我个人觉得Anton和moffeltje的答案最好，但我增加了一个检查，排除VMWare和其他公司设置的虚拟网络。

public static bool IsAvailableNetworkActive()
{
    // only recognizes changes related to Internet adapters
    if (!System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable()) return false;

    // however, this will include all adapters -- filter by opstatus and activity
    NetworkInterface[] interfaces = System.Net.NetworkInformation.NetworkInterface.GetAllNetworkInterfaces();
    return (from face in interfaces
            where face.OperationalStatus == OperationalStatus.Up
            where (face.NetworkInterfaceType != NetworkInterfaceType.Tunnel) && (face.NetworkInterfaceType != NetworkInterfaceType.Loopback)
            where (!(face.Name.ToLower().Contains("virtual") || face.Description.ToLower().Contains("virtual")))
            select face.GetIPv4Statistics()).Any(statistics => (statistics.BytesReceived > 0) && (statistics.BytesSent > 0));
}

你绝对没有办法可靠地检查是否有互联网连接(我想你的意思是访问互联网)。

但是，您可以请求几乎从未离线的资源，例如ping google.com或类似的东西。我认为这是有效的。

try { 
    Ping myPing = new Ping();
    String host = "google.com";
    byte[] buffer = new byte[32];
    int timeout = 1000;
    PingOptions pingOptions = new PingOptions();
    PingReply reply = myPing.Send(host, timeout, buffer, pingOptions);
    return (reply.Status == IPStatus.Success);
}
catch (Exception) {
    return false;
}

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

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

多线程版本的ping:

  using System;
  using System.Collections.Generic;
  using System.Diagnostics;
  using System.Net.NetworkInformation;
  using System.Threading;


  namespace OnlineCheck
  {
      class Program
      {

          static bool isOnline = false;

          static void Main(string[] args)
          {
              List<string> ipList = new List<string> {
                  "1.1.1.1", // Bad ip
                  "2.2.2.2",
                  "4.2.2.2",
                  "8.8.8.8",
                  "9.9.9.9",
                  "208.67.222.222",
                  "139.130.4.5"
                  };

              int timeOut = 1000 * 5; // Seconds


              List<Thread> threadList = new List<Thread>();

              foreach (string ip in ipList)
              {

                  Thread threadTest = new Thread(() => IsOnline(ip));
                  threadList.Add(threadTest);
                  threadTest.Start();
              }

              Stopwatch stopwatch = Stopwatch.StartNew();

              while (!isOnline && stopwatch.ElapsedMilliseconds <= timeOut)
              {
                   Thread.Sleep(10); // Cooldown the CPU
              }

              foreach (Thread thread in threadList)
              { 
                  thread.Abort(); // We love threads, don't we?
              }


              Console.WriteLine("Am I online: " + isOnline.ToYesNo());
              Console.ReadKey();
          }

          static bool Ping(string host, int timeout = 3000, int buffer = 32)
          {
              bool result = false;

              try
              {
                  Ping ping = new Ping();                
                  byte[] byteBuffer = new byte[buffer];                
                  PingOptions options = new PingOptions();
                  PingReply reply = ping.Send(host, timeout, byteBuffer, options);
                  result = (reply.Status == IPStatus.Success);
              }
              catch (Exception ex)
              {

              }

              return result;
          }

          static void IsOnline(string host)
          {
              isOnline =  Ping(host) || isOnline;
          }
      }

      public static class BooleanExtensions
      {
          public static string ToYesNo(this bool value)
          {
              return value ? "Yes" : "No";
          }
      }
  }

使用NetworkMonitor监控网络状态和internet连接。

示例:

namespace AmRoNetworkMonitor.Demo
{
    using System;

    internal class Program
    {
        private static void Main()
        {
            NetworkMonitor.StateChanged += NetworkMonitor_StateChanged;
            NetworkMonitor.StartMonitor();

            Console.WriteLine("Press any key to stop monitoring.");
            Console.ReadKey();
            NetworkMonitor.StopMonitor();

            Console.WriteLine("Press any key to close program.");
            Console.ReadKey();
        }

        private static void NetworkMonitor_StateChanged(object sender, StateChangeEventArgs e)
        {
            Console.WriteLine(e.IsAvailable ? "Is Available" : "Is Not Available");
        }
    }
}

尽量避免通过捕获异常来测试连接。因为我们真的预料到有时我们可能会失去网络连接。

 if (NetworkInterface.GetIsNetworkAvailable() &&
     new Ping().Send(new IPAddress(new byte[] { 8, 8, 8, 8 }),2000).Status == IPStatus.Success)
 //is online
 else
 //is offline