IPv6 display suitable message when MTU is invalid on iface

IPv6 protocol requires a minimum MTU of 1280 bytes on the interface
to configure an IPv6 address to the interface. This patch logs an
appropriate error message and exits the agent if ipv6 is enabled and
network_device_mtu is less than the minimum value.

DocImpact

Closes-Bug: #1475015
Change-Id: I13666de4e6f5f6775ad26342e513c3c17a003b8e

neutron/agent/linux/interface.py

@@ -25,6 +25,7 @@ from neutron.agent.linux import ip_lib
 from neutron.agent.linux import utils
 from neutron.common import constants as n_const
 from neutron.common import exceptions
+from neutron.common import ipv6_utils
 from neutron.i18n import _LE, _LI
 
 
@@ -51,6 +52,17 @@ class LinuxInterfaceDriver(object):
 
     def __init__(self, conf):
         self.conf = conf
+        if self.conf.network_device_mtu:
+            self._validate_network_device_mtu()
+
+    def _validate_network_device_mtu(self):
+        if (ipv6_utils.is_enabled() and
+            self.conf.network_device_mtu < n_const.IPV6_MIN_MTU):
+            LOG.error(_LE("IPv6 protocol requires a minimum MTU of "
+                          "%(min_mtu)s, while the configured value is "
+                          "%(current_mtu)s"), {'min_mtu': n_const.IPV6_MIN_MTU,
+                          'current_mtu': self.conf.network_device_mtu})
+            raise SystemExit(1)
 
     def init_l3(self, device_name, ip_cidrs, namespace=None,
                 preserve_ips=[], gateway_ips=None,

neutron/common/constants.py

@@ -190,6 +190,7 @@ RPC_NAMESPACE_RESOURCES = None
 
 # Default network MTU value when not configured
 DEFAULT_NETWORK_MTU = 0
+IPV6_MIN_MTU = 1280
 
 ROUTER_MARK_MASK = "0xffff"
 

neutron/tests/unit/agent/common/test_utils.py

@@ -27,6 +27,7 @@ class TestLoadInterfaceDriver(base.BaseTestCase):
     def setUp(self):
         super(TestLoadInterfaceDriver, self).setUp()
         self.conf = config.setup_conf()
+        self.conf.register_opts(interface.OPTS)
         config.register_interface_driver_opts_helper(self.conf)
 
     def test_load_interface_driver_not_set(self):

neutron/tests/unit/agent/linux/test_interface.py

@@ -15,6 +15,7 @@
 
 import mock
 from oslo_utils import uuidutils
+import testtools
 
 from neutron.agent.common import config
 from neutron.agent.common import ovs_lib
@@ -335,6 +336,13 @@ class TestOVSInterfaceDriver(TestBase):
         self.conf.set_override('network_device_mtu', 9000)
         self.assertEqual(self.conf.network_device_mtu, 9000)
 
+    def test_validate_min_ipv6_mtu(self):
+        self.conf.set_override('network_device_mtu', 1200)
+        with mock.patch('neutron.common.ipv6_utils.is_enabled') as ipv6_status:
+            with testtools.ExpectedException(SystemExit):
+                ipv6_status.return_value = True
+                BaseChild(self.conf)
+
     def test_plug_mtu(self):
         self.conf.set_override('network_device_mtu', 9000)
         self._test_plug([mock.call().device().link.set_mtu(9000)])