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I have two domain controllers, one where the USN in question is always the same values (current and original), while the other one the original USN is roughly 6 numbers lower than the current value.

What does this mean? How could this potentially affect my applications?

Here is a screenshot of the original and current USN's differentiating: enter image description here

Chris Dale
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1 Answers1

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Each Domain Controller holds a local USN counter that gets incremented by each write to the DC's database replica.

A digression between Current and Original simply means that the object was changed since creation.

You can inspect the USN at the last write time for each attribute on an object with repadmin.exe:

repadmin /showobjmeta DC01 "CN=SomeObject,OU=Computers,DC=domain,DC=tld"

Try this for size:

  1. Create a new user account object named "TestUser" in the users OU
  2. Inspect the output of /showobjmeta from each domain controller (USNs should vary by DC):
    repadmin /showobjmeta * "CN=TestUser,OU=Users,DC=domain,DC=tld"
  3. Make a change to an object attribute, "Description" is a great candidate
  4. Run repadmin /showobjmeta again - the description attribute will have a newer USN on all Domain Controllers that have received the update, as well as on the Domain Controller on which you performed the update. Non-updated attributes (see whenCreated and objectGUID for control) will still have the original USN

Hope this makes sense

Mathias R. Jessen
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  • Thank you, it does make sense. In my specific example, dose that mean that the object have been updated 6 times through replication? Considering the difference between original and current is 6, I guess that there has been a update on the object 6 times from another DC. – Chris Dale Oct 21 '13 at 09:46
  • Not necessarily. The USN is incremented with each write, so the object could have been created, 5 changes made to other objects and then one update to the object in question – Mathias R. Jessen Oct 21 '13 at 10:07