diff --git a/ryu/app/gre_tunnel.py b/ryu/app/gre_tunnel.py
index 10d1f30a..3e9fbe72 100644
--- a/ryu/app/gre_tunnel.py
+++ b/ryu/app/gre_tunnel.py
@@ -400,6 +400,16 @@ class GRETunnel(app_manager.RyuApp):
             [dpset.EventDP, PortSet.EventTunnelKeyDel, PortSet.EventVMPort,
              PortSet.EventTunnelPort, ofp_event.EventOFPPacketIn])
 
+    def start(self):
+        super(GRETunnel, self).start()
+        self.port_set.start()
+
+    def stop(self):
+        app_mgr = app_manager.get_instance()
+        app_mgr.uninstantiate(self.port_set)
+        self.port_set = None
+        super(GRETunnel, self).stop()
+
     # TODO: track active vm/tunnel ports
 
     @handler.set_ev_handler(dpset.EventDP)
diff --git a/ryu/base/app_manager.py b/ryu/base/app_manager.py
index a5f1c4cf..21e129b5 100644
--- a/ryu/base/app_manager.py
+++ b/ryu/base/app_manager.py
@@ -64,6 +64,11 @@ class RyuApp(object):
         self.events = hub.Queue(128)
         self.replies = hub.Queue()
         self.logger = logging.getLogger(self.name)
+
+    def start(self):
+        """
+        Hook that is called after startup initialization is done.
+        """
         self.threads.append(hub.spawn(self._event_loop))
 
     def register_handler(self, ev_cls, handler):
@@ -240,6 +245,9 @@ class AppManager(object):
             for ev_cls in i.event_handlers.keys():
                 LOG.debug("  CONSUMES %s" % (ev_cls.__name__,))
 
+        for app in self.applications.values():
+            app.start()
+
     def close(self):
         def close_all(close_dict):
             for app in close_dict.values():