchronizeDomain()
   at Microsoft.Online.PasswordSynchronization.SynchronizationManager.SynchronizeDomain(SynchronizationExecutionContext syncExecutionContext)
.

<forest-info>
  <partition-name>OMITTED_DOMAIN</partition-name>
  <connector-id>OMITTED_ID</connector-id>
</forest-info>

Answer 1

Hello @KAM9774 , in this case the Password hash synchronization failed for domain error is being caused by DNS issues. Please follow steps detailed in Windows Server DNS troubleshooting guidance to identify and fix common DNS issues.

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