diff --git a/vmware_nsx/plugins/nsx_v/drivers/distributed_router_driver.py b/vmware_nsx/plugins/nsx_v/drivers/distributed_router_driver.py
index 779de5461e..3a9c2c92b5 100644
--- a/vmware_nsx/plugins/nsx_v/drivers/distributed_router_driver.py
+++ b/vmware_nsx/plugins/nsx_v/drivers/distributed_router_driver.py
@@ -12,6 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import netaddr
 from oslo_log import log as logging
 from oslo_utils import excutils
 
@@ -208,8 +209,9 @@ class RouterDistributedDriver(router_driver.RouterBaseDriver):
         if new_ext_net_id:
             self._notify_after_router_edge_association(context, router)
 
-    def _validate_multiple_subnets_routers(self, context, router_id,
-                                           interface_info):
+    def _validate_subnets_routers(self, context, router_id,
+                                  interface_info):
+        # Validate that multiple subnets are not connected to the router
         _nsxv_plugin = self.plugin
         net_id, subnet_id = _nsxv_plugin._get_interface_info(context,
                                                              interface_info)
@@ -233,10 +235,16 @@ class RouterDistributedDriver(router_driver.RouterBaseDriver):
             else:
                 # attach to multiple routers
                 raise n_exc.Conflict(error_message=err_msg)
+        # Validate that the subnet is not a v6 one
+        subnet = self.plugin.get_subnet(context.elevated(), subnet_id)
+        if (subnet.get('ip_version') == 6 or
+            (subnet['cidr'] not in (constants.ATTR_NOT_SPECIFIED, None)
+             and netaddr.IPNetwork(subnet['cidr']).version == 6)):
+            err_msg = _("No support for IPv6 interfaces")
+            raise n_exc.InvalidInput(error_message=err_msg)
 
     def add_router_interface(self, context, router_id, interface_info):
-        self._validate_multiple_subnets_routers(
-            context, router_id, interface_info)
+        self._validate_subnets_routers(context, router_id, interface_info)
         info = super(nsx_v.NsxVPluginV2, self.plugin).add_router_interface(
             context, router_id, interface_info)
 
diff --git a/vmware_nsx/tests/unit/nsx_v/test_plugin.py b/vmware_nsx/tests/unit/nsx_v/test_plugin.py
index 6f4a0397f4..0b6bac2504 100644
--- a/vmware_nsx/tests/unit/nsx_v/test_plugin.py
+++ b/vmware_nsx/tests/unit/nsx_v/test_plugin.py
@@ -4324,6 +4324,31 @@ class TestVdrTestCase(L3NatTest, L3NatTestCaseBase,
                       self).test_update_subnet_gateway_for_external_net()
                 self.assertTrue(update_nexthop.called)
 
+    def test_router_add_interface_ipv6_port_existing_network_returns_400(self):
+        """Ensure unique IPv6 router ports per network id.
+        Adding a router port containing one or more IPv6 subnets with the same
+        network id as an existing router port should fail. This is so
+        there is no ambiguity regarding on which port to add an IPv6 subnet
+        when executing router-interface-add with a subnet and no port.
+        """
+        with self.network() as n, self.router() as r:
+            with self.subnet(network=n, cidr='fd00::/64',
+                             ip_version=6, enable_dhcp=False) as s1, (
+                 self.subnet(network=n, cidr='fd01::/64',
+                             ip_version=6, enable_dhcp=False)) as s2:
+                with self.port(subnet=s1) as p:
+                    exp_code = webob.exc.HTTPBadRequest.code
+                    self._router_interface_action('add',
+                                                  r['router']['id'],
+                                                  s2['subnet']['id'],
+                                                  None,
+                                                  expected_code=exp_code)
+                    self._router_interface_action('add',
+                                                  r['router']['id'],
+                                                  None,
+                                                  p['port']['id'],
+                                                  expected_code=exp_code)
+
 
 class TestNSXvAllowedAddressPairs(NsxVPluginV2TestCase,
                                   test_addr_pair.TestAllowedAddressPairs):