diff -Nru neutron-16.3.1/debian/changelog neutron-16.3.1/debian/changelog
--- neutron-16.3.1/debian/changelog	2021-04-12 17:43:59.000000000 +0530
+++ neutron-16.3.1/debian/changelog	2021-04-27 08:43:12.000000000 +0530
@@ -1,3 +1,10 @@
+neutron (2:16.3.1-0ubuntu2) focal; urgency=medium
+
+  * Fix to check L3 agent gateway port robustly (LP: #1883089)
+    - d/p/0001-L3-Check-agent-gateway-port-robustly.patch 
+
+ -- Hemanth Nakkina <hemanth.nakkina@canonical.com>  Tue, 27 Apr 2021 08:43:12 +0530
+
 neutron (2:16.3.1-0ubuntu1) focal; urgency=medium
 
   * New stable point release for OpenStack Ussuri (LP: #1923036).
diff -Nru neutron-16.3.1/debian/patches/0001-L3-Check-agent-gateway-port-robustly.patch neutron-16.3.1/debian/patches/0001-L3-Check-agent-gateway-port-robustly.patch
--- neutron-16.3.1/debian/patches/0001-L3-Check-agent-gateway-port-robustly.patch	1970-01-01 05:30:00.000000000 +0530
+++ neutron-16.3.1/debian/patches/0001-L3-Check-agent-gateway-port-robustly.patch	2021-04-27 08:42:14.000000000 +0530
@@ -0,0 +1,92 @@
+From 4093727ae9c751cce8c39dd0eb022b2c9b90d624 Mon Sep 17 00:00:00 2001
+From: LIU Yulong <i@liuyulong.me>
+Date: Sat, 13 Jun 2020 23:14:47 +0800
+Subject: [PATCH] [L3] Check agent gateway port robustly
+
+In patch [1] it introduced a binding of DB uniq constraint for L3
+agent gateway. In some extreme case the DvrFipGatewayPortAgentBinding
+is in DB while the gateway port not. The current code path only checks
+the binding existence which will pass a "None" port to the following
+code path that results an AttributeError. This patch adds a simple check
+for that gateway port, if it is not created, new one.
+
+[1] https://review.opendev.org/#/c/702547/
+
+Closes-Bug: #1883089
+Change-Id: Ia90f2ee435b0a3476dbea028d3200cefe11e35e4
+(cherry picked from commit 5fdfd4cbfc56425c56b4a5702d92a97da56ab6e8)
+---
+ neutron/db/l3_dvr_db.py                 |  3 ++-
+ neutron/tests/unit/db/test_l3_dvr_db.py | 36 +++++++++++++++++++++++++
+ 2 files changed, 38 insertions(+), 1 deletion(-)
+
+diff --git a/neutron/db/l3_dvr_db.py b/neutron/db/l3_dvr_db.py
+index 463174c981..8ff05eb9d5 100644
+--- a/neutron/db/l3_dvr_db.py
++++ b/neutron/db/l3_dvr_db.py
+@@ -1096,13 +1096,14 @@ class _DVRAgentInterfaceMixin(object):
+             try:
+                 fip_agent_port_obj.create()
+             except o_exc.NeutronDbObjectDuplicateEntry:
+-                LOG.debug("Floating IP Agent Gateway port for network "
++                LOG.debug("Floating IP Gateway port agent binding for network "
+                           "%(network)s already exists on host %(host)s. "
+                           "Probably it was just created by other worker.",
+                           {'network': network_id,
+                            'host': host})
+                 agent_port = self._get_agent_gw_ports_exist_for_network(
+                     context, network_id, host, l3_agent_db['id'])
++            if agent_port:
+                 LOG.debug("Floating IP Agent Gateway port %(gw)s found "
+                           "for the destination host: %(dest_host)s",
+                           {'gw': agent_port,
+diff --git a/neutron/tests/unit/db/test_l3_dvr_db.py b/neutron/tests/unit/db/test_l3_dvr_db.py
+index e2eda73a2e..c6d08afd79 100644
+--- a/neutron/tests/unit/db/test_l3_dvr_db.py
++++ b/neutron/tests/unit/db/test_l3_dvr_db.py
+@@ -762,6 +762,42 @@ class L3DvrTestCase(test_db_base_plugin_v2.NeutronDbPluginV2TestCase):
+             mock.call(self.ctx, network_id, 'host', fipagent['id'])])
+         self.assertIsNotNone(fport)
+ 
++    def test_create_fip_agent_gw_port_agent_binding_exists(self):
++        network_id = _uuid()
++        fport_db = {'id': _uuid()}
++        self.mixin._get_agent_gw_ports_exist_for_network = mock.Mock(
++            side_effect=[None, None])
++        fipagent = agent_obj.Agent(
++                self.ctx,
++                id=_uuid(),
++                binary='foo-agent',
++                host='host',
++                agent_type='L3 agent',
++                topic='foo_topic',
++                configurations={"agent_mode": "dvr"})
++        self.mixin._get_agent_by_type_and_host = mock.Mock(
++            return_value=fipagent)
++        self.mixin._populate_mtu_and_subnets_for_ports = mock.Mock()
++
++        with mock.patch.object(
++            router_obj.DvrFipGatewayPortAgentBinding, 'create',
++            side_effect=o_exc.NeutronDbObjectDuplicateEntry(
++                mock.Mock(), mock.Mock())
++        ) as dvr_fip_gateway_port_agent_binding_create,\
++            mock.patch.object(
++                plugin_utils, "create_port", return_value=fport_db):
++            fport = self.mixin.create_fip_agent_gw_port_if_not_exists(
++                                                    self.ctx,
++                                                    network_id,
++                                                    'host')
++        dvr_fip_gateway_port_agent_binding_create.assert_called_once_with()
++        self.mixin._get_agent_gw_ports_exist_for_network.assert_has_calls([
++            mock.call(self.ctx, network_id, 'host', fipagent['id']),
++            mock.call(self.ctx, network_id, 'host', fipagent['id'])])
++        self.mixin._populate_mtu_and_subnets_for_ports.assert_has_calls([
++            mock.call(self.ctx, [fport_db])])
++        self.assertIsNotNone(fport)
++
+     def test_create_floatingip_agent_gw_port_with_non_dvr_router(self):
+         floatingip = {
+             'id': _uuid(),
+-- 
+2.25.1
+
diff -Nru neutron-16.3.1/debian/patches/series neutron-16.3.1/debian/patches/series
--- neutron-16.3.1/debian/patches/series	2021-04-12 17:43:59.000000000 +0530
+++ neutron-16.3.1/debian/patches/series	2021-04-27 08:42:14.000000000 +0530
@@ -1,2 +1,3 @@
 skip-iptest.patch
 flake8-legacy.patch
+0001-L3-Check-agent-gateway-port-robustly.patch