Not just another „wait for network“ script

Using Appsense Environment Manager to copy files at computer startup trigger can lead to headaches, because the action is executed by default without respect to the network connection / domain connection status. Therefore I created an intelligent Powershell script which can be used as a reusable condition prior to the copy jobs.

It does basically the following:

• Checks if a physical Ethernet adapter with an active layer-2 connection is present
• If so, the script tries to connect to the current domain controller by using the RootDSE
• If the DC is not reachable after a few tries, the script exits with return code 1, which equals “condition false”, otherwise it returns 1, which equals to “condition true”
• Sets an environment variable “_EMPNetworkStatus” with either status “LANConnect” or “disconnected”
• Writes the state to the application event log

 ################################################################################################################
# ScriptName: WaitForNetwork.ps1
# Author: Michael Rüefli / INSERTO AG
# Date: 30.05.2012
# Version: 1.01
# Description: Script checks if any physical ethernet adapter is connected and tries to reach current DC
#              The script writes to application eventlog
################################################################################################################
function writeevent() {
if ($args[0] -eq "-h") {
            Write-Host "usage: writeevent <event source> <event type:Information,Warning,Error <event id> > <event text>"
            break
}
#count the arguments
if ($args.count -lt 4)
{
            write-host "Error calling writeevent. Too few arguments. use option -h to see help" -foregroundcolor "red"
            break
}
trap 
{ # this installs an error handler for the function
            write-host "Error writing to eventlog:" $_.Exception.GetType().FullName + $_.Exception.Message
            continue; # exiting a trap with "continue" says to continue on the next line of the script
}

$source = $args[0]
$type = $args[1]
$eventid = $args[2]
$msg = $args[3]
#Create the source, if it does not already exist.
if(![System.Diagnostics.EventLog]::SourceExists($source))
{
            [System.Diagnostics.EventLog]::CreateEventSource($source,'Application')
             $logfile = 'Application'
}
else 
{
            $logfile = [System.Diagnostics.EventLog]::LogNameFromSourceName($source,'.')
             #write-host "Source exists and is registered in the $logfile Log"
}
 #Check if Event Type is correct
               switch ($type) 
               { 
                  "Information" {} 
                  "Warning" {} 
                  "Error" {} 
                  default {"Event type is invalid";exit}
               }
               $log = New-Object System.Diagnostics.EventLog 
               $log.set_log($logfile) 
               $log.set_source($source)
               $log.WriteEntry($msg,$type,$eventid)
}

#Check if the condition has already been run
If ($env:_EMPNetworkStatus -eq "LANConnect")
{
            write-output "Network connection is ready: Check has already been run"
            writeevent "WaitForNetworkScript" Information 2 "Network connection is ready: Check has already been run"
            exit 0
}

#Get All physical network adapter which are connected
$connected_physical_nics = Get-WmiObject Win32_NetworkAdapter | `
where {$_.AdapterType -eq "Ethernet 802.3" `
-and $_.PNPDeviceID -match 'PCI' `
-and $_.NetConnectionStatus -eq 2} 

#If an adapter is found, we assume client is in corporate network
If ($connected_physical_nics)
{
            #Get the current DC
    $currentDC = ([ADSI]“LDAP://RootDSE”).dnshostname
    #test connection to DC
    $i = 0
    While (!$connrst)
    {
        $connrst = Test-Connection -computername $currentDC -Count 1 -ea SilentlyContinue
        $i += 1
        If (!$connrst -and $i -ge 25)
        {
            #Timeout, we exit
            write-output "Timeout, we exit the script"
                                   writeevent "WaitForNetworkScript" Warning 1 "Timeout, network connection not ready: Error while trying to reach DC: $currentDC"
            exit 1
        }
        start-sleep -s 1
    }
    write-output "Network connection is ready: connected DC: $currentDC"
            writeevent "WaitForNetworkScript" Information 0 "Network connection is ready: connected DC: $currentDC"
            [ENVIRONMENT]::SetEnvironmentVariable("_EMPNetworkStatus", "LANConnect", "MACHINE")
    exit 0
}
Else
{
    write-warning "Network is disconnected"
    writeevent "WaitForNetworkScript" Warning 3 "Network is disconnected"
            [ENVIRONMENT]::SetEnvironmentVariable("_EMPNetworkStatus", "Disconnected", "MACHINE")
    exit 1
}