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Replication error 1256 The remote system is not available

Published: December 21, 2011

Updated: March 1, 2012

Applies To: Windows Server 2000, Windows Server 2003, Windows Server 2008, Windows Server 2008 R2

This article describes the symptoms, cause, and resolution steps for cases when Active Directory replication fails with error 1256: The remote system is not available.

  1. The DCDIAG reports that the Active Directory Replications test has failed with error 1256: "The remote system is not available."

    Starting test: Replications
    [Replications Check, <Destination DC>] A recent replication attempt failed:
    From <source DC> to <destination DC>
    Naming Context: <directory partition DN path>
    The replication generated an error (1256):The remote system is not available. For information about network troubleshooting, see Windows Help.
    The failure occurred at <date> <time>
    The last success occurred at <date> <time>
    
    
  2. REPADMIN.EXE reports that a replication attempt has failed with status 1256.

    REPADMIN commands that commonly cite the 1256 status include but are not limited to:

     

    • REPADMIN /REPLSUM

    • REPADMIN /SHOWREPL

    • REPADMIN /SHOWREPS

    • REPADMIN /FAILCACHE

    Sample output from "REPADMIN /SHOWREPS" depicting inbound replication from LonEMEADC to LonContosoDC failing with "The remote system is not available" error is shown below:

    Repadmin: running command /showrepl against full DC localhost
    London\LONCONTOSODC
    DSA Options: IS_GC 
    Site Options: (none)
    DSA object GUID: a29bbfda-8425-4cb9-9c66-8e07d505a5c6
    DSA invocationID: d58a6322-6a28-4708-82d3-53b7dcc13c1a
    ==== INBOUND NEIGHBORS ======================================
    <snip>
    DC=ForestDnsZones,DC=Contoso,DC=com
    London\LONEMEADC via RPC
    DSA object GUID: cd691606-63d1-4cc8-b77a-055674ba569d
    Last attempt @ 2010-06-10 17:35:46 failed, result 1256 (0x4e8):The remote system is not available. For information about network troubleshooting, see Windows Help.
    <#> consecutive failure(s).
    Last success @ <date> <time>. 
    
    
  3. NTDS KCC, NTDS Replication, or ActiveDirectory_DomainService events with the 1256 status are logged in the directory service event log.

     

    Event IDEvent SourceEvent String

    1085

    noteNote
    Event 1085 is logged only if the NTDS Diagnostics value "5 Replication Events" has been set to a value of 1 or higher.

    NTDS Replication

    ActiveDirectory_DomainService

    Internal event: Active Directory Domain Services could not synchronize the following directory partition with the directory service at the following network address.

    1308

    NTDS KCC

    ActiveDirectory_DomainService

    The Knowledge Consistency Checker (KCC) has detected that successive attempts to replicate with the following domain controller has consistently failed.

    The Knowledge Consistency Checker (KCC) has detected that successive attempts to replicate with the following directory service has consistently failed.

When the destination DC fails to bind to the source DC using RPC, a win32 error code appears in the Repsfrom status for that partition - usually Schema or Configuration partitions because they are replicated at a higher priority. After an RPC bind failure has occurred, a cleanup routine will run to clear the destination DCs queue from that same source DC. This is done to avoid wasting time attempting to replicate with a DC that it cannot connect to. Because it has not attempted a sync for the partitions that have been cleared from the queue, a status 1256 is logged. In a scenario where destination DC replicates Schema, Configuration, and several GC non-writable partitions from the source DC, the win32 error status for the Schema and Configuration partitions that caused the RPC bind failure is logged. The destination DC will then cancel the pending replication tasks for the remaining partitions and log win32 error 1256 for the status.

In summary: 1256 is logged as the replication status per partition as a result of the destination DC cancelling the sync request from the source DC due to a connectivity failure previously encountered.

The win32 error 1256 should not be the focus of troubleshooting efforts, instead find the replication status that led to the RPC bind failure and then follow the corresponding article on TechNet. Microsoft Knowledge Base article 2498185 contains a list of Active Directory Replication troubleshooting articles.

