use internal port

lib/loopback-listener.js

@@ -42,14 +42,14 @@ module.exports.create = function (opts) {
   process.nextTick(function () {
     results.plainServers.forEach(function (plainServer) {
       plainServer.listen(
-        plainServer.__plainPort.port
+        plainServer.__plainPort.internal || plainServer.__plainPort.port
       , plainServer.__plainPort.address || '0.0.0.0'
       , onListen
       );
     });
     results.tlsServers.forEach(function (tlsServer) {
       tlsServer.listen(
-        tlsServer.__tlsPort.port
+        tlsServer.__tlsPort.internal || tlsServer.__tlsPort.port
       , tlsServer.__tlsPort.address || '0.0.0.0'
       , onListen
       );