How to check whether you are connected to Internet or not in C#?

There are several ways to check whether a machine is connected to the internet in C#. The most common approach uses the System.Net namespace, which provides methods for sending and receiving data from resources identified by a URI. The WebClient or HttpClient classes are particularly useful for this purpose.

The technique involves making a request to a reliable URL and checking if the response is successful. Google's http://google.com/generate_204 endpoint is commonly used because it returns a minimal response, making it efficient for connectivity checks.

Using WebClient for Internet Connectivity Check

Example

using System;
using System.Net;

class Program {
    static void Main(string[] args) {
        if (IsConnectedToInternet()) {
            Console.WriteLine("Connected to the internet");
        } else {
            Console.WriteLine("No internet connection");
        }
    }

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

The output of the above code is −

Connected to the internet

Using HttpClient for Modern Applications

For modern .NET applications, HttpClient is preferred over WebClient as it provides better performance and async support −

Example

using System;
using System.Net.Http;
using System.Threading.Tasks;

class Program {
    static async Task Main(string[] args) {
        bool isConnected = await IsConnectedToInternetAsync();
        Console.WriteLine(isConnected ? "Internet connection available" : "No internet connection");
    }

    public static async Task<bool> IsConnectedToInternetAsync() {
        try {
            using (var client = new HttpClient()) {
                client.Timeout = TimeSpan.FromSeconds(5);
                var response = await client.GetAsync("http://google.com/generate_204");
                return response.IsSuccessStatusCode;
            }
        }
        catch {
            return false;
        }
    }
}

The output of the above code is −

Internet connection available

Using NetworkAvailabilityChanged Event

For applications that need to monitor connectivity changes continuously, you can use the NetworkAvailabilityChanged event −

Example

using System;
using System.Net;
using System.Net.NetworkInformation;

class Program {
    static void Main(string[] args) {
        NetworkChange.NetworkAvailabilityChanged += NetworkChange_NetworkAvailabilityChanged;
        
        Console.WriteLine("Initial connectivity: " + (NetworkInterface.GetIsNetworkAvailable() ? "Available" : "Not Available"));
        Console.WriteLine("Monitoring network changes...");
        
        // Keep the application running for demonstration
        System.Threading.Thread.Sleep(10000);
    }

    private static void NetworkChange_NetworkAvailabilityChanged(object sender, NetworkAvailabilityEventArgs e) {
        Console.WriteLine("Network availability changed: " + (e.IsAvailable ? "Available" : "Not Available"));
    }
}

The output of the above code is −

Initial connectivity: Available
Monitoring network changes...

Comparison of Methods

Conclusion

Checking internet connectivity in C# can be accomplished through various methods, with HttpClient being the preferred modern approach for its async capabilities and better performance. For real-time monitoring, combine NetworkInterface checks with actual HTTP requests to reliable endpoints like Google's generate_204 service.