PowerShell Script: Retrieving Distinguished name (DN) from A Fully Qualified Domain Name (FQDN)
By: Brenton Blawat
While there are many posts that describe the code to do this function, there aren’t many posts that provide variables with meaning or actually describe the syntax. This post describes the method by which you can retrieve a Distinguished Name from a Fully Qualified Domain Name.
Quick Reference:
Fully Qualified Domain Name (FQDN): division.domain.root
Distinguished Name (DC): DC=division,DC=Domain,DC=root
Canonical Name(CN): division.domain.root/OrganizationalUnit/
If you are looking for a quick way to obtain a Distinguished Name or Fully Qualified Domain Name See this article.
Mr. Weaver’s Code
Mark A. Weaver’s post Powershell – Recursive Group Membership, he describes the methods by which you can convert to and from multiple variables. Here is how Mr. Weaver performs the conversion operation:
1: function Convert-DNStoDN ($DNSName)
2: {
3: # Create an array of each item in the string separated by "."
4: $DNSArray = $DNSName.Split(".")
5: # Let's go through our new array and do something with each item
6: for ($x = 0; $x -lt $DNSArray.Length ; $x++)
7: {
8: #I don't want a comma after my last item, so check to see if I am on my last one and set
9: # $Separator equal to nothing.
10: # Remember that we need to go to Length-1 because arrays are "0 based indexes"
11: if ($x -eq ($DNSArray.Length - 1)){$Separator = ""}else{$Separator =","}
12: [string]$DN += "DC=" + $DNSArray[$x] + $Separator
13: }
14: return $DN
15: }
My Code – Explained
While my code is almost identical to Mr. Weaver’s Code, my only criticism is not providing useful variables and describing the functions. I can state, however, Mr. Weaver’s code provided a platform for a function that I use in a large production environment. I took the liberty to optimize the code (slightly) to meet my needs (Thank you sir!).
My Function looks like: Download PS1 Here
1: function Get-Domain {
2:
3: #Retrieve the Fully Qualified Domain Name if one is not supplied
4: # division.domain.root
5:
6: if ($FQDN -eq "") {
7: [String]$fqdn = [System.DirectoryServices.ActiveDirectory.Domain]::getcurrentdomain()
8: }
9:
10: # Create a New Array 'Item' for each item in between the '.' characters
11: # Arrayitem1 division
12: # Arrayitem2 domain
13: # Arrayitem3 root
14: $FQDNArray = $FQDN.split(".")
15:
16: # Add A Separator of ','
17: $Separator = ","
18:
19: # For Each Item in the Array
20: # for (CreateVar; Condition; RepeatAction)
21: # for ($x is now equal to 0; while $x is less than total array length; add 1 to X
22: for ($x = 0; $x -lt $FQDNArray.Length ; $x++)
23: {
24:
25: #If it's the last item in the array don't append a ','
26: if ($x -eq ($FQDNArray.Length - 1)) { $Separator = "" }
27:
28: # Append to $DN DC= plus the array item with a separator after
29: [string]$DN += "DC=" + $FQDNArray[$x] + $Separator
30:
31: # continue to next item in the array
32: }
33:
34: #return the Distinguished Name
35: return $DN
36: }
To use the Function to get the Distinguished Name of the Domain:
1: # Store the distinguished name in a variable named $objCrntDN.
2: $objCrntDN = Get-Domain
To use the function to get the Distinguished Name From a Fully Qualified Domain Name:
1: # Store the distinguished name in a variable named $objCrntDN
2: # Pass the Fully Qualified Domain Name with call
3: $objCrntDN = Get-Domain division.domain.root
Note: This function also works if you place the division.domain.root in parentheses with quotations:
Get-Domain(“division.domain.root”)
What’s Different??
While the output is basically the same, I’ve made a few changes in the code:
- “DNSname” is technically inaccurate, while I understand what he is meaning. He is referring to is the FQDN – a point of confusion for the readers.
- I made the passing of a FQDN (optional) – as sometimes we don’t need to determine the FQDN (outside the function) before we get the Distinguished Name.
- I named my function ‘Get-Domain’ . DNS-DN is a very specific function. Your will see that Marc has to call three different functions to convert between each of these. I chose to make a single function, and establish what the ultimate output will be. Name the function what you are getting or creating with the function. Get-Domain –> You already know what the output will be — the Domain.
- I removed the Else { $separator } out of the loop. In batch processing such as PowerShell, the interpreter will replace the $separator variable each time it passes through the loop for the items in the array. To make the code more efficient, I set the variable outside the loop as it only gets changed for the last array evaluation.
I would agree, I should revisit my variables for this function.
During the development process, I shifted mid-stream and didn’t go back to rename them.
I didn’t write “optimized” code since the number of iterations needed to go through an FQDN is relatively small. The added overhead of assigning the $Separator variable inside the for loop is minimal, at best. You are correct, though, that moving it outside of the loop is more efficient.
I also tend to explicitly define the input variables (parameters) to my functions.
In short, a very good post and I appreciate the feedback. I will probably take your suggestion regarding the inaccurate variable names.
Thanks!
— Mark
Mark A. Weaver
February 23, 2010
Mark,
I would like to state — your post provided me a stepping stone for a xml parsing solution (article to come) which I required in my production environment. I appreciate your blog as it has a wealth of information for PowerShell scripting. I often quickly write snippets of code and don’t really pay attention to the optimization of the code. That’s why we have communities, I guess.
Also to note, My final points in the “differences section” were more picky than anything. You are absolutely correct that the processing power required for the loop would be minimal.
One last item, the Fully Qualified Domain Name of the current domain can be returned quickly by using:
[String]$FQDN = [System.DirectoryServices.ActiveDirectory.Domain]::getCurrentDomain()
As with the Distinguished Name of the current domain with:
$root = [ADSI]”
$CurrentDN = $root.DistinguishedName
When I found these out — my beautiful FQDN to DN converter was useless and I wanted to cry.
Thanks for taking the time to review and comment!!
- Brent
brentblawat
February 23, 2010
This weblog is fantastic. There is generally all of the ideal information in the tips of my fingers. Many thanks and keep up the beneficial work!
Marketta Castellano
September 11, 2011