Make agent interface plugging utilize network MTU

This changes the 'plug' and 'plug_new' interfaces of the
LinuxInterfaceDriver to accept an MTU argument. It then
updates the dhcp agent and l3 agent to pass the MTU that
is set on the network that the port belongs to. This allows
it to take into account the overhead calculations that are
done for encapsulation types.

It's necessary for the L3 agent to have the MTU because it
must recognize when fragmentation is needed so it can fragment
or generate an ICMP error.

It's necessary for the DHCP agent to have the MTU so it doesn't
interfere when it plugs into a bridge with a larger than 1500
MTU (the bridge would reduce its MTU to match the agent).

If an operator sets 'network_device_mtu', the value of that
will be used instead to preserve previous behavior.

Closes-Bug: #1549470
Closes-Bug: #1542108
Closes-Bug: #1542475
DocImpact: Neutron agents now support arbitrary MTU
           configurations on each network (including
           jumbo frames). This is accomplished by checking
           the MTU value defined for each network on which
           it is wiring VIFs.
Co-Authored-By: Matt Kassawara <mkassawara@gmail.com>
Change-Id: Ic091fa78dfd133179c71cbc847bf955a06cb248a

neutron/agent/l3/dvr_edge_ha_router.py

@@ -117,4 +117,5 @@ class DvrEdgeHaRouter(DvrEdgeRouter, HaRouter):
         self.driver.plug(port['network_id'], port['id'],
                          interface_name, port['mac_address'],
                          namespace=self.snat_namespace.name,
-                         prefix=dvr_snat_ns.SNAT_INT_DEV_PREFIX)
+                         prefix=dvr_snat_ns.SNAT_INT_DEV_PREFIX,
+                         mtu=port.get('mtu'))

neutron/agent/l3/dvr_edge_router.py

@@ -104,7 +104,8 @@ class DvrEdgeRouter(dvr_local_router.DvrLocalRouter):
             sn_port['fixed_ips'],
             sn_port['mac_address'],
             interface_name,
-            dvr_snat_ns.SNAT_INT_DEV_PREFIX)
+            dvr_snat_ns.SNAT_INT_DEV_PREFIX,
+            mtu=sn_port.get('mtu'))
 
     def _dvr_internal_network_removed(self, port):
         super(DvrEdgeRouter, self)._dvr_internal_network_removed(port)
@@ -132,7 +133,8 @@ class DvrEdgeRouter(dvr_local_router.DvrLocalRouter):
             self.snat_namespace.name, port['network_id'],
             port['id'], port['fixed_ips'],
             port['mac_address'], interface_name,
-            dvr_snat_ns.SNAT_INT_DEV_PREFIX)
+            dvr_snat_ns.SNAT_INT_DEV_PREFIX,
+            mtu=port.get('mtu'))
 
     def _create_dvr_gateway(self, ex_gw_port, gw_interface_name):
         """Create SNAT namespace."""

neutron/agent/l3/dvr_fip_ns.py

@@ -106,7 +106,8 @@ class FipNamespace(namespaces.Namespace):
                          ex_gw_port['mac_address'],
                          bridge=self.agent_conf.external_network_bridge,
                          namespace=ns_name,
-                         prefix=FIP_EXT_DEV_PREFIX)
+                         prefix=FIP_EXT_DEV_PREFIX,
+                         mtu=ex_gw_port.get('mtu'))
 
         ip_cidrs = common_utils.fixed_ip_cidrs(ex_gw_port['fixed_ips'])
         self.driver.init_l3(interface_name, ip_cidrs, namespace=ns_name,
@@ -232,9 +233,11 @@ class FipNamespace(namespaces.Namespace):
             self._internal_ns_interface_added(str(fip_2_rtr),
                                               fip_2_rtr_name,
                                               fip_ns_name)
-            if self.agent_conf.network_device_mtu:
+            mtu = (self.agent_conf.network_device_mtu or
-                int_dev[0].link.set_mtu(self.agent_conf.network_device_mtu)
+                   ri.get_ex_gw_port().get('mtu'))
-                int_dev[1].link.set_mtu(self.agent_conf.network_device_mtu)
+            if mtu:
+                int_dev[0].link.set_mtu(mtu)
+                int_dev[1].link.set_mtu(mtu)
             int_dev[0].link.set_up()
             int_dev[1].link.set_up()
 

