Create a Hash Table with AD Domain DNS Root and NetBIOS Names

I frequently get requests to modify or lookup a list of user names in a CSV file where the username is NTDomain\SamAccountName.   Get-ADUser will let you use the NT domain as a server name, but in my experience it is slower than using the domain’s FQDN.  Before I import the list in my code, I run Get-DomainNameHashTable, which returns the hash object $domHash.  The name in $domHash is the NT/NetBIOS domain name (CONTOSO), and the value is the DNS Root/FQDN for the domain (CONTOSO.COM).

Function Get-DomainNameHashTable {
    $Forest = ([System.DirectoryServices.ActiveDirectory.Forest]::GetCurrentForest())
    $DomainList = ($Forest.Domains).Name

    #Bill Stewart
    function Invoke-Method([__ComObject] $object, [String] $method, $parameters) {
        $object.GetType().InvokeMember($method, "InvokeMethod", $NULL, $object, $parameters)
    }

    $NameTranslate = New-Object -ComObject "NameTranslate"
    #INITTYPE_GC
    Invoke-Method $NameTranslate "Init" ((3), "")
    $Script:domHash = @{}
    $domainList | 
        ForEach-Object { 
        $dn = "DC=" + $($_).replace(".", ",DC=")
        #Set is From Type 1779 Get is to Type NT4
        Invoke-Method $NameTranslate "Set" ((1), $dn)
        $NTDom = [string](Invoke-Method $NameTranslate "Get" (3)).Replace("\", "")
        $domHash.Add($NTDom.ToUpper(), $_.ToUpper())
    }
    [System.Runtime.Interopservices.Marshal]::ReleaseComObject($NameTranslate) | Out-Null
    $domHash
}

After reading the CSV file, I split the user name name on “\”, then lookup up the DNS root for Contoso with $domHash[‘Constoso’], or $domHash.item(‘Constoso’). Here is an example:

$userlist = import-csv "$env:userprofile\Desktop\userlist.csv"
Get-DomainNameHashTable
ForEach-Object ($FullName in $$userList.Name){
  $t = $FullName.split("\")
  $NTDom = $t[0]
  $SamName = $t[1]
  $Domain = $domHash[$NTDom]
  Get-ADUser -Server $domain -SamName
}