diff --git a/ryu/topology/event.py b/ryu/topology/event.py
index c54152b..e7b682c 100644
--- a/ryu/topology/event.py
+++ b/ryu/topology/event.py
@@ -41,6 +41,11 @@ class EventSwitchLeave(EventSwitchBase):
         super(EventSwitchLeave, self).__init__(switch)
 
 
+class EventSwitchReconnected(EventSwitchBase):
+    def __init__(self, switch):
+        super(EventSwitchReconnected, self).__init__(switch)
+
+
 class EventPortBase(event.EventBase):
     def __init__(self, port):
         super(EventPortBase, self).__init__()
diff --git a/ryu/topology/switches.py b/ryu/topology/switches.py
index 5fe5d26..1b37983 100644
--- a/ryu/topology/switches.py
+++ b/ryu/topology/switches.py
@@ -495,6 +495,7 @@ class Switches(app_manager.RyuApp):
     OFP_VERSIONS = [ofproto_v1_0.OFP_VERSION, ofproto_v1_2.OFP_VERSION,
                     ofproto_v1_3.OFP_VERSION, ofproto_v1_4.OFP_VERSION]
     _EVENTS = [event.EventSwitchEnter, event.EventSwitchLeave,
+               event.EventSwitchReconnected,
                event.EventPortAdd, event.EventPortDelete,
                event.EventPortModify,
                event.EventLinkAdd, event.EventLinkDelete,
@@ -547,8 +548,9 @@ class Switches(app_manager.RyuApp):
 
     def _unregister(self, dp):
         if dp.id in self.dps:
-            del self.dps[dp.id]
-            del self.port_state[dp.id]
+            if (self.dps[dp.id] == dp):
+                del self.dps[dp.id]
+                del self.port_state[dp.id]
 
     def _get_switch(self, dpid):
         if dpid in self.dps:
@@ -602,16 +604,18 @@ class Switches(app_manager.RyuApp):
         if ev.state == MAIN_DISPATCHER:
             dp_multiple_conns = False
             if dp.id in self.dps:
-                LOG.warning('multiple connections from %s', dpid_to_str(dp.id))
+                LOG.warning('Multiple connections from %s', dpid_to_str(dp.id))
                 dp_multiple_conns = True
+                (self.dps[dp.id]).close()
 
             self._register(dp)
             switch = self._get_switch(dp.id)
             LOG.debug('register %s', switch)
 
-            # Do not send event while dp has multiple connections.
             if not dp_multiple_conns:
                 self.send_event_to_observers(event.EventSwitchEnter(switch))
+            else:
+                self.send_event_to_observers(event.EventSwitchReconnected(switch))
 
             if not self.link_discovery:
                 return
@@ -665,19 +669,23 @@ class Switches(app_manager.RyuApp):
             # dp.id is None when datapath dies before handshake
             if dp.id is None:
                 return
+
             switch = self._get_switch(dp.id)
-            self._unregister(dp)
-            LOG.debug('unregister %s', switch)
-            self.send_event_to_observers(event.EventSwitchLeave(switch))
+            if switch:
+                if (dp == switch.dp):
+                    self._unregister(dp)
+                    LOG.debug('unregister %s', switch)
 
-            if not self.link_discovery:
-                return
+                    self.send_event_to_observers(event.EventSwitchLeave(switch))
 
-            for port in switch.ports:
-                if not port.is_reserved():
-                    self.ports.del_port(port)
-                    self._link_down(port)
-            self.lldp_event.set()
+                    if not self.link_discovery:
+                        return
+
+                    for port in switch.ports:
+                        if not port.is_reserved():
+                            self.ports.del_port(port)
+                            self._link_down(port)
+                    self.lldp_event.set()
 
     @set_ev_cls(ofp_event.EventOFPPortStatus, MAIN_DISPATCHER)
     def port_status_handler(self, ev):
@@ -762,7 +770,7 @@ class Switches(app_manager.RyuApp):
         try:
             src_dpid, src_port_no = LLDPPacket.lldp_parse(msg.data)
         except LLDPPacket.LLDPUnknownFormat as e:
-            # This handler can receive all the packtes which can be
+            # This handler can receive all the packets which can be
             # not-LLDP packet. Ignore it silently
             return