neutron/agent/l3/ha_router.py

@@ -144,7 +144,8 @@ class HaRouter(router.RouterInfo):
                          interface_name,
                          self.ha_port['mac_address'],
                          namespace=self.ha_namespace,
-                         prefix=HA_DEV_PREFIX)
+                         prefix=HA_DEV_PREFIX,
+                         mtu=self.ha_port.get('mtu'))
         ip_cidrs = common_utils.fixed_ip_cidrs(self.ha_port['fixed_ips'])
         self.driver.init_l3(interface_name, ip_cidrs,
                             namespace=self.ha_namespace,
@@ -268,13 +269,13 @@ class HaRouter(router.RouterInfo):
     def _plug_ha_router_port(self, port, name_getter, prefix):
         port_id = port['id']
         interface_name = name_getter(port_id)
-
         self.driver.plug(port['network_id'],
                          port_id,
                          interface_name,
                          port['mac_address'],
                          namespace=self.ha_namespace,
-                         prefix=prefix)
+                         prefix=prefix,
+                         mtu=port.get('mtu'))
 
         self._disable_ipv6_addressing_on_interface(interface_name)
         self._add_vips(port, interface_name)

neutron/agent/l3/router_info.py

@@ -361,12 +361,12 @@ class RouterInfo(object):
 
     def _internal_network_added(self, ns_name, network_id, port_id,
                                 fixed_ips, mac_address,
-                                interface_name, prefix):
+                                interface_name, prefix, mtu=None):
         LOG.debug("adding internal network: prefix(%s), port(%s)",
                   prefix, port_id)
         self.driver.plug(network_id, port_id, interface_name, mac_address,
                          namespace=ns_name,
-                         prefix=prefix)
+                         prefix=prefix, mtu=mtu)
 
         ip_cidrs = common_utils.fixed_ip_cidrs(fixed_ips)
         self.driver.init_router_port(
@@ -391,7 +391,8 @@ class RouterInfo(object):
                                      fixed_ips,
                                      mac_address,
                                      interface_name,
-                                     INTERNAL_DEV_PREFIX)
+                                     INTERNAL_DEV_PREFIX,
+                                     mtu=port.get('mtu'))
 
     def internal_network_removed(self, port):
         interface_name = self.get_internal_device_name(port['id'])
@@ -557,7 +558,8 @@ class RouterInfo(object):
                          ex_gw_port['mac_address'],
                          bridge=self.agent_conf.external_network_bridge,
                          namespace=ns_name,
-                         prefix=EXTERNAL_DEV_PREFIX)
+                         prefix=EXTERNAL_DEV_PREFIX,
+                         mtu=ex_gw_port.get('mtu'))
 
     def _get_external_gw_ips(self, ex_gw_port):
         gateway_ips = []

neutron/agent/linux/dhcp.py

@@ -1230,7 +1230,8 @@ class DeviceManager(object):
                                  port.id,
                                  interface_name,
                                  port.mac_address,
-                                 namespace=network.namespace)
+                                 namespace=network.namespace,
+                                 mtu=network.get('mtu'))
             except Exception:
                 with excutils.save_and_reraise_exception():
                     LOG.exception(_LE('Unable to plug DHCP port for '

neutron/agent/linux/interface.py

@@ -20,7 +20,7 @@ from oslo_config import cfg
 from oslo_log import log as logging
 import six
 
-from neutron._i18n import _, _LE, _LI
+from neutron._i18n import _, _LE, _LI, _LW
 from neutron.agent.common import ovs_lib
 from neutron.agent.linux import ip_lib
 from neutron.agent.linux import utils
@@ -233,15 +233,15 @@ class LinuxInterfaceDriver(object):
 
     @abc.abstractmethod
     def plug_new(self, network_id, port_id, device_name, mac_address,
-                 bridge=None, namespace=None, prefix=None):
+                 bridge=None, namespace=None, prefix=None, mtu=None):
         """Plug in the interface only for new devices that don't exist yet."""
 
     def plug(self, network_id, port_id, device_name, mac_address,
-             bridge=None, namespace=None, prefix=None):
+             bridge=None, namespace=None, prefix=None, mtu=None):
         if not ip_lib.device_exists(device_name,
                                     namespace=namespace):
             self.plug_new(network_id, port_id, device_name, mac_address,
-                          bridge, namespace, prefix)
+                          bridge, namespace, prefix, mtu)
         else:
             LOG.info(_LI("Device %s already exists"), device_name)
 
