Replication Warnings? – It could be just one Attribute.

Active Directory can be a funny beast.  This week, I noticed a reoccuring replication error that didn’t seem to be sorting itself within a reasonable time frame.  I was seeing NTDS Replication Warning 1083, referencing a specific user account: 

Event Type: Warning
Event Source: NTDS Replication
Event Category: Replication
Event ID: 1083
Date:  10/3/2011
Time:  11:45:00 AM
User:  NT AUTHORITY\ANONYMOUS LOGON
Computer: DC1
Description:
Active Directory could not update the following object with changes received from the domain controller at the following network address because Active Directory was busy processing information.

Object:
CN=Joe Smith,OU=Accounts,DC=mydomain,DC=org
Network address:
a5b5b72d-c74b-486a-9dfa-f6516f37b38b._msdcs.caclo.org

Following it was the informational event 1955 about a write conflict:

Event Type: Information
Event Source: NTDS Replication
Event Category: Replication
Event ID: 1955
Date:  10/3/2011
Time:  11:45:00 AM
User:  NT AUTHORITY\ANONYMOUS LOGON
Computer: DC1
Description:
Active Directory encountered a write conflict when applying replicated changes to the following object.

Object:
CN=Joe Smith,OU=Accounts,DC=mydomain,DC=org
Time in seconds: 0 

After some research I tried the following troubleshooting steps:

1) Moved the offending user to a different OU temporarily to see if the problem resolved.  This essentially “tickles” AD into replicating that particular user. I recieved the same messages, but the user’s CN had been updated to the new OU.
2) Used the LDP tool to see if there was duplicate entries for this user somehow, but only one instance was found.
3) Used repadmin to look at the time stamps of various attributes on the account, particular one with a time stamp close to the time that the replication warnings started appearing in the event log.

Repadmin was where I had the most luck.  You’ll want to run the following command for Windows 2003 SP2 DCs:

repadmin /showobjmeta DC1 “CN=Joe Smith,OU=Accounts,DC=mydomain,DC=org”

This will return a list of attributes with timestamps.  In my case it was the attribute related to the last password change, which was the only one that had a timestamp of the same date when the errors began.  I reset the password on the account to “tickle” that particular attribute and the replication completed without any complaint.

Some anticodotal stories on the Internet indicate that this attribute can cause trouble if replication occurs while an account happens to be locked out.  In this case, the account was for a consultant who didn’t log in very often, so the locked account went unnoticed for some time, causing the replication issue.

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