diff --git a/dragonflow/controller/apps/dnat.py b/dragonflow/controller/apps/dnat.py
index 6a16fc8b3..2b32cad0d 100644
--- a/dragonflow/controller/apps/dnat.py
+++ b/dragonflow/controller/apps/dnat.py
@@ -314,8 +314,45 @@ class DNATApp(df_base_app.DFlowApp):
                 match=self._get_ingress_icmp_flow_match(floatingip, icmp_type),
             )
 
+    def _get_source_port_detector_match(self, floatingip):
+        match = self.parser.OFPMatch(
+            eth_type=ether.ETH_TYPE_IP,
+            ipv4_src=floatingip.floating_ip_address,
+            reg6=0,
+        )
+        return match
+
+    def _install_source_port_detector(self, floatingip):
+        parser = self.parser
+        match = self._get_source_port_detector_match(floatingip)
+        actions = [
+            parser.OFPActionSetField(reg6=floatingip.lport.unique_key),
+        ]
+
+        inst_type = self.datapath.ofproto.OFPIT_APPLY_ACTIONS
+        inst = [
+            parser.OFPInstructionActions(inst_type, actions),
+            parser.OFPInstructionGotoTable(const.L2_LOOKUP_TABLE),
+        ]
+        self.mod_flow(
+            table_id=const.EXTERNAL_INGRESS_DETECT_SOURCE_TABLE,
+            priority=const.PRIORITY_HIGH,
+            match=match,
+            inst=inst,
+        )
+
+    def _uninstall_source_port_detector(self, floatingip):
+        match = self._get_source_port_detector_match(floatingip)
+        self.mod_flow(
+            command=self.ofproto.OFPFC_DELETE_STRICT,
+            table_id=const.EXTERNAL_INGRESS_DETECT_SOURCE_TABLE,
+            priority=const.PRIORITY_HIGH,
+            match=match,
+        )
+
     def _install_ingress_nat_flows(self, floatingip):
         self._get_arp_responder(floatingip).add()
+        self._install_source_port_detector(floatingip)
         self._install_ingress_capture_flow(floatingip)
         self._install_ingress_translate_flow(floatingip)
         self._install_ingress_icmp_flows(floatingip)
@@ -325,6 +362,7 @@ class DNATApp(df_base_app.DFlowApp):
         self._uninstall_ingress_capture_flow(floatingip)
         self._uninstall_ingress_translate_flow(floatingip)
         self._uninstall_ingress_icmp_flows(floatingip)
+        self._uninstall_source_port_detector(floatingip)
 
     def _get_dnat_egress_match(self, floatingip, **kwargs):
         return self.parser.OFPMatch(
diff --git a/dragonflow/controller/apps/provider.py b/dragonflow/controller/apps/provider.py
index 07002e702..fd3d01633 100644
--- a/dragonflow/controller/apps/provider.py
+++ b/dragonflow/controller/apps/provider.py
@@ -112,6 +112,11 @@ class ProviderApp(df_base_app.DFlowApp):
 
     def switch_features_handler(self, ev):
         self._setup_physical_bridges(self.bridge_mappings)
+        self.add_flow_go_to_table(
+            const.EXTERNAL_INGRESS_DETECT_SOURCE_TABLE,
+            const.PRIORITY_DEFAULT,
+            const.L2_LOOKUP_TABLE
+        )
 
     @df_base_app.register_event(l2.LogicalPort, l2.EVENT_BIND_LOCAL)
     def _add_local_port(self, lport):
@@ -286,7 +291,8 @@ class ProviderApp(df_base_app.DFlowApp):
         action_inst = self.parser.OFPInstructionActions(
             self.ofproto.OFPIT_APPLY_ACTIONS, actions)
 
-        goto_inst = self.parser.OFPInstructionGotoTable(const.L2_LOOKUP_TABLE)
+        goto_inst = self.parser.OFPInstructionGotoTable(
+            const.EXTERNAL_INGRESS_DETECT_SOURCE_TABLE)
 
         inst = [action_inst, goto_inst]
         self.mod_flow(
diff --git a/dragonflow/controller/common/constants.py b/dragonflow/controller/common/constants.py
index d0cb1bb67..3b081ad0f 100644
--- a/dragonflow/controller/common/constants.py
+++ b/dragonflow/controller/common/constants.py
@@ -26,6 +26,8 @@
 # translated to network id and the packet is forwarded to
 # INGRESS_DESTINATION_PORT_LOOKUP_TABLE.
 INGRESS_CLASSIFICATION_DISPATCH_TABLE = 0
+# Detect reg6 (provider network and dNAT)
+EXTERNAL_INGRESS_DETECT_SOURCE_TABLE = 2
 # All packets from unknown ovs ports are dropped here. Other packets
 # are forwarded to table EGRESS_CONNTRACK_TABLE.
 EGRESS_PORT_SECURITY_TABLE = 5