C++ boost::asio no connection could be made because the target machine actively refused it

Question

This is not a duplicate! (This is not about UDP, it is TCP. This is not C#, Python or whatever, it is C++)

I get the error described in the title if I try to connect through my external IP. However, it works via "localhost" or "127.0.0.1" (I am running client.exe and server.exe on the same machine). This code was copied from an example and I made minor changes.

EDIT: I gave Firewall permission to both executable files. Still, the problem persists.

Server:

#include <ctime>
#include <iostream>
#include <string>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

std::string make_daytime_string()
{
  using namespace std; // For time_t, time and ctime;
  time_t now = time(0);
  return ctime(&now);
}

int main()
{
  try
   {
    boost::asio::io_service io_service;

    tcp::acceptor acceptor(io_service, tcp::endpoint(tcp::v4(), 62000));


    for (;;)
    {
      tcp::socket socket(io_service);
      acceptor.accept(socket);

      std::string message = make_daytime_string();

      boost::system::error_code ignored_error;
      boost::asio::write(socket, boost::asio::buffer(message), ignored_error);
    }
  }
  catch (std::exception& e)
  {
     std::cerr << e.what() << std::endl;
  }

  return 0;
 }

Client:

#include <iostream>
#include <boost/array.hpp>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

int main(int argc, char* argv[])
{
  try
  {
    boost::asio::io_service io_service;
    tcp::resolver resolver(io_service);
    tcp::resolver::query query("localhost", "62000");
    tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);

    tcp::endpoint endpoint = *endpoint_iterator;
    std::cout << endpoint << "\n\n";

    tcp::socket socket(io_service);

    boost::asio::connect(socket, endpoint_iterator);

    for (;;)
    {
      boost::array<char, 128> buf;
      boost::system::error_code error;

      size_t len = socket.read_some(boost::asio::buffer(buf), error);

      if (error == boost::asio::error::eof)
        break; // Connection closed cleanly by peer.
      else if (error)
        throw boost::system::system_error(error); // Some other error.

      std::cout.write(buf.data(), len);
    }
  }
  catch (std::exception& e)
  {
     std::cerr << e.what() << std::endl;
  }

  std::cout << "\n\n";
  system("pause");
  return 0;
}

I had tried that before posting this thread. It doesn't work. — bitcode, Dec 06 '15 at 23:21
This [answer](http://stackoverflow.com/a/15036553/1053968) may be helpful. In particularly, one may need to investigate the routing devices capabilities/configuration (looping-back and port forwarding). — Tanner Sansbury, Dec 07 '15 at 15:40
@pogorskiy The code works with both localhost and 127.0.0.1. The problem is the external IP. — bitcode, Dec 08 '15 at 17:24

score 3 · Accepted Answer · answered Feb 05 '16 at 16:18

It turns out my router won't accept connections from the internet (using external IP) if the request comes from my local network.

As long as the request isn't coming from my local network, the client will connect to the server without problems.

If I want to run both client and server on my machine, I must use my internal IP (127.0.0.1 or my internal network IP).

If someone else wants to connect to my server from outside my local network, it will work fine. But machines inside my local network won't be able to access the server using external IP, only internal IP.

I never saw this happen. But at least it doesn't affect the functionality of my program.

You may want to clarify what your "external" IP is. Do you mean the ISP-assigned public IPv4 address, or a 192.168.x.x / 10.x.x.x local network address? Your router doesn't care about the latter. — MSalters, Sep 12 '17 at 10:26

C++ boost::asio no connection could be made because the target machine actively refused it

1 Answers1