Detect Changes in Network Connectivity

Some times you will need a mechanism to check whether changes to network occurring during running your application.
So as a solution for this you can add handlers to the static NetworkAddressChanged and NetworkAvailabilityChanged events implemented by theSystem.Net.NetworkInformation.NetworkChange class.

Souce Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.NetworkInformation;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            // Add the handlers to the NetworkChange events.
            NetworkChange.NetworkAvailabilityChanged +=
            NetworkAvailabilityChanged;
            NetworkChange.NetworkAddressChanged +=
            NetworkAddressChanged;

Console.ReadLine();
        }

// Declare a method to handle NetworkAvailabilityChanged events.
        private static void NetworkAvailabilityChanged(
        object sender, NetworkAvailabilityEventArgs e)
        {
            // Report whether the network is now available or unavailable.
            if (e.IsAvailable)
            {
                Console.WriteLine("Network Available");
            }
            else
            {
                Console.WriteLine("Network Unavailable");
            }
        }
        // Declare a method to handle NetworkAdressChanged events.
        private static void NetworkAddressChanged(object sender, EventArgs e)
        {
            Console.WriteLine("Current IP Addresses:");
            // Iterate through the interfaces and display information.
            foreach (NetworkInterface ni in
            NetworkInterface.GetAllNetworkInterfaces())
            {
                foreach (UnicastIPAddressInformation addr
                in ni.GetIPProperties().UnicastAddresses)
                {
                    Console.WriteLine(" - {0} (lease expires {1})",
                    addr.Address, DateTime.Now +
                    new TimeSpan(0, 0, (int)addr.DhcpLeaseLifetime));
                }
            }
        }
    }
}

http://www.codeproject.com/Articles/206720/Simple-Network-Status-Monitor-Example