public static bool IsNetAvailable(string ip)
{
    System.Net.NetworkInformation.Ping ping = new System.Net.NetworkInformation.Ping();
    System.Net.NetworkInformation.PingReply pingStatus = ping.Send(IPAddress.Parse(ip), 3000);

    if (pingStatus.Status == System.Net.NetworkInformation.IPStatus.Success)
    {
        return true;
    }
    else
    {
        return false;
    }
}

static void Main(string[] args)
{
    Console.WriteLine(IsNetAvailable("192.168.0.66"));
    Console.WriteLine(IsNetAvailable("192.168.0.67"));
    Console.ReadKey();
}