title: Node.js can access default port, but can't access specific port
body: <pre><code>http.createServer(function(request, response){
    response.writeHead(404, {'Content-Type': 'text/plain'});
    response.write('Helloworld!');
    response.end();   
  }).listen(3000,function(){
    console.log("server listen on port::: 3000");
  });
  </code></pre>
  
  <p>Here above is a quite simple snippet run in <strong>Ubuntu</strong>.
  I can access normally by default port(80), but can't access by a specific port. 
  What I accessed is an external IP, not internal localhost.
  I can get correct response via command line of "curl x.x.x.x:3000", but I just can't open it in web browsers. 
  Anybody who can give a hint will be appreciated!!!</p>