<#
Find-ADsiteFromIP.ps1
Alan Kaplan 11/30/2018
#>

#Clear variables
$errmsg = $site = $subnet = $dcList = ''

Write-Host "This script will get the AD site and DC(s) for an IP address"
$TestIP = Read-Host -Prompt "Enter an IP v4 address"

#Get site using NLTest, convert to object
$NLTretval = nltest /dsaddresstosite:$TestIP 2> $null
if ($NLTretval[2].length -eq 1) {  
    $errmsg = "Could not find site for $testIP"
}
else {
    $a = [regex]::Split($NLTretval[2].Trim(), '  ')
    $site = $a[1]
    $Subnet = $a[2]    
} 

if ($Subnet -match 'null') {  
    $errmsg = "Could not find defined subnet for $testIP"
}

if ($errmsg -eq '') {
    #Get ConfigurationNamingContext
    $objRootDSE = [System.DirectoryServices.DirectoryEntry] "LDAP://rootDSE"
    $ConfigurationNC = $objRootDSE.configurationNamingContext

    #Search Sites
    $Searcher = New-Object System.DirectoryServices.DirectorySearcher 
    $Searcher.SearchScope = "subtree" 
    $Searcher.SearchRoot = "LDAP://CN=Sites`,$ConfigurationNC"

    #Get list of all servers
    $searcher.Filter = "(objectclass=Server)"
    $siteInfo = ($Searcher.FindAll())

    #filter for AD path results
    $filter = '*CN=' + $Site + '*'

    #Concatenate server names
    $dcList = (
        (($siteInfo | Where-Object {$_.path -like $filter}).properties.name)| 
            Sort-Object
    ) -join ', '
}

#PS Custom Object
$NLTinfo = [PSCustomObject]@{
    IP        = $TestIP
    Subnet    = $Subnet
    Site      = $site
    'DC List' = $dcList
    Errors    = $errmsg
}

$NLTInfo
Pause