Identifying Active Network Interface

Identifying active network interface

The simplest way would be:

UdpClient u = new UdpClient(remoteAddress, 1);
IPAddress localAddr = ((IPEndPoint)u.Client.LocalEndPoint).Address;

Now, if you want the NetworkInterface object you do something like:

foreach (NetworkInterface nic in NetworkInterface.GetAllNetworkInterfaces())
{
   IPInterfaceProperties ipProps = nic.GetIPProperties();
   // check if localAddr is in ipProps.UnicastAddresses
}

Another option is to use P/Invoke and call GetBestInterface() to get the interface index, then again loop over all the network interfaces. As before, you'll have to dig through GetIPProperties() to get to the IPv4InterfaceProperties.Index property).

How to get current used network adapter

Following should help you.

NetworkInterface[] networks = NetworkInterface.GetAllNetworkInterfaces();

var activeAdapter = networks.First(x=> x.NetworkInterfaceType != NetworkInterfaceType.Loopback
                    && x.NetworkInterfaceType != NetworkInterfaceType.Tunnel
                    && x.OperationalStatus == OperationalStatus.Up 
                    && x.Name.StartsWith("vEthernet") == false);

The search is based on eliminating Network Adapters that are neither Loopback (Commonly used for testing) or Tunnel(commonly used for secure connection between private networks). Operational Status ensures that the Network interface is up and is is able to transmit data packets. The "vEthernet" is naming convention commonly used by Windows for Hyper-V Virtual Network Adapters

How to Determine Internet Network Interface in Java

On my laptop (running Windows 7, with Virtual Box and it's network interface installed) the following code prints out the name of my wireless interface along with my local address. It uses a brute force approach at the end of the day, but will only try and actually connect to addresses that are considered to be the best candidates.

// iterate over the network interfaces known to java
Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
OUTER : for (NetworkInterface interface_ : Collections.list(interfaces)) {
  // we shouldn't care about loopback addresses
  if (interface_.isLoopback())
    continue;

  // if you don't expect the interface to be up you can skip this
  // though it would question the usability of the rest of the code
  if (!interface_.isUp())
    continue;

  // iterate over the addresses associated with the interface
  Enumeration<InetAddress> addresses = interface_.getInetAddresses();
  for (InetAddress address : Collections.list(addresses)) {
    // look only for ipv4 addresses
    if (address instanceof Inet6Address)
      continue;

    // use a timeout big enough for your needs
    if (!address.isReachable(3000))
      continue;

    // java 7's try-with-resources statement, so that
    // we close the socket immediately after use
    try (SocketChannel socket = SocketChannel.open()) {
      // again, use a big enough timeout
      socket.socket().setSoTimeout(3000);

      // bind the socket to your local interface
      socket.bind(new InetSocketAddress(address, 8080));

      // try to connect to *somewhere*
      socket.connect(new InetSocketAddress("google.com", 80));
    } catch (IOException ex) {
      ex.printStackTrace();
      continue;
    }

    System.out.format("ni: %s, ia: %s\n", interface_, address);

    // stops at the first *working* solution
    break OUTER;
  }
}

_{(I've updated my answer with isReachable(...) based on Mocker Tim's answer.)}

One thing to watch out for. socket.bind(...) would bark at me that the address and port is already in use if I tried to run my code too fast in succession like the connection isn't cleaned up fast enough. 8080 should be a random port maybe.

Find through which network device user is connected to internet

Will this give you some hints?

Identifying active network interface

How do you find out which NIC is connected to the internet?

Technically, there is no "connected to the Internet". The real question is, which interface is routeable to a desired address. Right now, you're querying for the "default route" - the one that applies if no specific route to destination exists. But, you're ignoring any specific routes.

Fortunately, for 99.9% of home users, that'll do the trick. They're not likely to have much of a routing table, and GetBestInterface will automatically prefer wired over wireless - so you should be good. Throw in an override option for the .1% of cases you screw up, and call it a day.

But, for corporate use, you should be using GetBestInterface for a specific destination - otherwise, you'll have issues if someone is on the same LAN as your destination (which means you should take the "internal" interface, not the "external") or has a specific route to your destination (my internal network could peer with your destination's network, for instance).

Then again, I'm not sure what you plan to do with this adapter "connected to the Internet", so it might not be a big deal.

How do you determine which adapter is used?

In C#

foreach(var nic in NetworkInterface.GetAllNetworkInterfaces.Where(n => n.OperationalStatus == OperationStatus.UP)
{
    if(nic.GetIsNetworkAvailable())
    {
       //nic is attached to some form of network
    }
}

VB .NET

ForEach nic in NetworkInterface.GetAllNetworkInterfaces.Where(Function(n) n.OperationalStatus = OperationStatus.UP)
    If nic.GetIsNetworkAvailable() Then
       //nic is attached to some form of network
    End If
Next

This will only test active working Network Interfaces that are connected to an active network.

Powershell determine active ethernet adapter and his MAC

Something like ?

$adapters = Get-NetAdapter

foreach ($adapter in  $adapters){
    if($adapter.Status -eq "Up" -and $adapter.Name.Contains("Ethernet")){
    Write-Host $adapter.MacAddress 
    }
}

But still you can get more MAC addresses ..

Or using Get-NetRoute -DestinationPrefix '0.0.0.0/0' | Get-NetAdapter
Then

$activeMAC= Get-NetRoute -DestinationPrefix '0.0.0.0/0' | Get-NetAdapter
Write-Host $activeMAC.MacAddress

That should return only 1 MAC

How to determine which network adapter is connected to the internet

I ended up following a link to MSDN when I was reading this page where I found the GetBestInterface function. I was able to use that to find the adapter thats connected to the internet

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