Powershell Pull AD Group and Subgroup Endless Loop - powershell

Question

My script is hitting the active directory to pull AD groups and their subgroups.
I will be adding in Get-ADGroupMember Where-Object { $_.ObjectClass -eq "user" }) to the script but right now the script runs endlessly.
I checked the CSV file and data is being pushed into it, I just do not know why this is running endlessly.
I am still new to Powershell and may have overlooked something.
Do I need to add some sort of catch or exit? I read that exit closes the loop before it can execute completely.
My Script:
Clear-Host
#Import-Module ActiveDirectory
Write-Host -ForegroundColor Green "Starting"
$logfile = "C:\temp\logfile.csv"
"Domains,Groups,Nested" | Add-Content $logfile
$grp_list = Import-Csv "C:\temp\Copy_lp.csv"
$domains = #()
$dom = Import-Csv "C:\temp\Copy_lp.csv" |
Select-Object -Unique -ExpandProperty "Domain Group"
foreach ($domain in $dom) {
$domains += $domain.Split('\')[0]
}
$domains = $domains | Select-Object -Unique
foreach ($domain in $domains) {
Write-Host "Domain:" $domain
Get-ADGroup -Filter * -Server $domain |
ForEach-Object {
$group = $_.Name
$grps = (Get-ADGroupMember $group -Server $domain |
Where-Object { $_.ObjectClass -eq "Group" })
$grps | ForEach {
Write-Host "Group: " $_.Name
"$domain,$($_.Name),$group" | Add-Content $logfile
}
}
}
Write-Host -ForegroundColor Green "Done"
Update
This was answered by Tomer. I had taken the output CSV from a previous script that was executed to look at user permissions at the database level. So when a user was mapped to multiple databases (user also belonged to different groups and subgroups) within the instance and would appear numerous times. So as my script went through the list it would re-run the same AD Group(s) over and over. I still do not understand why it would continuously run but once I altered the CSV file to have just a domain list it executed and spit out the output I was looking for. I did not put this as the answer because I felt Tomer deserved the credit. Thank you all for your help.

Answer 1

In Active Directory, membership self-loops are permitted. So for example, group A may contain another group B which may contain group A again. Therefore, simple enumeration of the member-of relation can lead to an infinite loop.
An easy way to solve it is to store the DNs you've already seen, and not going over them again.