diff --git a/neutron/db/ipam_pluggable_backend.py b/neutron/db/ipam_pluggable_backend.py
index dc26346bd60..ea118a8a582 100644
--- a/neutron/db/ipam_pluggable_backend.py
+++ b/neutron/db/ipam_pluggable_backend.py
@@ -476,12 +476,12 @@ class IpamPluggableBackend(ipam_backend_mixin.IpamBackendMixin):
                 LOG.debug("Requesting with IP request: %s port: %s ip: %s "
                           "for subnet %s and ipam_subnet %s", ip_request,
                           port, ip, subnet, ipam_subnet)
-                ip_address = ipam_subnet.allocate(ip_request)
-                allocated = models_v2.IPAllocation(network_id=network_id,
-                                                   port_id=port['id'],
-                                                   ip_address=ip_address,
-                                                   subnet_id=subnet['id'])
                 try:
+                    ip_address = ipam_subnet.allocate(ip_request)
+                    allocated = models_v2.IPAllocation(network_id=network_id,
+                                                       port_id=port['id'],
+                                                       ip_address=ip_address,
+                                                       subnet_id=subnet['id'])
                     # Do the insertion of each IP allocation entry within
                     # the context of a nested transaction, so that the entry
                     # is rolled back independently of other entries whenever
@@ -499,6 +499,10 @@ class IpamPluggableBackend(ipam_backend_mixin.IpamBackendMixin):
                     except Exception:
                         LOG.debug("Reverting IP allocation failed for %s",
                                   ip_address)
+                except ipam_exc.IpAddressAlreadyAllocated:
+                    LOG.debug("Port %s got IPv6 auto-address in a concurrent "
+                              "create or update port request. Ignoring.",
+                              port['id'])
             return updated_ports
 
     def allocate_subnet(self, context, network, subnet, subnetpool_id):
diff --git a/neutron/tests/unit/db/test_db_base_plugin_v2.py b/neutron/tests/unit/db/test_db_base_plugin_v2.py
index d9db78bb697..a55d9bdf555 100644
--- a/neutron/tests/unit/db/test_db_base_plugin_v2.py
+++ b/neutron/tests/unit/db/test_db_base_plugin_v2.py
@@ -56,6 +56,7 @@ from neutron.db.models import securitygroup as sg_models
 from neutron.db import models_v2
 from neutron.db import rbac_db_models
 from neutron.db import standard_attr
+from neutron.ipam.drivers.neutrondb_ipam import driver as ipam_driver
 from neutron.ipam import exceptions as ipam_exc
 from neutron.tests import base
 from neutron.tests import tools
@@ -4342,7 +4343,8 @@ class TestSubnetsV2(NeutronDbPluginV2TestCase):
 
     def _test_create_subnet_ipv6_auto_addr_with_port_on_network(
             self, addr_mode, device_owner=DEVICE_OWNER_COMPUTE,
-            insert_db_reference_error=False, insert_port_not_found=False):
+            insert_db_reference_error=False, insert_port_not_found=False,
+            insert_address_allocated=False):
         # Create a network with one IPv4 subnet and one port
         with self.network() as network,\
             self.subnet(network=network) as v4_subnet,\
@@ -4373,15 +4375,20 @@ class TestSubnetsV2(NeutronDbPluginV2TestCase):
                 if insert_port_not_found:
                     mock_updated_port.side_effect = lib_exc.PortNotFound(
                         port_id=port['port']['id'])
+                if insert_address_allocated:
+                    mock.patch.object(
+                        ipam_driver.NeutronDbSubnet, '_verify_ip',
+                        side_effect=ipam_exc.IpAddressAlreadyAllocated(
+                            subnet_id=mock.ANY, ip=mock.ANY)).start()
                 v6_subnet = self._make_subnet(self.fmt, network, 'fe80::1',
                                               'fe80::/64', ip_version=6,
                                               ipv6_ra_mode=addr_mode,
                                               ipv6_address_mode=addr_mode)
-            if (insert_db_reference_error
+            if (insert_db_reference_error or insert_address_allocated
                 or device_owner == constants.DEVICE_OWNER_ROUTER_SNAT
                 or device_owner in constants.ROUTER_INTERFACE_OWNERS):
-                # DVR SNAT and router interfaces should not have been
-                # updated with addresses from the new auto-address subnet
+                # DVR SNAT, router interfaces and DHCP ports should not have
+                # been updated with addresses from the new auto-address subnet
                 self.assertEqual(1, len(port['port']['fixed_ips']))
             else:
                 # Confirm that the port has been updated with an address
@@ -4411,6 +4418,14 @@ class TestSubnetsV2(NeutronDbPluginV2TestCase):
             constants.IPV6_SLAAC,
             device_owner=constants.DEVICE_OWNER_DHCP)
 
+    def test_create_subnet_dhcpv6_stateless_with_ip_already_allocated(self):
+        self._test_create_subnet_ipv6_auto_addr_with_port_on_network(
+            constants.DHCPV6_STATELESS, insert_address_allocated=True)
+
+    def test_create_subnet_ipv6_slaac_with_ip_already_allocated(self):
+        self._test_create_subnet_ipv6_auto_addr_with_port_on_network(
+            constants.IPV6_SLAAC, insert_address_allocated=True)
+
     def test_create_subnet_ipv6_slaac_with_router_intf_on_network(self):
         self._test_create_subnet_ipv6_auto_addr_with_port_on_network(
             constants.IPV6_SLAAC,