Use powershell to find Which Adapter is being used - windows

Question

I have three Ethernet Adapters on my windows machine. All show status connected and up.
I want to understand how can I find from PowerShell which adapter is being used to connect to the internet. Via UI I can see Ethernet0 being the one but how to find that via powershell. Any ideas are welcomed. Especially something that is supported in powershell 2 as well.
PS C:\Users> Get-NetAdapter -physical
Name InterfaceDescription ifIndex Status
Ethernet0 Intel(R) 82574L Gigabit Network Conn... 15 Up
Ethernet1 Intel(R) 82574L Gigabit Network Co...#2 9 Up
Ethernet2 Intel(R) 82574L Gigabit Network Co...#3 4 Up

Answer 1

Get-NetAdapterStatistics will return information such as traffic on the adapter specified which you can use to create a script to listen for a change in value.
Here's some quick and dirty scripting using that cmdlet:
$keySet = #{}
:loop while ($true) {
$adapters = Get-NetAdapter -Physical | Get-NetAdapterStatistics
foreach ($adapter in $adapters)
{
if (-not $keySet.ContainsKey($adapter.Name)) {
$null = $keySet.Add($adapter.Name,$adapter.ReceivedBytes)
}
if ($adapter.ReceivedBytes -ne $keySet[$adapter.Name]) {
Write-Output -InputObject $adapter.Name
Break loop
}
}
}
By creating a hashtable, you can append the Name and ReceivedBytes property to it. Then reference the key values later on in your second iteration to compare from your first iteration. Using a while loop, you can set a constant listener to see which adapter will be the first to receive a packet; this in turn gives a different value of what's stored in $keySet and will break you out of the loop but not before outputting the Name of the adapter.
The issue comes with the adapters that are receiving any other traffic. That's something to be weary of. That is also something you can improve on later on down the road if you want to continue to use this example.
Hopefully this gets you on the right track.