Why is GetIsNetworkAvailable() always returning tr

Question

I have this method:

public static void testConnection()
    {
        if (System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable())
        {
            System.Windows.MessageBox.Show("This computer is connected to the internet");
        }
        else
        {
            System.Windows.MessageBox.Show("This computer is not connected to the internet");
        }
    }

I suppose it would tell me whether the connection is available or not but it always return true (and print the 1st message) even when I'm sure there is no connection. What I'm doing wrong?

P.S.: I'm still learning C#.

Answer 1

I suppose it would tell me whether the connection is available or not but it always return true (and print the 1st message) even when I'm sure there is no connection.

You have a different opinion on the meaning of 'connection' than the manual does. As far as the operating system is concerned, you have a connection when there is a patched ethernet cable connected to your NIC, or when your wireless card is connected to an wireless access point, or any connection is active.

The manual also explains this:

NetworkInterface.GetIsNetworkAvailable:

Indicates whether any network connection is available.

If you want to detect internet connectivity, take a look at the InternetGetConnectedState() (or InternetCheckConnection(), to check for accessibility of a specific host) methods from the WinINet API.

Answer 2

I think this method is more appropriate:

   public static bool getIsInternetAccessAvailable()
    {
        switch(NetworkInformation.GetInternetConnectionProfile().GetNetworkConnectivityLevel())
        {
            case NetworkConnectivityLevel.InternetAccess:
                return true;
            default:
                return false;
        }
    }

Answer 3

Please correct me if I am wrong but as far as I can see the method you are using is checking network connectivity and not necessarily internet connectivity. I would assume if you are on a network of any sort this would return true regardless of the internet being available or not? See this.

I have noticed that one way of checking for internet connectivity is as follows:

private bool IsInternetAvailable()
{
    try
    {
        Dns.GetHostEntry("www.google.com"); //using System.Net;
        return true;
    } catch (SocketException ex) {
        return false;
    }
}

The above code can be found (in VB.Net by reading the comment from Joacim Andersson [MVP]) in the following post.

Note: The latest edit was suggested by AceInfinity but was rejected in community review. My reputation is too low to override this so I made the change myself.

Answer 4

From msdn:

There are many cases in which a device or computer is not connected to a useful network but is still considered available and GetIsNetworkAvailable will return true.

One of these examples could be your case:

For example, if the device running the application is connected to a wireless network that requires a proxy, but the proxy is not set, GetIsNetworkAvailable will return true. Another example of when GetIsNetworkAvailable will return true is if the application is running on a computer that is connected to a hub or router where the hub or router has lost the upstream connection.

Answer 5

From MSDN (emphasis is mine):

A network connection is considered to be available if any network interface is marked "up" and is not a loopback or tunnel interface.

If with "connection" you mean Internet connection then you should DllImport the function InternetCheckConnection or InternetQueryOption.

Instead if what you need is just to know if computer is connected to any useful LAN the best thing you can do is to iterate network connection by yourself and to filter (using NetworkInterfaceType, IsReceiveOnly and OperationalStatus) what you're not interested too.

Answer 6

Note that we are using the Windows.Networking.Connectivity.NetworkInformation and not the System.Net.NetworkInformation namespace.

public bool checkInternetAccess()
{
    var connectivityLevel = Windows.Networking.Connectivity.NetworkInformation
                           .GetInternetConnectionProfile().GetNetworkConnectivityLevel();

    return connectivityLevel == NetworkConnectivityLevel.InternetAccess;
}

Basically what ventura8 said. I would comment his solution, mentioning the namespaces, but I lack enough reputation.