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c # punch NAT network with TCP / IP protocol

Punching the UDP network works and works. However, when it comes to TCP, it's possible that I'm writing something wrong but I'm not a beginner programmer, or maybe I don't understand something.
Of course, I'll shorten a bit, we assume that we already have something as trivial as connection to an external server :)
Packet synchronization between threads as well as their creation, queuing, serialization, sending raw bytes and much more I skip because it is about the element of creating TCP sockets and not what works.
We will use the TcpListener class for the server.
public void InitializeServer(IPAddress address, int port)
{
try
{
// 127.0.0.1 accept only local connections, 0.0.0.0 is open for whole internet connections
listener = new TcpListener(address, port);
socket = listener.Server;
// Enable NAT Translation
listener.AllowNatTraversal(true);
// Start listening for example 10 client requests.
listener.Start(listenQueue);
Debug.Log($"[L{socket.LocalEndPoint}]Server start... ", EDebugLvl.Log);
OnServerInitialize(true);
// Enter the listening loop.
StartListener();
}
catch (SocketException e)
{
Debug.LogError($"SocketException: {e}", EDebugLvl.Error);
OnServerInitialize(false);
}
}
We start listening
private void StartListener()
{
Debug.Log("\nWaiting for a connection... ");
listener.BeginAcceptTcpClient(AcceptCallback, listener);
}
When the server receives the connection, we create a new socket
private void AcceptCallback(IAsyncResult ar)
{
TcpListener server = (TcpListener)ar.AsyncState;
TcpClient newClient = null;
try
{
newClient = server.EndAcceptTcpClient(ar);
}
catch (Exception e)
{
Debug.LogError(e.ToString());
}
if (newClient != null && newClient.Connected)
{
//...
client.StartRead();
}
//Loop
StartListener();
}
We create a new socket at the client and try to establish a connection
public void Connect(IPEndPoint remote, IPEndPoint bind = null, bool reuseAddress = false)
{
if (bind == null)
{
client = new TcpClient();
}
else
{
client = new TcpClient(bind);
}
socket = client.Client;
if (reuseAddress)
{
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, reuseAddress);
//It throws me a error SocketOption so im comment this.
//socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseUnicastPort, reuseAddress);
}
client.BeginConnect(remote.Address, remote.Port, ConnectCallback, null);
}
The connection works without any problems and data transfer.
Unfortunately, here as we know, we must start a new socket listening on the same address and port that was created when connecting to the server. I do this for every client.
public void StartHost(Client server)
{
if (server != null && server.socket.Connected)
{
IPEndPoint localHost = (IPEndPoint)server.socket.LocalEndPoint;
InitializeHost(localHost.Address, localHost.Port);
}
}
public void InitializeHost(IPAddress address, int port, bool reuse = false)
{
try
{
listener = new TcpListener(address, port);
socket = listener.Server;
if (reuse)
{
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseUnicastPort, true);
}
// Enable NAT Translation
listener.AllowNatTraversal(true);
// Start listening for example 10 client requests.
listener.Start(listenQueue);
Debug.Log($"\n[L{socket.LocalEndPoint}]Host start... ", EDebugLvl.Log);
OnServerInitialize(true);
// Enter the listening loop.
StartListener();
}
catch (SocketException e)
{
Debug.LogError($"SocketException: {e}", EDebugLvl.Error);
OnServerInitialize(false);
}
}
private void StartListener()
{
Debug.Log("\nWaiting for a connection... ");
listener.BeginAcceptTcpClient(AcceptCallback, listener);
}
private void AcceptCallback(IAsyncResult ar)
{
TcpListener server = (TcpListener)ar.AsyncState;
TcpClient newClient = null;
try
{
newClient = server.EndAcceptTcpClient(ar);
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
if (newClient != null && newClient.Connected)
{
//...
client.StartRead();
}
//Loop
StartListener();
}
So, as they write everywhere ... client "B" sends a packet to the server that wants to establish a connection, the server sends information to the client "A" about the client "B" and vice versa
Then they both try to connect with the new socket? No problem...
public void Connect(IPEndPoint remote, IPEndPoint bind = null, bool reuseAddress = false)
{
if (bind == null)
{
client = new TcpClient();
}
else
{
client = new TcpClient(bind);
}
socket = client.Client;
if (reuseAddress)
{
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, reuseAddress);
//socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseUnicastPort, reuseAddress);
}
client.BeginConnect(remote.Address, remote.Port, ConnectCallback, null);
}
private void ConnectCallback(IAsyncResult ar)
{
try
{
client.EndConnect(ar);
}
catch (Exception e)
{
Debug.LogError(e.ToString(), EDebugLvl.ConnectionError);
}
if (client.Connected)
{
Debug.Log($"[P{socket.RemoteEndPoint}, L{socket.LocalEndPoint}]Connected", EDebugLvl.ConnectionLog);
stream = new NetworkStream(socket, FileAccess.ReadWrite, true);
StartRead();
}
ConnectedComplete(this, socket.Connected);
}
No matter how many times I try, the connection is rejected ... the addresses match everywhere and yet it does not work, so I have nothing to write about in this case, especially since UDP works for me.
What I wrote only works on the same NAT network. Unfortunately, I noticed that on the same NAT created two connections. One is the result of trying to connect the new socket A to B and the other is the result of receiving a new connection from B to A, so each client has one unnecessary socket connected by a local address. So all NAT TCP / IP Punch NAT doesn't work for me. I can actually use UDP but I really need TCP. I have been sitting on it for several months in my free time but nowhere can I find an example from the code and not the theory of which there is a lot.
I accumulated a lot of knowledge for 8 years and from 2 I write applications using sockets and finally I need to punch the net.
Why won't I use the ready solution? I need my own which is fully open using only UDP and TCP because some target devices only support these protocols. I also used the Socket class but this one did not give me a working copy.
Maybe someone will be able to help me for which I would be very grateful and certainly the post will also help others understand this.
Regards
Octavian

