This quick free lesson in PowerShell teaches you how to use the ping class to get a list of offline computers. It is fast and easy, and the results are much easier to work with than using ping.exe.
Hey. This post is from 2010. When it was written there was no “Test-NetConnection” cmdlet. Things are even easier now.
Just use Test-NetConnection instead of the .Net Ping Class.
Using the .Net Ping Class
PowerShell is built for speed, and it leverages the .Net framework to make this happen.
To check the computers status, a Ping request is sent to each computer in a list.
To start pinging, an object of the Ping class is instantiated:
$ping = new-object system.net.networkinformation.ping
Easy, right?
This avoids having to use the sloppy mess of processing through the text returned by ping.exe.
What is the difference?
By using a .Net object for the ping results, we can still use the object that is returned. We can save the objects themselves and reference them back later. The beauty of PowerShell. The Power. We want (and get) much more information. The results of
ping 192.168.1.1
is a wall of text (an array of 11 strings, actually,) while the result of
$ping.send(“192.168.1.1”)
Is a .Net object of the “system.net.networkinformation.pingreply” class. A pingreply has a property (named ‘status’) that tells us if the ping was successful or not; the address of the ping; and the miliseconds that it takes to get the reply.
To get results that are usable, keep your ping replies in a variable of results, like this:
$pingreturns = $ping.send(“192.168.1.1”)
Alright, we’ve got the base now for finding out if the computer is reachable.
Get Your Computer List Ready
The list of computers we want to ping. You don’t have to limit your list to only computers. If the network device has Internet Control Message Protocol (ICMP) available (most do) and turned on (depends), it will return pings when they are received. You could ping network printers, or routers, for example.
Here are some examples of loading the ping list:
Get Computer List From Textfile
If you have several computers that you want to check frequently, add them to a text file so it’s easy to save, and easy to update the file instead of modifying the script.
“computer1”,”computer2”,”192.168.1.100”,”192.168.1.1” | out-file c:\users\public\documents\pinglist.txt
Now you’ve got a text file. Quake with fear, bitches! Note the use of hostnames and IP Addresses. It’s fine to do that, you can mix and match. That list is 4 computers, not a collection of 2 computers listed by hostname and IP.
Update the list of computers as needed.
To load the list of computers:
$complist = gc c:\users\public\documents\pinglist.txt
Get Computer List Manually
$complist = “computer1”, “computer2”
Easy, simple, and easy. To change the list, you’d change it in the script itself.
Get Computer List From Other Parts Of The Script
$servers = get-qadcomputer –service domain.com *serv*
$complist = $servers | select name
This seems normal, but it’s actually different, because you’re saving a list of objects into $complist, instead of a list of strings. Here’s the difference
PS C:\ScriptGenius> $stringlist = "Computer1", "Computer2"
PS C:\ScriptGenius> $stringlist[0]
Computer1
PS C:\ScriptGenius> $stringlist[0].gettype()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True String System.Object
Compare that to the item in the object list
PS C:\ScriptGenius> $objectlist = get-qadcomputer *work* | select name
PS C:\ScriptGenius> $objectlist[0]
Name
----
SOFTGRIDWORK2
PS C:\ScriptGenius> $objectlist[0].gettype()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True False PSCustomObject System.Object
While the two seem at first to be the same:
$ping.send($stringlist[0])
Works.
$ping.send($objectlist[0])
Does not, but it is at least salvageable. To make that ping work, the name property of the psCustomObject (the computer account returned by get-qadcomputer) must be referenced.
$ping.send($objectlist[0].name)
Works.
Get Computer List From an IP Range
This will do an IP sweep for a subnet, pinging along the way.
1..254 | % {$ping.send(“192.168.1.$_”) | select address, status}
Putting it All Together
Now that we’ve seen the pieces, here’s how it all works together.
$computers = get-content C:\scriptgenius\computers.txt
$ping = new-object system.net.networkinformation.ping
$pingreturns = @()
foreach ($entry in $computers) {
$pingreturns += $ping.send($entry)
}
An array is used here to collect multiple ping results. When completed, this can be used like this.
$pingreturns[4].status
or
$pingreturns | ? {$_.status –ne “success”} | select address
Instead of piping that to “select address” we could just as easily take action on those failed IP addresses. Like sending the list of offline computers to the administrative team or on-call person via email.
