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Constructed Properties and LVR (Linked-Value Replication)

There was an interesting question that came up on the news group that discussed getting Active Directory replication metadata and while the question really wasn’t directly a Powershell question I found it intriguing. I knew I had the answer to the question back in my brain, but I couldn’t retrieve it.

Here is the Question:

“I’m working on a script where I need to compare the last time the member
attribute of a distribution group was modified (not the AD group object
itself) with the time stamp on a file (I’m exporting distribution group
memberships to a file, but only ones that have changed). The problem
I’m running into is that some Active Directory distribution groups
aren’t returning the member attribute when I look at the replication
meta data.

Any one have any thoughts on why some distribution groups return the
member attribute when I run GetReplicationMetadata and some don’t? This
returns all kinds of other attributes and their metadata, but naturally
not the one I’m interested in (it does some times, on some groups, but
not all). I could run my script by the actual AD object WhenChanged
attribute, but I’ll be processing a large number of lists and I want it
to run as fast as possible and since other attributes can change on a
group object, I don’t want to have to export a 8,000 member group if the
displayName changes, for example (I’m only interested in the member
attribute).
As always, any insight is appreciated.”

I thought about this for a bit and also consulted some AD friends and we determined the issue was LVR (Link Value Replication.) This was introduced in Windows 2003 (specifically 2003 Native Mode.)

Basically, LVR changed the unit of replication for some attributes to be the actual values. Prior to LVR if you changed group membership the entire attribute member would have to replicate. With LVR, just the link you added for user replicates.

As one can imagine this changed the Metadata and therefore GetReplicationMetadata() didnt get retrieve the data for you. Where does this leave us?

There were also a few constructed attributes that were added with 2003. One of which is called “msds-replvaluemetadata.” This attribute provided the metadata for these links in wonderful XML format. You will find code using this XML below.

Some Useful Links regarding LVR and Constructed Attributes:

Below is the script that resulted from the investigation


 

Get-GroupMemberMetadata.ps1

Param($GroupName)

$GroupMembers = @()

$root = [ADSI]""
$filter = "(&(objectclass=group)(name=$GroupName))"
$props = @("msDS-ReplValueMetaData")
$Searcher = new-Object System.DirectoryServices.DirectorySearcher($root,$filter,$props)
foreach($Group in $Searcher.findall())
{
    foreach($childMember in $Group.Properties."msds-replvaluemetadata")
    {
        $GroupMembers += [xml+site:msdn.microsoft.com”>XML]$ChildMember
    }
}

foreach($Member in $GroupMembers)
{
    $Member.ChildNodes
}

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