class NetworkManager
    {
        private const string ipBase = "10.0.0.";
        private const bool resolveNames = true;

        private ConcurrentBag<Host> bag = new ConcurrentBag<Host>();
        private CountdownEvent countdown;
        private int upCount = 0;
        private object lockObj = new object();

        public void ping()
        {
            ping(ipBase);
        }

        public void ping(string ipBase)
        {
            countdown = new CountdownEvent(1);
            Stopwatch sw = new Stopwatch();
            sw.Start();
            for (int i = 1; i < 255; i++)
            {
                string ip = ipBase + i.ToString();

                Ping p = new Ping();
                p.PingCompleted += new PingCompletedEventHandler(p_PingCompleted);
                countdown.AddCount();
                p.SendAsync(ip, 1000, ip);
            }
            countdown.Signal();
            countdown.Wait();
            sw.Stop();
            TimeSpan span = new TimeSpan(sw.ElapsedTicks);
            Console.WriteLine("Took {0} milliseconds. {1} hosts active.", sw.ElapsedMilliseconds, upCount);
            foreach (Host h in bag)
            {
                Console.WriteLine(h.Name);
            }
            Console.ReadLine();
        }

        private void p_PingCompleted(object sender, PingCompletedEventArgs e)
        {
            string ip = (string)e.UserState;
            if (e.Reply != null && e.Reply.Status == IPStatus.Success)
            {
                if (resolveNames)
                {
                    string name;
                    try
                    {
                        IPHostEntry hostEntry = Dns.GetHostEntry(ip);
                        name = hostEntry.HostName;
                    }
                    catch (SocketException ex)
                    {
                        name = "?";
                    }
                    Console.WriteLine("{0} ({1}) is up: ({2} ms)", ip, name, e.Reply.RoundtripTime);
                    bag.Add(new Host(ip, "mac", name));
                }
                else
                {
                    Console.WriteLine("{0} is up: ({1} ms)", ip, e.Reply.RoundtripTime);
                    bag.Add(new Host(ip, "mac", ""));
                }
                lock (lockObj)
                {
                    upCount++;
                }
            }
            else if (e.Reply == null)
            {
                Console.WriteLine("Pinging {0} failed. (Null Reply object?)", ip);
            }
            countdown.Signal();
        }
    }