NAT hole punching only works with UDP, and even that is a hack.
NAT firewall implementations will start tracking a TCP stream when they see the initial SYN packet leaving the network. To capture incoming TCP streams you need to create an incoming rule on the router, there's no way around this. If the router supports UPnP, you can ask it to create that rule for you dynamically.
Since UDP doesn't have a SYN packet equivalent, routers will start tracking the stream on any outgoing packet. This is why NAT hole punching works. If both end points are behind NAT and just assume that the link will work. Both can just start sending UDP packets to each other. The routers will add the connection state, and map the incoming packets to each endpoint.

How can I make a TCP Server automatically reconnect to a client? C#

Below is my code for the TCP server side. The problem is when the app on client machine closes, the server can't automically try to reconnect every 2 seconds until connected. How can I achieve that?
My idea is after connected to the client, server creates a status thread to send a byte to that client every 30s, if fail ---> terminate connection and retry to connect again. I'm not sure if its gonna work.
public static TcpClient client = new TcpClient();
public static int port = 6446;
public static string connectTo = "192.168.0.11";
public static NetworkStream dataStream;
static void Main(string[] args)
{
int retry = 0;
TryingConnect:
try
{
do
{
if (retry == 10)
{
retry = 0;
Console.Clear();
}
cout("Connecting...");
IPAddress ipAddress = IPAddress.Parse(connectTo);
client.Connect(ipAddress, port);
} while (client.Connected != true);
cout("Connected!");
dataStream = client.GetStream();
}
catch (Exception ex)
{
// Debug: MessageBox.Show(ex.ToString());
retry++;
Thread.Sleep(2000);
goto TryingConnect;
}
}

A server is the communication party which listen for connections from clients. A client is the one which initiates the connection. If you would like to server to recreate a lost connection to the client the server would actually be the client in this case because it initiates a new connection.
Apart from the meaning of the words client and server: if peer C likes S to connect to it C must be first listen and accept incoming connections, which is not the case for the common client. Even if C would do this the network of C must actually be reachable by S to create a new connection. This is often not the case, i.e if C is located in some local network (typical setup at home, work and often on mobile phone) then C is not reachable by S while C itself could reach S. Therefore S could not make a connection back to C.

C# Server - Socket not connecting and out of memory exception

I am trying to implement a simple TCP server and I basically copied the example on MSDN sans a couple of lines and tried to make it work. I have an external client trying to connect already.
This is my code:
IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName());
IPEndPoint localEP = new IPEndPoint(ipHostInfo.AddressList[0], 4001);
Socket listener = new Socket(localEP.Address.AddressFamily,
SocketType.Stream, ProtocolType.Tcp);
try
{
listener.Bind(localEP);
listener.Listen(1000);
while (true)
{
listener.BeginAccept(new AsyncCallback(AcceptCnxCallback), listener);
}
}
catch (Exception e)
{
//Log here
}
This is my callback:
private void AcceptCnxCallback(IAsyncResult iar)
{
MensajeRecibido msj = new MensajeRecibido();
Socket server = (Socket)iar.AsyncState;
msj.workSocket = server.EndAccept(iar);
}
And this is the information of one of the incoming packages:
TCP:[SynReTransmit #1727889]Flags=......S., SrcPort=57411, DstPort=4001, PayloadLen=0, Seq=673438964, Ack=0, Win=5840 ( Negotiating scale factor 0x4 ) = 5840
Source: 10.0.19.65 Destination: 10.0.19.59
I basically have two issues:
If I use the while loop I get an OutOfMemoryException
I never do manage to connect to the client
Any tips on either of the two problems? Thank you in advance!

