diff --git a/neutron/agent/linux/dhcp.py b/neutron/agent/linux/dhcp.py
index a6b8a87456c..38b34747b78 100644
--- a/neutron/agent/linux/dhcp.py
+++ b/neutron/agent/linux/dhcp.py
@@ -1414,6 +1414,11 @@ class DeviceManager(object):
         if ip_lib.ensure_device_is_ready(interface_name,
                                          namespace=network.namespace):
             LOG.debug('Reusing existing device: %s.', interface_name)
+            # force mtu on the port for in case it was changed for the network
+            mtu = getattr(network, 'mtu', 0)
+            if mtu:
+                self.driver.set_mtu(interface_name, mtu,
+                                    namespace=network.namespace)
         else:
             try:
                 self.plug(network, port, interface_name)
diff --git a/neutron/tests/fullstack/cmd/dhcp_agent.py b/neutron/tests/fullstack/cmd/dhcp_agent.py
index 416cd7874f1..c8f9c5150d5 100755
--- a/neutron/tests/fullstack/cmd/dhcp_agent.py
+++ b/neutron/tests/fullstack/cmd/dhcp_agent.py
@@ -30,11 +30,14 @@ OPTS = [
 ]
 
 
+def _get_namespace_name(id_, suffix=None):
+    suffix = suffix or cfg.CONF.test_namespace_suffix
+    return "%s%s%s" % (linux_dhcp.NS_PREFIX, id_, suffix)
+
+
 def NetModel_init(self, d):
     super(linux_dhcp.NetModel, self).__init__(d)
-
-    self._ns_name = "%s%s%s" % (
-        linux_dhcp.NS_PREFIX, self.id, cfg.CONF.test_namespace_suffix)
+    self._ns_name = _get_namespace_name(self.id)
 
 
 @classmethod
diff --git a/neutron/tests/fullstack/test_dhcp_agent.py b/neutron/tests/fullstack/test_dhcp_agent.py
index f5546e8a2dd..3729d340e22 100644
--- a/neutron/tests/fullstack/test_dhcp_agent.py
+++ b/neutron/tests/fullstack/test_dhcp_agent.py
@@ -17,8 +17,10 @@ import random
 from neutron_lib import constants
 from oslo_utils import uuidutils
 
+from neutron.agent.linux import ip_lib
 from neutron.common import utils as common_utils
 from neutron.tests.fullstack import base
+from neutron.tests.fullstack.cmd import dhcp_agent as cmd
 from neutron.tests.fullstack.resources import environment
 from neutron.tests.fullstack.resources import machine
 from neutron.tests.unit import testlib_api
@@ -99,6 +101,25 @@ class TestDhcpAgentNoHA(BaseDhcpAgentTest):
         # And check if IP and gateway config is fine on FakeMachine
         self.vm.block_until_dhcp_config_done()
 
+    def test_mtu_update(self):
+        self.vm.block_until_dhcp_config_done()
+
+        namespace = cmd._get_namespace_name(
+            self.network['id'],
+            suffix=self.environment.hosts[0].dhcp_agent.get_namespace_suffix())
+        ip = ip_lib.IPWrapper(namespace)
+
+        devices = ip.get_devices()
+        self.assertEqual(1, len(devices))
+
+        dhcp_dev = devices[0]
+        mtu = dhcp_dev.link.mtu
+        self.assertEqual(1450, mtu)
+
+        mtu -= 1
+        self.safe_client.update_network(self.network['id'], mtu=mtu)
+        common_utils.wait_until_true(lambda: dhcp_dev.link.mtu == mtu)
+
 
 class TestDhcpAgentHA(BaseDhcpAgentTest):