What is the best way to check for Internet connectivity using .NET?

Question

What is the fastest and most efficient way to check for Internet connectivity in .NET?

Answer 1

You can use NetworkInterface.GetIsNetworkAvailable method which indicates whether any network connection is available.

Try this:

bool connection = NetworkInterface.GetIsNetworkAvailable();
if (connection == true)
 {
     MessageBox.Show("The system is online");
 }
 else {
     MessageBox.Show("The system is offline";
 }

Answer 2

bool bb = System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable();

if (bb == true)
    MessageBox.Show("Internet connections are available");
else
    MessageBox.Show("Internet connections are not available");

Answer 3

For my application we also test by download tiny file.

string remoteUri = "https://www.microsoft.com/favicon.ico"

WebClient myWebClient = new WebClient();

try
{
    byte[] myDataBuffer = myWebClient.DownloadData (remoteUri);
    if(myDataBuffer.length > 0) // Or add more validate. eg. checksum
    {
        return true;
    }
}
catch
{
    return false;
}

Also. Some ISP may use middle server to cache file. Add random unused parameter eg. https://www.microsoft.com/favicon.ico?req=random_number Can prevent caching.

Answer 4

public static bool HasConnection()
{
    try
    {
        System.Net.IPHostEntry i = System.Net.Dns.GetHostEntry("www.google.com");
        return true;
    }
    catch
    {
        return false;
    }
}

That works

Answer 5

Something like this should work.

System.Net.WebClient

public static bool CheckForInternetConnection()
{
    try
    {
        using (var client = new WebClient())
            using (client.OpenRead("http://google.com/generate_204")) 
                return true; 
    }
    catch
    {
        return false;
    }
}

Answer 6

Here's how it is implemented in Android.

As a proof of concept, I translated this code to C#:

var request = (HttpWebRequest)WebRequest.Create("http://g.cn/generate_204");
request.UserAgent = "Android";
request.KeepAlive = false;
request.Timeout = 1500;

using (var response = (HttpWebResponse)request.GetResponse())
{
    if (response.ContentLength == 0 && response.StatusCode == HttpStatusCode.NoContent)
    {
        //Connection to internet available
    }
    else
    {
        //Connection to internet not available
    }
}