In order to determine the actual win32 error to troubleshoot use one of the following methods:

  1. View repadmin /showreps or /showrepl output on the destination DC.

    1. Identify Source DC in the output and list all win32 status messages per partition.

    2. The win32 status that is listed that is not a 1256 should be the focus of troubleshooting efforts.

  2. Using repadmin /showrepl * /csv output:

    1. Filter column K, Last Failure Status:, clear 0 and (Blanks).

    2. Filter column C, Destination DSA: Clear (Select All) and select just the DC where the 1256 status is logged.

    3. If 1256 is logged on more than one Source DC, Filter column F, Source DSA:, clear (Select All) and Select just one DC to narrow the focus.

    4. Column K, Last Failure Status will list the 1256s along with the real win32 error that led to the RPC bind failure.

      In the following example, win32 error 1722 is logged for the Configuration and Schema partitions and should be the focus of troubleshooting.

       

      B

      C

      D

      E

      F

      H

      I

      J

      K

      Destination DSA Site

      Destination DSA

      Naming Context

      Source DSA Site

      Source DSA

      Number of Failures

      Last Failure Time

      Last Success Time

      Last Success Status

      London

      LONCONTOSODC

      CN=Configuration,DC=Contoso,DC=com

      London

      LONEMEADC

      11

      6/10/2010 17:35

      6/10/2010 14:50

      1722

      London

      LONCONTOSODC

      CN=Schema,CN=Configuration,DC=Contoso,DC=com

      London

      LONEMEADC

      11

      6/10/2010 17:35

      6/10/2010 14:50

      1722

      London

      LONCONTOSODC

      DC=ForestDnsZones,DC=Contoso,DC=com

      London

      LONEMEADC

      11

      6/10/2010 17:35

      6/10/2010 14:50

      1256

      London

      LONCONTOSODC

      DC=corp,DC=Contoso,DC=com

      London

      LONEMEADC

      11

      6/10/2010 17:35

      6/10/2010 14:50

      1256

      London

      LONCONTOSODC

      DC=EMEA,DC=Contoso,DC=com

      London

      LONEMEADC

      11

      6/10/2010 17:35

      6/10/2010 14:50

      1256

      London

      LONCONTOSODC

      DC=apac,DC=Contoso,DC=com

      London

      LONEMEADC

      11

      6/10/2010 17:35

      6/10/2010 14:50

      1256

  3. Initiate a manual replication sync between source and destination DCs using repadmin.

    Repadmin /replicate DestinationDC SourceDC DN of partition reporting status 1256
    
    (use /readonly switch for GC partition or /selsecrets switch if destination is an RODC)

    repadmin /replicate loncontosodc lonemeadc.emea.contoso.com dc=forestdnszones,dc=contoso,dc=com 
    DsReplicaSync() failed with status 1722 (0x6ba):
    The RPC server is unavailable.
    
    
    Take note that after manually initiating replication for the partition that the status has changed from 1256 to 1722:

     

    B

    C

    D

    E

    F

    H

    I

    J

    K

    Destination DSA Site

    Destination DSA

    Naming Context

    Source DSA Site

    Source DSA

    Number of Failures

    Last Failure Time

    Last Success Time

    Last Success Status

    London

    LONCONTOSODC

    CN=Configuration,DC=Contoso,DC=com

    London

    LONEMEADC

    11

    6/10/2010 17:35

    6/10/2010 14:50

    1722

    London

    LONCONTOSODC

    CN=Schema,CN=Configuration,DC=Contoso,DC=com

    London

    LONEMEADC

    11

    6/10/2010 17:35

    6/10/2010 14:50

    1722

    London

    LONCONTOSODC

    DC=ForestDnsZones,DC=Contoso,DC=com

    London

    LONEMEADC

    12

    6/10/2010 17:35

    6/10/2010 14:50

    1722

    London

    LONCONTOSODC

    DC=corp,DC=Contoso,DC=com

    London

    LONEMEADC

    11

    6/10/2010 17:35

    6/10/2010 14:50

    1256

    London

    LONCONTOSODC

    DC=EMEA,DC=Contoso,DC=com

    London

    LONEMEADC

    11

    6/10/2010 17:35

    6/10/2010 14:50

    1256

    London

    LONCONTOSODC

    DC=apac,DC=Contoso,DC=com

    London

    LONEMEADC

    11

    6/10/2010 17:35

    6/10/2010 14:50

    1256

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