@@ -269,7 +269,7 @@ class LinuxInterfaceDriver(object):
 
 class NullDriver(LinuxInterfaceDriver):
     def plug_new(self, network_id, port_id, device_name, mac_address,
-                 bridge=None, namespace=None, prefix=None):
+                 bridge=None, namespace=None, prefix=None, mtu=None):
         pass
 
     def unplug(self, device_name, bridge=None, namespace=None, prefix=None):
@@ -304,7 +304,7 @@ class OVSInterfaceDriver(LinuxInterfaceDriver):
         ovs.replace_port(device_name, *attrs)
 
     def plug_new(self, network_id, port_id, device_name, mac_address,
-                 bridge=None, namespace=None, prefix=None):
+                 bridge=None, namespace=None, prefix=None, mtu=None):
         """Plug in the interface."""
         if not bridge:
             bridge = self.conf.ovs_integration_bridge
@@ -328,11 +328,13 @@ class OVSInterfaceDriver(LinuxInterfaceDriver):
 
         ns_dev.link.set_address(mac_address)
 
-        if self.conf.network_device_mtu:
+        mtu = self.conf.network_device_mtu or mtu
-            ns_dev.link.set_mtu(self.conf.network_device_mtu)
+        if mtu:
+            ns_dev.link.set_mtu(mtu)
             if self.conf.ovs_use_veth:
-                root_dev.link.set_mtu(self.conf.network_device_mtu)
+                root_dev.link.set_mtu(mtu)
-
+        else:
+            LOG.warning(_LW("No MTU configured for port %s"), port_id)
         # Add an interface created by ovs to the namespace.
         if not self.conf.ovs_use_veth and namespace:
             namespace_obj = ip.ensure_namespace(namespace)
@@ -381,7 +383,7 @@ class IVSInterfaceDriver(LinuxInterfaceDriver):
         utils.execute(cmd, run_as_root=True)
 
     def plug_new(self, network_id, port_id, device_name, mac_address,
-                 bridge=None, namespace=None, prefix=None):
+                 bridge=None, namespace=None, prefix=None, mtu=None):
         """Plug in the interface."""
         ip = ip_lib.IPWrapper()
         tap_name = self._get_tap_name(device_name, prefix)
@@ -393,9 +395,12 @@ class IVSInterfaceDriver(LinuxInterfaceDriver):
         ns_dev = ip.device(device_name)
         ns_dev.link.set_address(mac_address)
 
-        if self.conf.network_device_mtu:
+        mtu = self.conf.network_device_mtu or mtu
-            ns_dev.link.set_mtu(self.conf.network_device_mtu)
+        if mtu:
-            root_dev.link.set_mtu(self.conf.network_device_mtu)
+            ns_dev.link.set_mtu(mtu)
+            root_dev.link.set_mtu(mtu)
+        else:
+            LOG.warning(_LW("No MTU configured for port %s"), port_id)
 
         if namespace:
             namespace_obj = ip.ensure_namespace(namespace)
@@ -424,7 +429,7 @@ class BridgeInterfaceDriver(LinuxInterfaceDriver):
     DEV_NAME_PREFIX = 'ns-'
 
     def plug_new(self, network_id, port_id, device_name, mac_address,
-                 bridge=None, namespace=None, prefix=None):
+                 bridge=None, namespace=None, prefix=None, mtu=None):
         """Plugin the interface."""
         ip = ip_lib.IPWrapper()
 
@@ -436,9 +441,12 @@ class BridgeInterfaceDriver(LinuxInterfaceDriver):
                                          namespace2=namespace)
         ns_veth.link.set_address(mac_address)
 
-        if self.conf.network_device_mtu:
+        mtu = self.conf.network_device_mtu or mtu
-            root_veth.link.set_mtu(self.conf.network_device_mtu)
+        if mtu:
-            ns_veth.link.set_mtu(self.conf.network_device_mtu)
+            root_veth.link.set_mtu(mtu)
+            ns_veth.link.set_mtu(mtu)
+        else:
+            LOG.warning(_LW("No MTU configured for port %s"), port_id)
 
         root_veth.link.set_up()
         ns_veth.link.set_up()

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

@@ -51,6 +51,10 @@ class TestDvrRouter(framework.L3AgentTestFramework):
         self.agent.conf.agent_mode = 'dvr'
         self._test_update_floatingip_statuses(self.generate_dvr_router_info())
 
+    def test_dvr_router_lifecycle_ha_with_snat_with_fips_nmtu(self):
+        self._dvr_router_lifecycle(enable_ha=True, enable_snat=True,
+                                   use_port_mtu=True)
+
     def test_dvr_router_lifecycle_without_ha_without_snat_with_fips(self):
         self._dvr_router_lifecycle(enable_ha=False, enable_snat=False)
 