Your problem is, that you use asynchronous calls all the time. There is no wait mechanism or similar, so generally you are just creating new asynchronous callbacks in an infinite loop.
For a basic TCP I would recommend to use the simple approach and use the synchronous methods.
Accept() is blocking, so the program flow will stop until there is an ingoing connection.
while (true)
{
Socket s = listener.Accept();
buffer = new byte[BUFFER_SIZE];
s.Receive(buffer);
//Do something
s.Send(...);
}
Noe that this is just a basic example. If you want to keep your connection you might consider a new Thread for each accepted Socket, that continoues with receiving and sending data.

First problem
You are using an infinite loop to call an async method.
try it like this:
listener.BeginAccept(new AsyncCallback(AcceptCnxCallback), listener);
//add your code here (this part will be executed wile the listner is waiting for a connection.
while (true)
{
Thread.Sleep(100);
}
and change the Callbackmethod to:
private void AcceptCnxCallback(IAsyncResult iar)
{
MensajeRecibido msj = new MensajeRecibido();
Socket server = (Socket)iar.AsyncState;
msj.workSocket = server.EndAccept(iar);
//call again the listener after you get a message
listener.BeginAccept(new AsyncCallback(AcceptCnxCallback), listener);
}

TcpConnection capable of handling concurrent requests. Client-Server

I'm trying to build a simple Client-Server Application with the following codes:
//SERVER
IPAddress ipAd = IPAddress.Parse("192.163.10.101");
TcpListener myList = new TcpListener(ipAd, 8001);
myList.Start();
Console.WriteLine("The server is running at port 8001...");
Console.WriteLine("The local End point is :" + myList.LocalEndpoint);
Console.WriteLine("Waiting for a connection.....");
Socket s = myList.AcceptSocket();
Console.WriteLine("Connection accepted from " + s.RemoteEndPoint);
//CLIENT
TcpClient tcpclnt = new TcpClient();
Console.WriteLine("Connecting.....");
tcpclnt.Connect("192.163.10.101",8001);
Console.WriteLine("Connected");
this actually does what I need wherein the client can connect to the server. However, when I try to run multiple instances of the client to connect with the server, the server only accepts the first client to connect. Meaning there's like a one-to-one connection wherein only one client can connect with the client. However, what I need is to give the server the ability to accept connections from more than one client.
If anyone can point me a possible solution to this, I'll really be appreciative! Thanks!

You need to call AcceptSocket again to accept another socket.
A typical design would be to have to call BeginAcceptSocket and in the callback call EndAcceptSocket, dispatch the client processing to its own thread (or a worker thread using async methods) and then call BeginAcceptSocket again.
This fragment is untested but should be more or less right/ get you thinking in the right direction.
class Server
{
public Server()
{
TcpListener listener = null;
// init the listener
listener.BeginAcceptSocket((ar) => AcceptLoop(ar, listener),null);
}
public void HandleClientSocketRead(IAsyncResult ar, byte[] recvBuffer, Socket clientSocket)
{
int recvd = clientSocket.EndReceive(ar);
//do something with the data
clientSocket.BeginReceive(recvBuffer, 0, 1024, SocketFlags.None, (ar2) => HandleClientSocketRead(ar2, recvBuffer, clientSocket), null);
}
public void AcceptLoop(IAsyncResult ar, TcpListener listener)
{
Socket clientSocket = listener.EndAcceptSocket(ar); // note that this can throw
byte[] recvBuffer = new byte[1024];
clientSocket.BeginReceive(recvBuffer, 0, 1024, SocketFlags.None, (ar2) => HandleClientSocketRead(ar2, recvBuffer, clientSocket), null);
listener.BeginAcceptSocket((ar) => AcceptLoop(ar, listener), null);
}
}

