curl_exec（）不会抛出响应

Hi I have a piece of code on the client as follows:

   <?php
      $curl = curl_init();
      // Set some options - we are passing in a useragent too here
      curl_setopt_array($curl, array(
      CURLOPT_RETURNTRANSFER => 1,
      CURLOPT_URL => 'http://xx.xx.xxx.xxx:9000/postpara.php', //xx.xx.xxx.xxx is the public ip
      CURLOPT_USERAGENT => 'Codular Sample cURL Request',
      CURLOPT_POST => 1,
      CURLOPT_POSTFIELDS => array(
           item1 => 'value',
           item2 => 'value2'
           )
       ));
      // Send the request & save response to $resp
      $resp = curl_exec($curl);
      // Close request to clear up some resources
      curl_close($curl);
      echo $resp;
?>

My server code sits behind a proxy server, with the local ip = "192.168.12.23". I have done the port forwarding and the public IP xx.xx.xxx.xxx:9000 correctly points to the local ip. However I am unable to get any response from this server code. server Code is as follows:

<?php 
   $items1 = $_POST["item1"];
   $items2 = $_POST["item2"];
   print($items1 . $items2);
?>

I have tested this on a different server and it gives me output as expected. Is there any problem the proxy is creating?