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Tuesday, June 7, 2016

Don’t use PING!

One of the questions that I often get is “How do I know if a client is online?” Traditionally we would PING the client.  PowerShell has a cmdlet called Test-Connection.  It essentially is the PING command, but gives you an object as the output. Let’s see the difference.

PS C:\> Ping 8.8.8.8

Pinging 8.8.8.8 with 32 bytes of data:
Reply from 8.8.8.8: bytes=32 time=19ms TTL=56
Reply from 8.8.8.8: bytes=32 time=20ms TTL=56
Reply from 8.8.8.8: bytes=32 time=20ms TTL=56
Reply from 8.8.8.8: bytes=32 time=20ms TTL=56

Ping statistics for 8.8.8.8:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 19ms, Maximum = 20ms, Average = 19ms

This is what most IT Pros are seeing.  Let’s try to use this information.
As always, we need to see what properties are available to us to use.
PS C:\> Ping 8.8.8.8 | GM


   TypeName: System.String

Name             MemberType            Definition                                                                                                                
----             ----------            ----------                                                                                                                 
Clone            Method                System.Object Clone(), System.Object ICloneable.Clone()                                                                   
CompareTo        Method                int CompareTo(System.Object value), int CompareTo(string strB), int IComparable.CompareTo(System.Object obj), int ICompa...


OK, let’s just stop right here.  The TypeName is System.String.  In other words, the information returned from PING is nothing but useless characters. Let’s try Test-Connection.
PS C:\> Test-Connection -ComputerName 8.8.8.8

Source   Destination IPV4Address  IPV6Address Bytes Time(ms)
------   ----------- -----------  ----------- ----- --------
JASONPC2 8.8.8.8     8.8.8.8             32       19      
JASONPC2 8.8.8.8     8.8.8.8                   32       21      
JASONPC2 8.8.8.8     8.8.8.8                   32       23      
JASONPC2 8.8.8.8     8.8.8.8                   32       20      

Now let’s check the TypeName

   TypeName: System.Management.ManagementObject#root\cimv2\Win32_PingStatus

Name                           MemberType     Definition                                                                                                          
----                           ----------     ----------                                                                                                         
PSComputerName                 AliasProperty  PSComputerName = __SERVER                                                                                          
Address                        Property       string Address {get;set;}                                                                                           
BufferSize                     Property       uint32 BufferSize {get;set;}       

Now we are talking.  This give us an object that we can use.  There is just one problem, we are relying on ICMP Echo Requests.  If you have PowerShell remoting turned on, you can actually use it to verify if a client is online.  Take a look at the code.

Function Test-Online
{
[CmdletBinding()]
Param (
    [parameter(Mandatory=$true,
    ValueFromPipeline=$true)]
    [String[]]
    $Nodes
)
PROCESS {
    ForEach ($N in $Nodes)
    {
        $Obj = New-Object -TypeName PSObject -Property @{
            ComputerName = $N
            Online = $False
            DateTime = (Get-Date)
        }
        Try {
            $SO = New-PSSessionOption -OpenTimeout 500
            $S = New-PSSession -ComputerName $N -ErrorAction Stop -SessionOption $SO
            $Obj.Online = $True
            $S | Remove-PSSession
        }
        Catch {

        }
        Write-Output $Obj
    } # END: ForEach ($N in $Nodes)
} # END: PROCESS
<#
.SYNOPSIS
Uses PowerShell Remoting to test if a node is online.

.DESCRIPTION
Uses PowerShell Remoting to test if a node is online.

.PARAMETER Nodes
The name of the nodes to be tested.

.Example
"SVR1", "SVR2" | Test-Online

ComputerName  DateTime               Online
------------  --------               ------
SVR1          6/7/2016 10:30:59 AM     True
SVR2          6/7/2016 10:31:00 AM    False

Test to determine if a list ofnodes are online.

.Example
Get-ADComputer -Filter * | Select-Object -ExpandProperty Name | Test-Online

ComputerName  DateTime               Online
------------  --------               ------
SVR1          6/7/2016 10:30:59 AM     True
SVR2          6/7/2016 10:31:00 AM    False

Test all clients in Active Directory to see if they are online.

.NOTES
Any node that does not have PowerShell Remoting enabled will report an online status of False.

.NOTES
===============================================================================
== Cmdlet: Test-Online                                                       ==
== Author: Jason A. Yoder                                                    ==
== Company: MCTExpert of Arizona                                             ==
== Date: June 7, 2016                                                        ==
== Copyright: All rights reserved.                                           ==
== Version: 1.0.0.0                                                          ==
== Legal: The user assumes all responsibility and liability for the usage of ==
== this PowerShell code.  MCTExpert of Arizona, Its officers, shareholders,  ==
== owners, and their relatives are not liable for any damages.  As with all  ==
== code, review it and understand it prior to usage.  It is recommended that ==
== this code be fully tested and validated in a test environment prior to    ==
== usage in a production environment.                                        ==
==                                                                           ==
== Does this code make changes: NO                                           ==
===============================================================================
#>
} # END: Function Test-Online

Here is what it looks like when used:
"SVR1", "SVR2" | Test-Online

ComputerName  DateTime               Online
------------  --------               ------
SVR1          6/7/2016 10:30:59 AM     True
SVR2          6/7/2016 10:31:00 AM    False

For every node that we pass to this cmdlet, a custom object is created.  We provide the value on the ComputerName and the DateTime that we are testing.  We also set the value for Online to be $False.  Next, we attempt to create a PowerShell Session to this remote client.  If the connection is made, we set the value of Online to $True and close the session.  We then place the object in the pipeline.  If the session does not get established, then the object is placed in the pipeline with the Online value still set to $False.


PowerShell remoting is already enabled on all Windows Server 2012 and newer.  Why not enable it on your clients?  This allows your remote connections to use WS-MAN as the remoting protocol as opposed to the older DCOM.  

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