@@ -101,7 +105,7 @@ class TestDvrRouter(framework.L3AgentTestFramework):
         self._validate_fips_for_external_network(router2, fip2_ns)
 
     def _dvr_router_lifecycle(self, enable_ha=False, enable_snat=False,
-                              custom_mtu=2000,
+                              custom_mtu=2000, use_port_mtu=False,
                               ip_version=4,
                               dual_stack=False):
         '''Test dvr router lifecycle
@@ -115,11 +119,19 @@ class TestDvrRouter(framework.L3AgentTestFramework):
         # Since by definition this is a dvr (distributed = true)
         # only dvr and dvr_snat are applicable
         self.agent.conf.agent_mode = 'dvr_snat' if enable_snat else 'dvr'
-        self.agent.conf.network_device_mtu = custom_mtu
 
         # We get the router info particular to a dvr router
         router_info = self.generate_dvr_router_info(
             enable_ha, enable_snat, extra_routes=True)
+        if use_port_mtu:
+            for key in ('_interfaces', '_snat_router_interfaces',
+                        '_floatingip_agent_interfaces'):
+                for port in router_info[key]:
+                    port['mtu'] = custom_mtu
+            router_info['gw_port']['mtu'] = custom_mtu
+            router_info['_ha_interface']['mtu'] = custom_mtu
+        else:
+            self.agent.conf.network_device_mtu = custom_mtu
 
         # We need to mock the get_agent_gateway_port return value
         # because the whole L3PluginApi is mocked and we need the port
@@ -156,6 +168,9 @@ class TestDvrRouter(framework.L3AgentTestFramework):
                 router.get_internal_device_name,
                 router.ns_name)
             utils.wait_until_true(device_exists)
+            name = router.get_internal_device_name(device['id'])
+            self.assertEqual(custom_mtu,
+                             ip_lib.IPDevice(name, router.ns_name).link.mtu)
 
         ext_gateway_port = router_info['gw_port']
         self.assertTrue(self._namespace_exists(router.ns_name))

neutron/tests/functional/agent/test_dhcp_agent.py

@@ -253,6 +253,15 @@ class DHCPAgentOVSTestCase(DHCPAgentOVSTestFramework):
                                             dhcp_enabled=dhcp_enabled)
             self.assert_dhcp_resources(network, dhcp_enabled)
 
+    def test_agent_mtu_set_on_interface_driver(self):
+        network = self.network_dict_for_dhcp()
+        network["mtu"] = 789
+        self.configure_dhcp_for_network(network=network)
+        port = network.ports[0]
+        iface_name = self.get_interface_name(network, port)
+        dev = ip_lib.IPDevice(iface_name, network.namespace)
+        self.assertEqual(789, dev.link.mtu)
+
     def test_good_address_allocation(self):
         network, port = self._get_network_port_for_allocation_test()
         network.ports.append(port)

neutron/tests/unit/agent/dhcp/test_agent.py

@@ -1309,7 +1309,8 @@ class TestDeviceManager(base.BaseTestCase):
                                            port.id,
                                            'tap12345678-12',
                                            'aa:bb:cc:dd:ee:ff',
-                                           namespace=net.namespace))
+                                           namespace=net.namespace,
+                                           mtu=None))
         self.mock_driver.assert_has_calls(expected)
 
         dh._set_default_route.assert_called_once_with(net, 'tap12345678-12')

neutron/tests/unit/agent/l3/test_agent.py

@@ -390,7 +390,8 @@ class TestBasicRouterOperations(BasicRouterOperationsFramework):
                 sn_port['fixed_ips'],
                 sn_port['mac_address'],
                 ri._get_snat_int_device_name(sn_port['id']),
-                dvr_snat_ns.SNAT_INT_DEV_PREFIX)
+                dvr_snat_ns.SNAT_INT_DEV_PREFIX,
+                mtu=None)
         elif action == 'remove':
             self.device_exists.return_value = False
             ri.get_snat_port_for_internal_port = mock.Mock(

releasenotes/notes/end-to-end-mtu-00345fc4282cb8fb.yaml

@@ -0,0 +1,20 @@
+---
+features:
+  - Use the value of the network 'mtu' attribute for the MTU
+    of virtual network interfaces such as veth pairs, patch
+    ports, and tap devices involving a particular network.
+  - Enable end-to-end support for arbitrary MTUs including
+    jumbo frames between instances and provider networks by
+    moving MTU disparities between flat or VLAN networks and
+    overlay networks from layer-2 devices to layer-3 devices
+    that support path MTU discovery (PMTUD).
+upgrade:
+  - Does not change MTU for existing virtual network interfaces.
+  - Actions that create virtual network interfaces on an existing
+    network with the 'mtu' attribute containing a value greater
+    than zero could cause issues for network traffic traversing
+    existing and new virtual network interfaces.
+fixes:
+  - Explicitly configure MTU of virtual network interfaces
+    rather than using default values or incorrect values that
+    do not account for overlay protocol overhead.