Fix: set IPv6 forwarding when there's an IPv6 gw

Currently when there is an IPv6 gateway set, IPv6 forwarding
configuration is skipped. This patch fixes it and also adds test
coverage to check the values of `accept_ra` and `forwarding` with
and without an IPv6 gateway.

Related-bug: #1667756

Change-Id: I0297aa6d0afeb56a8c69be41424d4b70509377d2

neutron/agent/l3/router_info.py

@@ -649,16 +649,19 @@ class RouterInfo(object):
         if not self.use_ipv6:
             return
 
-        if not enabled:
+        disable_ra = not enabled
+        if enabled:
+            gateway_ips = self._get_external_gw_ips(ex_gw_port)
+            if not self.is_v6_gateway_set(gateway_ips):
+                # There is no IPv6 gw_ip, use RouterAdvt for default route.
+                self.driver.configure_ipv6_ra(
+                    ns_name, interface_name, n_const.ACCEPT_RA_WITH_FORWARDING)
+            else:
+                # Otherwise, disable it
+                disable_ra = True
+        if disable_ra:
             self.driver.configure_ipv6_ra(ns_name, interface_name,
                                           n_const.ACCEPT_RA_DISABLED)
-        else:
-            gateway_ips = self._get_external_gw_ips(ex_gw_port)
-            if self.is_v6_gateway_set(gateway_ips):
-                return
-            # There is no IPv6 gw_ip, use RouterAdvt for default route.
-            self.driver.configure_ipv6_ra(ns_name, interface_name,
-                                          n_const.ACCEPT_RA_WITH_FORWARDING)
         self.driver.configure_ipv6_forwarding(ns_name, interface_name, enabled)
 
     def _external_gateway_added(self, ex_gw_port, interface_name,

neutron/tests/functional/agent/l3/test_ha_router.py

@@ -98,9 +98,9 @@ class L3HATestCase(framework.L3AgentTestFramework):
         self._router_lifecycle(enable_ha=True, dual_stack=True,
                                v6_ext_gw_with_sub=False)
 
-    @testtools.skipUnless(ipv6_utils.is_enabled_and_bind_by_default(),
-                          "IPv6 is not enabled")
-    def test_ipv6_router_advts_and_fwd_after_router_state_change_master(self):
+    def _test_ipv6_router_advts_and_fwd_helper(self, state, enable_v6_gw,
+                                               expected_ra,
+                                               expected_forwarding):
         # Schedule router to l3 agent, and then add router gateway. Verify
         # that router gw interface is configured to receive Router Advts and
         # IPv6 forwarding is enabled.
@@ -108,30 +108,44 @@ class L3HATestCase(framework.L3AgentTestFramework):
             enable_snat=True, enable_ha=True, dual_stack=True, enable_gw=False)
         router = self.manage_router(self.agent, router_info)
         common_utils.wait_until_true(lambda: router.ha_state == 'master')
+        if state == 'backup':
+            self.fail_ha_router(router)
+            common_utils.wait_until_true(lambda: router.ha_state == 'backup')
         _ext_dev_name, ex_port = l3_test_common.prepare_ext_gw_test(
-            mock.Mock(), router)
+            mock.Mock(), router, dual_stack=enable_v6_gw)
         router_info['gw_port'] = ex_port
         router.process()
-        self._assert_ipv6_accept_ra(router)
-        self._assert_ipv6_forwarding(router)
+        self._assert_ipv6_accept_ra(router, expected_ra)
+        self._assert_ipv6_forwarding(router, expected_forwarding)
+
+    @testtools.skipUnless(ipv6_utils.is_enabled_and_bind_by_default(),
+                          "IPv6 is not enabled")
+    def test_ipv6_router_advts_and_fwd_after_router_state_change_master(self):
+        # Check that RA and forwarding are enabled when there's no IPv6
+        # gateway.
+        self._test_ipv6_router_advts_and_fwd_helper('master',
+                                                    enable_v6_gw=False,
+                                                    expected_ra=True,
+                                                    expected_forwarding=True)
+        # Check that RA is disabled and forwarding is enabled when an IPv6
+        # gateway is configured.
+        self._test_ipv6_router_advts_and_fwd_helper('master',
+                                                    enable_v6_gw=True,
+                                                    expected_ra=False,
+                                                    expected_forwarding=True)
 
     @testtools.skipUnless(ipv6_utils.is_enabled_and_bind_by_default(),
                           "IPv6 is not enabled")
     def test_ipv6_router_advts_and_fwd_after_router_state_change_backup(self):
-        # Schedule router to l3 agent, and then add router gateway. Verify
-        # that router gw interface is configured to discard Router Advts and
-        # IPv6 forwarding is disabled.
-        router_info = l3_test_common.prepare_router_data(
-            enable_snat=True, enable_ha=True, dual_stack=True, enable_gw=False)
-        router = self.manage_router(self.agent, router_info)
-        self.fail_ha_router(router)
-        common_utils.wait_until_true(lambda: router.ha_state == 'backup')
-        _ext_dev_name, ex_port = l3_test_common.prepare_ext_gw_test(
-            mock.Mock(), router)
-        router_info['gw_port'] = ex_port
-        router.process()
-        self._assert_ipv6_accept_ra(router, False)
-        self._assert_ipv6_forwarding(router, False)
+        # Check that both RA and forwarding are disabled on backup instances
+        self._test_ipv6_router_advts_and_fwd_helper('backup',
+                                                    enable_v6_gw=False,
+                                                    expected_ra=False,
+                                                    expected_forwarding=False)
+        self._test_ipv6_router_advts_and_fwd_helper('backup',
+                                                    enable_v6_gw=True,
+                                                    expected_ra=False,
+                                                    expected_forwarding=False)
 
     def test_keepalived_configuration(self):
         router_info = self.generate_router_info(enable_ha=True)