Find through which network device user is connected to internet

Question

Using the code below I will get all network interfaces which are enabled and functional on the machine.

Private netIntrfc As NetworkInterface() = NetworkInterface.GetAllNetworkInterfaces()
For i As Integer = 0 To netIntrfc.Length - 1
  If netIntrfc(i).OperationalStatus = OperationalStatus.Up Then
    netDevicesList.Items.Add(netIntrfc(i).Name.ToString)
  End If
Next

But my problem is how to get the default one, the one( ethernet adapter ) through which user is connected to internet?

I need to change some settings of default( through which user is connected to internet ) adapter. settings I change through registry so I could sample add same settings for each network interface but that could cause problems and makes no point then.

EDITED:

For now I have done like code below, so if this can help someone other, but if someone has a better solution or more reliable then send please.

Dim u As UdpClient = New UdpClient(System.Net.Dns.GetHostName, 1)
Dim localAddr As IPAddress = CType(u.Client.LocalEndPoint, IPEndPoint).Address

Private netIntrfc As NetworkInterface() = NetworkInterface.GetAllNetworkInterfaces()
For i As Integer = 0 To netIntrfc.Length - 1
  If netIntrfc(i).OperationalStatus = OperationalStatus.Up Then
    For Each uni As NetworkInformation.UnicastIPAddressInformation In ipProps.UnicastAddresses
      If uni.Address.ToString = localAddr.ToString Then
        netDevicesList.Items.Add("DEFAULT: " & netIntrfc(i).Name.ToString)
        DEFDEVID = netIntrfc(i).Id.ToString
      End If
    Next
    netDevicesList.Items.Add(netIntrfc(i).Name.ToString)
  End If
Next

Thanks Thomas-Li and this post

Answer 1

Will this give you some hints?

Identifying active network interface

Answer 2

i ported your code to c#, i hope you don' t mind

    static void Main(string[] args)
    {
        UdpClient u = new UdpClient(System.Net.Dns.GetHostName(), 1);
        IPAddress localAddr = (u.Client.LocalEndPoint as IPEndPoint).Address;
        NetworkInterface[] netIntrfc  = NetworkInterface.GetAllNetworkInterfaces();
        for (int i = 0; i < netIntrfc.Length - 1; i++)
        {
            if (netIntrfc[i].OperationalStatus == OperationalStatus.Up) 
            {
                IPInterfaceProperties ipProps = netIntrfc[i].GetIPProperties();
                foreach (UnicastIPAddressInformation uni in ipProps.UnicastAddresses) 
                {
                    if (uni.Address.ToString() == localAddr.ToString()) 
                    {
                        Console.WriteLine("DEFAULT: " + netIntrfc[i].Name.ToString());
                        Console.WriteLine(netIntrfc[i].Id.ToString());
                    }
                }
            } 
        }
    }