diff --git a/neutron/agent/linux/pd.py b/neutron/agent/linux/pd.py
index e8b9ebfa419..74cce2d4fe0 100644
--- a/neutron/agent/linux/pd.py
+++ b/neutron/agent/linux/pd.py
@@ -27,6 +27,7 @@ from oslo_utils import netutils
 import six
 from stevedore import driver
 
+from neutron.agent.linux import ip_lib
 from neutron.common import utils
 
 LOG = logging.getLogger(__name__)
@@ -209,16 +210,20 @@ class PrefixDelegation(object):
 
     def _add_lla(self, router, lla_with_mask):
         if router['gw_interface']:
-            self.intf_driver.add_ipv6_addr(router['gw_interface'],
-                                           lla_with_mask,
-                                           router['ns_name'],
-                                           'link')
-            # There is a delay before the LLA becomes active.
-            # This is because the kernel runs DAD to make sure LLA uniqueness
-            # Spawn a thread to wait for the interface to be ready
-            self._spawn_lla_thread(router['gw_interface'],
-                                   router['ns_name'],
-                                   lla_with_mask)
+            try:
+                self.intf_driver.add_ipv6_addr(router['gw_interface'],
+                                               lla_with_mask,
+                                               router['ns_name'],
+                                               'link')
+                # There is a delay before the LLA becomes active.
+                # This is because the kernel runs DAD to make sure LLA
+                # uniqueness
+                # Spawn a thread to wait for the interface to be ready
+                self._spawn_lla_thread(router['gw_interface'],
+                                       router['ns_name'],
+                                       lla_with_mask)
+            except ip_lib.IpAddressAlreadyExists:
+                pass
 
     def _spawn_lla_thread(self, gw_ifname, ns_name, lla_with_mask):
         eventlet.spawn_n(self._ensure_lla_task,
diff --git a/neutron/tests/unit/agent/l3/test_agent.py b/neutron/tests/unit/agent/l3/test_agent.py
index fa7a347976c..a0e873eb3e3 100644
--- a/neutron/tests/unit/agent/l3/test_agent.py
+++ b/neutron/tests/unit/agent/l3/test_agent.py
@@ -3814,6 +3814,53 @@ class TestBasicRouterOperations(BasicRouterOperationsFramework):
         self._pd_assert_dibbler_calls(expected_calls,
             self.external_process.mock_calls[-len(expected_calls):])
 
+    @mock.patch.object(pd.PrefixDelegation, 'update_subnet')
+    @mock.patch.object(dibbler.PDDibbler, 'get_prefix', autospec=True)
+    @mock.patch.object(dibbler.os, 'getpid', return_value=1234)
+    @mock.patch.object(pd.PrefixDelegation, '_is_lla_active',
+                       return_value=True)
+    @mock.patch.object(dibbler.os, 'chmod')
+    @mock.patch.object(dibbler.shutil, 'rmtree')
+    @mock.patch.object(pd.PrefixDelegation, '_get_sync_data')
+    def test_pd_lla_already_exists(self, mock1, mock2, mock3, mock4,
+                                   mock_getpid, mock_get_prefix,
+                                   mock_pd_update_subnet):
+        '''Test HA in the active router
+        The intent is to test the PD code with HA. To avoid unnecessary
+        complexities, use the regular router.
+        '''
+        # Initial setup
+        agent, router, ri = self._pd_setup_agent_router(enable_ha=True)
+
+        agent.pd.intf_driver = mock.MagicMock()
+        agent.pd.intf_driver.add_ipv6_addr.side_effect = (
+                ip_lib.IpAddressAlreadyExists())
+
+        # Create one pd-enabled subnet and add router interface
+        l3_test_common.router_append_pd_enabled_subnet(router)
+        self._pd_add_gw_interface(agent, ri)
+        ri.process()
+
+        # No client should be started since it's standby router
+        agent.pd.process_prefix_update()
+        self.assertFalse(self.external_process.called)
+        self.assertFalse(mock_get_prefix.called)
+
+        update_router = copy.deepcopy(router)
+        pd_intfs = l3_test_common.get_unassigned_pd_interfaces(update_router)
+
+        # Turn the router to be active
+        agent.pd.process_ha_state(router['id'], True)
+
+        # Get prefixes
+        self._pd_get_prefixes(agent, ri, [], pd_intfs, mock_get_prefix)
+
+        # Update the router with the new prefix
+        ri.router = update_router
+        ri.process()
+
+        self._pd_verify_update_results(ri, pd_intfs, mock_pd_update_subnet)
+
     @mock.patch.object(dibbler.os, 'chmod')
     def test_pd_generate_dibbler_conf(self, mock_chmod):
         pddib = dibbler.PDDibbler("router_id", "subnet-id", "ifname")