If you are looking to write a server, a good design is to have a [server].exe and a [client].exe. The [server].exe, will of course accept and process all incoming connections, maintain the client sockets, and perform whatever actions you need. Below is a very basic example on writing a server to accept multiple client sockets, and store them in a List object. This, however, is not multithreaded so the code, does block.
[server].exe
//-----------------------------------------------------------------------------
// <copyright file="Program.cs" company="DCOM Productions">
// Copyright (c) DCOM Productions. All rights reserved.
// </copyright>
//-----------------------------------------------------------------------------
namespace MultiSocketServerExample {
using System;
using System.Net.Sockets;
using System.Net;
using System.Collections.Generic;
class Program {
static List<Socket> m_ConnectedClients = new List<Socket>();
static void Main(string[] args) {
Socket host = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
host.Bind(new IPEndPoint(IPAddress.Any, 9999));
host.Listen(1);
while (true) {
m_ConnectedClients.Add(host.Accept());
Console.WriteLine("A client connected.");
}
}
}
}
Then to work with your clients: (Again, very basic example)
m_ConnectedClients[0].Send(Encoding.ASCII.GetBytes("hello!");
Network programming with the Socket class is a lot easier in my opinion then using TcpListener and TcpClient. The reason I say this is that it is already a really good and easy to use implementation, and by using TcpListener and TcpClient where they create further abstraction, lessenes your ability to understand what is going on (in my opinion).

getting 10060 (Connection Timed Out) when stress testing simple tcp server

I have created simple tcp server - it works pretty well.
the problems starts when we switch to the stress tests -since our server should handle many concurrent open sockets - we have created a stress test to check this.
unfortunately, looks like the server is choking and can not respond to new connection request in timely fashion when the number of the concurrent open sockets are around 100.
we already tried few types of server - and all produce the same behavior.
the server: can be something like the samples in this post(all produce the same behavior)
How to write a scalable Tcp/Ip based server
here is the code that we are using - when a client connects - the server will just hang in order to keep the socket alive.
enter code here
public class Server
{
private static readonly TcpListener listener = new TcpListener(IPAddress.Any, 2060);
public Server()
{
listener.Start();
Console.WriteLine("Started.");
while (true)
{
Console.WriteLine("Waiting for connection...");
var client = listener.AcceptTcpClient();
Console.WriteLine("Connected!");
// each connection has its own thread
new Thread(ServeData).Start(client);
}
}
private static void ServeData(object clientSocket)
{
Console.WriteLine("Started thread " + Thread.CurrentThread.ManagedThreadId);
var rnd = new Random();
try
{
var client = (TcpClient)clientSocket;
var stream = client.GetStream();
byte[] arr = new byte[1024];
stream.Read(arr, 0, 1024);
Thread.Sleep(int.MaxValue);
}
catch (SocketException e)
{
Console.WriteLine("Socket exception in thread {0}: {1}", Thread.CurrentThread.ManagedThreadId, e);
}
}
}
the stress test client: is a simple tcp client, that loop and open sokets, one after the other
class Program
{
static List<Socket> sockets;
static private void go(){
Socket newsock = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
IPEndPoint iep = new IPEndPoint(IPAddress.Parse("11.11.11.11"), 2060);
try
{
newsock.Connect(iep);
}
catch (SocketException ex)
{
Console.WriteLine(ex.Message );
}
lock (sockets)
{
sockets.Add(newsock);
}
}
static void Main(string[] args)
{
sockets = new List<Socket>();
//int start = 1;// Int32.Parse(Console.ReadLine());
for (int i = 1; i < 1000; i++)
{
go();
Thread.Sleep(200);
}
Console.WriteLine("press a key");
Console.ReadKey();
}
}
}
is there an easy way to explain this behavior? maybe c++ implementation if the TCP server will produce better results? maybe it is actually a client side problem?
Any comment will be welcomed !
ofer

Specify a huge listener backlog: http://msdn.microsoft.com/en-us/library/5kh8wf6s.aspx

Firstly a thread per connection design is unlikely to be especially scalable, you would do better to base your design on an asynchronous server model which uses IO Completion Ports under the hood. This, however, is unlikely to be the problem in this case as you're not really stressing the server that much.
Secondly the listen backlog is a red herring here. The listen backlog is used to provide a queue for connections that are waiting to be accepted. In this example your client uses a synchronous connect call which means that the client will never have more than 1 connect attempt outstanding at any one time. If you were using asynchronous connection attempts in the client then you would be right to look at tuning the listen backlog, perhaps.
Thirdly, given that the client code doesn't show that it sends any data, you can simply issue the read calls and remove the sleep that follows it, the read calls will block. The sleep just confuses matters.
Are you running the client and the server on the same machine?
Is this ALL the code in both client and server?
You might try and eliminate the client from the problem space by using my free TCP test client which is available here: http://www.lenholgate.com/blog/2005/11/windows-tcpip-server-performance.html
Likewise, you could test your test client against one of my simple free servers, like this one: http://www.lenholgate.com/blog/2005/11/simple-echo-servers.html
I can't see anything obviously wrong with the code (apart from the overall design).