Recipe 12.1 Determining if Two Domain Controllers Are in Sync

12.1.1 Problem

You want to determine if two domain controllers are in sync and have no objects to replicate to each other.

12.1.2 Solution

12.1.2.1 Using a command-line interface

By running the following two commands you can compare the up-to-dateness vector on the two DCs:

> repadmin /showutdvec <DC1Name> <NamingContextDN>
> repadmin /showutdvec <DC2Name> <NamingContextDN>

The Windows 2000 version of repadmin used a different syntax to accomplish the same thing. Here is the equivalent syntax:

> repadmin /showvector <NamingContextDN> <DC1Name>
> repadmin /showvector <NamingContextDN> <DC2Name>

12.1.2.2 Using VBScript

' This code prints the up-to-dateness vector for the DCs defined in
' the array arrDCList for the naming context defined by strNCDN
' ------ SCRIPT CONFIGURATION ------
' Set to the DN of the naming context you want to check the DCs against
strNCDN = "<NamingContextDN>"   ' e.g. dc=amer,dc=rallencorp,dc=com
' Enter 2 or more DCs to compare
arrDCList = Array("<DC1Name>","<DC2Name>")
' ------ END CONFIGURATION ---------

set objIadsTools = CreateObject("IADsTools.DCFunctions")

for each strDC in arrDCList
   WScript.Echo "Replication partner USNs for " & strDC & ":"
   intUSN = objIadsTools.GetHighestCommittedUSN(Cstr(strDC),0)
   if intUSN = -1 then
      Wscript.Echo "Error retrieving USN: " & objIadsTools.LastErrorText
      WScript.Quit
   end if
   WScript.Echo vbTab & strDC & " = " & intUSN

   intRes = objIadsTools.GetReplicationUSNState(Cstr(strDC), _ 
                                                Cstr(strNCDN),0,0)
   if intRes = -1 then
      Wscript.Echo "Error retrieving USNs: " & objIadsTools.LastErrorText
      WScript.Quit
   end if
   for count = 1 to intRes
      WScript.Echo vbTab & objIadsTools.ReplPartnerName(count) & _ 
                " = " & objIadsTools.ReplPartnerUSN(count) 
   next
   WScript.Echo
next

12.1.3 Discussion

To determine if two or more DCs are in sync from a replication standpoint, you need to compare their up-to-dateness vectors. Each domain controller stores what it thinks is the highest update sequence number (USN) for every DC that replicates a naming context. This is called the up-to-dateness vector. If you want to compare DC1 and DC2, you'd first want to get the up-to-dateness vector for DC1 and compare DC1's highest USN against what DC2 thinks DC1's highest USN is. If they are different, then you can deduce that DC2 has not replicated all the changes from DC1 yet. Next, compare the reverse to see if DC1 is in sync with DC2.