How to test the connection to the default gateway without knowing the IP-Address of that Gateway?
Introduction
Imagine you are logged on a Windows Computer Server01. You want to check if Server02 has a connection to it’s gateway. Sure, you could run Test-Connection with the Source Parameter and do a remote ping. But you don’t know the IP-Address of server02’s gateway. There are 2 possibilities: a) Connect to Server02 and run ipconfig to find out Server02’s gateway address or b) Keep on reading my article 🙂
For checking the reachability of the localhost’s gateway, run the following One-Liner:
Test-Connection (Get-NetRoute -DestinationPrefix 0.0.0.0/0 | Select-Object -ExpandProperty Nexthop) -Quiet -Count 1
True, everything is fine.
Explanation: The IP-Address of the Default Gateway can be found in the routing table. The route 0.0.0.0/0 is called Default Route or Gateway of Last Resort. And that route with it´s next hop address is very important for the next step.
Testing the Gateway of Remote Hosts without knowing the IP-Address of the Gateway
One further thought: Why not use the -Source Parameter and combine it with our One-Liner? So I started playing … Is it possible to test the connection to server03’s gateway without knowing the IP-Address of server03’s gateway? Sounds crazy, but: Yes, it is.
I am logged on server dc01 (dc01 and server03 share the same domain) and do the following:
$Name=Read-Host "Computername?" $Test=Invoke-Command -ComputerName $Name {Get-NetRoute -DestinationPrefix 0.0.0.0/0 | Select-Object -ExpandProperty Nexthop} Test-Connection -Source $Name -Destination $Test -Count 1
Nice. The IP-Address of server03’s gateway is 192.168.0.1. And yes, server 03 can reach it’s gateway. I don’t care about the IP-Address. 😉 The default route always gives me the IP-Address of the Default Gateway, regardless of the number of network cards and configured IP-Addresses.
For more about Test-Connection see my article The modern version of ping: Test-Connection.
Have fun playing with Test-Connection and Default Routes!
Categories: PowerShell
My name is Patrick Gruenauer. From Austria.
SID-500.COM 
Nice idea, but I don’t understand, why you need to include the source parameter for invoking the cmdlets on Server03. You’re already executing it on Server03, aren’t you?
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Thank you for your kind words. I was logged on server dc01. See “I am logged on server dc01 (dc01 and server03 share the same domain) and do the following: ……..” Regards, P
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OK, now I understand.
I thought you would execute “Test-Connection” via Invoke-Command as well. You would even save a few keystrokes:
$Name=Read-Host “Computername?”
Invoke-Command -ComputerName $Name {$Test=Get-NetRoute -DestinationPrefix 0.0.0.0/0 | Select-Object -ExpandProperty Nexthop; Test-Connection -Destination $Test -Count 1}
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Sometimes I decide to make it more user-friendly and readable. Thank’s for your input!
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