Determine if a NIC has Internet access (vs local, closed network)

Question

Is there some way in PowerShell to automatically determine which of multiple NICs has Internet access rather than an connection to a closed network?

Say, a computer has one NIC that can generally get out to the Web and another NIC that is connected to a small, scientific device network. They both have IP addresses and see a "network". Is there a generic way to determine which is Internet connected?

I know about:

gwmi win32_networkadapterconfiguration -filter "ipenabled = 'true'"

and

gwmi win32_networkadapter -filter "NetConnectionStatus LIKE '2'"

and

Get-NetAdapter | ? {($_.status -eq 'up')

but it's not clear to me that those filters are identifying Internet access vs just network access, and unfortunately, I don't have access to a machine with that kind of setup to test.

Thanks.

Answer 1

The Test-Connection cmdlet allows you to specify the source address with the -Source parameter. We can test the addresses being used by each adapter.

$adapters = Get-NetIPAddress -AddressFamily ipv4 | Where-Object InterfaceAlias -in (Get-NetAdapter | Select-Object -ExpandProperty Name) | Select-Object IPAddress,InterfaceAlias

$adapters | % {

    Test-Connection -Source $_.IPAddress -Destination 8.8.8.8 -ErrorAction SilentlyContinue | Out-Null

    if($?) {
        write-host $_.InterfaceAlias "(" $_.IPAddress ") can connect to the internet."
    }
    else {
        write-host $_.InterfaceAlias "(" $_.IPAddress ") failed to connect to the internet."
    }

}

Output:

Local Area Connection ( 10.1.1.2 ) can connect to the internet
Ethernet 2 ( 10.1.1.3 ) failed to connect to the internet.
Wireless Network Connection ( 10.1.1.4 ) failed to connect to the internet.

Answer 2

I believe that the best way would be to check which adapter the default route use.

Get-NetRoute -DestinationPrefix "0.0.0.0/0"

This would give you the ifIndex for the adapter that should be connected to the internet. The same ifIndex can be used to get the adapter...

Get-NetAdapter -InterfaceIndex <number from previous command>