Testing LDAP and LDAPS connectivity with PowerShell

function Test-LDAPPorts {
    [CmdletBinding()]
    param(
        [string] $ServerName,
        [int] $Port
    )
    if ($ServerName -and $Port -ne 0) {
        try {
            $LDAP = "LDAP://" + $ServerName + ':' + $Port
            $Connection = [ADSI]($LDAP)
            $Connection.Close()
            return $true
        } catch {
            if ($_.Exception.ToString() -match "The server is not operational") {
                Write-Warning "Can't open $ServerName`:$Port."
            } elseif ($_.Exception.ToString() -match "The user name or password is incorrect") {
                Write-Warning "Current user ($Env:USERNAME) doesn't seem to have access to to LDAP on port $Server`:$Port"
            } else {
                Write-Warning -Message $_
            }
        }
        return $False
    }
}
Function Test-LDAP {
    [CmdletBinding()]
    param (
        [alias('Server', 'IpAddress')][Parameter(Mandatory = $True)][string[]]$ComputerName,
        [int] $GCPortLDAP = 3268,
        [int] $GCPortLDAPSSL = 3269,
        [int] $PortLDAP = 389,
        [int] $PortLDAPS = 636
    )
    # Checks for ServerName - Makes sure to convert IPAddress to DNS
    foreach ($Computer in $ComputerName) {
        [Array] $ADServerFQDN = (Resolve-DnsName -Name $Computer -ErrorAction SilentlyContinue)
        if ($ADServerFQDN) {
            if ($ADServerFQDN.NameHost) {
                $ServerName = $ADServerFQDN[0].NameHost
            } else {
                [Array] $ADServerFQDN = (Resolve-DnsName -Name $Computer -ErrorAction SilentlyContinue)
                $FilterName = $ADServerFQDN | Where-Object { $_.QueryType -eq 'A' }
                $ServerName = $FilterName[0].Name
            }
        } else {
            $ServerName = ''
        }

        $GlobalCatalogSSL = Test-LDAPPorts -ServerName $ServerName -Port $GCPortLDAPSSL
        $GlobalCatalogNonSSL = Test-LDAPPorts -ServerName $ServerName -Port $GCPortLDAP
        $ConnectionLDAPS = Test-LDAPPorts -ServerName $ServerName -Port $PortLDAPS
        $ConnectionLDAP = Test-LDAPPorts -ServerName $ServerName -Port $PortLDAP

        $PortsThatWork = @(
            if ($GlobalCatalogNonSSL) { $GCPortLDAP }
            if ($GlobalCatalogSSL) { $GCPortLDAPSSL }
            if ($ConnectionLDAP) { $PortLDAP }
            if ($ConnectionLDAPS) { $PortLDAPS }
        ) | Sort-Object
        [pscustomobject]@{
            Computer           = $Computer
            ComputerFQDN       = $ServerName
            GlobalCatalogLDAP  = $GlobalCatalogNonSSL
            GlobalCatalogLDAPS = $GlobalCatalogSSL
            LDAP               = $ConnectionLDAP
            LDAPS              = $ConnectionLDAPS
            AvailablePorts     = $PortsThatWork -join ','
        }
    }
}

Test-LDAP -ComputerName 'AD1','AD2' | Format-Table