Error 8418: The replication operation failed because of a schema mismatch between the servers involved

Matthieu Patou mat at
Fri Feb 12 07:58:21 UTC 2016

On 02/08/2016 10:20 AM, Sinelnikov Evgeniy wrote:
> Hello,
> During the past two weeks, I was able to reproduce on Samba-4.3.4 SCHEMA_MISMATCH problem, which looks like this:
> [root at dc02 ~]# samba-tool drs replicate dc01 dc02 dc=company3,dc=dd
> ERROR(<class 'samba.drs_utils.drsException'>): DsReplicaSync failed - drsException: DsReplicaSync failed (8418, 'WERR_DS_DRA_SCHEMA_MISMATCH')
>    File "/usr/local/samba/lib64/python2.7/site-packages/samba/netcmd/", line 348, in run
>      drs_utils.sendDsReplicaSync(self.drsuapi, self.drsuapi_handle, source_dsa_guid, NC, req_options)
>    File "/usr/local/samba/lib64/python2.7/site-packages/samba/", line 83, in sendDsReplicaSync
>      raise drsException("DsReplicaSync failed %s" % estr)
I assume that DC01 is Windows and DC02 is Linux, so you are asking 
Windows to replicate with Linux and it fails.
> [root at dc02 2016-02-08]# cat /etc/redhat-release
> CentOS Linux release 7.2.1511 (Core)
> [root at dc02 2016-02-08]# samba-tool ldapcmp ldap://dc01 ldap://dc02 --filter=whenChanged
> * Comparing [DOMAIN] context...
>      CN=Offline Address Book - /o\=Company3 Organisation/cn\=addrlists/cn\=,CN=Microsoft Exchange System Objects,DC=company3,DC=dd
>      CN=Offline Address Book - /o\3DCompany3 Organisation/cn\3Daddrlists/cn\3D,CN=Microsoft Exchange System Objects,DC=company3,DC=dd
> * Objects to be compared: 203
> * Result for [DOMAIN]: SUCCESS
> * Comparing [CONFIGURATION] context...
> * Objects to be compared: 4517
> * Comparing [SCHEMA] context...
> * Objects to be compared: 2343
> * Result for [SCHEMA]: SUCCESS
> * Comparing [DNSDOMAIN] context...
> * Objects to be compared: 33
> * Result for [DNSDOMAIN]: SUCCESS
> * Comparing [DNSFOREST] context...
> * Objects to be compared: 19
> * Result for [DNSFOREST]: SUCCESS
I think ldapcmp is lying, or there is another problem in the DRS code 
given the error that you have.

> Reproducable configuration includes Windows Domain Controller (Windows Server 2003, 64-bit)
> with Exchange 2003 (Windows Server 2003, 32-bit, not DC) extended AD schema and CentOS-7.2 with
> manually build Samba-4.3.4. This is simplified configuration of previously mailed configuration with same error:
> On Windows DC SCHEMA_MISMATCH problem looks like this (one of multiple types of events):
> Event Type:	Error
> Event Source:	NTDS Replication
> Event Category:	Replication
> Event ID:	1791
> Date:		27.01.2016
> Time:		14:35:09
> Computer:	DC01
> Description:
> Replication of Naming Context DC=company3,DC=dd from source a87941a1-9718-4f2a-91fe-bdb993dbd05b has been aborted. Replication requires consistent schema but last attempt to sync the schema had failed. It is crucial that schema replication functions properly. See previous errors for more diagnostics. If this issue persists, please contact Microsoft Product Support Services for assistance. Error 8418: The replication operation failed because of a schema mismatch between the servers involved..
> I traced this SCHEMA_MISMATCH error with gdb and found that dcesrv_drsuapi_DsGetNCChanges() function
> generates mismatched replicas for all name contexts except of cn=Schema,cn=Configuration,dc=company3,dc=dd.
> All other NC's are mismatched during replication process from Samba DC to Windows DC, but not vice versa.
More likely it's either dcesrv_drsuapi_is_reveal_secrets_request or 
It seems it's because we can't find in our schema the requested 
attribute from the attids
Can you:

1) Find out what is the real function that is causing this error code to 
be returned,
use something like ".DEBUG(0,(__location__ ": Entering function xyz"))
2)Print what is the the value of attid when the function returns 
> A this time I got decrypted DCERPC packets of DRSUAPI protocol using wireshark from metze's branch,
> and his patched version of MIT Kerberos:
> Also decrypted packets successfully parsed with ndrdump utility.
> I have next plans to debug this problem:
> 1. Try to find differences between mismatched and not mismatched of decrypted DRSUAPI packets:
>    * (Error of replication WindowsDC from SambaDC)
>    * (Success of replication SambaDC from WindowsDC)
> 2. Step by step send to Windows DC controlled list of replicas in fixed dcesrv_drsuapi_DsGetNCChanges()
> I'll be glad to know about other debugging techniques of this problem.
> All methods that I could try looks too complex.


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