diff --git a/instack_undercloud/tests/test_undercloud.py b/instack_undercloud/tests/test_undercloud.py
index 00abbd7df..6d91fc2a5 100644
--- a/instack_undercloud/tests/test_undercloud.py
+++ b/instack_undercloud/tests/test_undercloud.py
@@ -675,7 +675,7 @@ class TestGenerateEnvironment(BaseTestCase):
         env = undercloud._generate_environment('.')
         reference = [{"tag": "ctlplane-subnet", "gateway": "192.168.24.1",
                       "ip_range": "192.168.24.100,192.168.24.120",
-                      "netmask": "255.255.255.0"}]
+                      "netmask": "255.255.255.0", "mtu": 1500}]
         actual = json.loads(env['INSPECTION_SUBNETS'])
         self.assertEqual(reference, actual)
 
@@ -697,10 +697,10 @@ class TestGenerateEnvironment(BaseTestCase):
         env = undercloud._generate_environment('.')
         reference = [{"tag": "subnet1", "gateway": "192.168.10.254",
                       "ip_range": "192.168.10.100,192.168.10.189",
-                      "netmask": "255.255.255.0"},
+                      "netmask": "255.255.255.0", "mtu": 1500},
                      {"tag": "subnet2", "gateway": "192.168.20.254",
                       "ip_range": "192.168.20.100,192.168.20.189",
-                      "netmask": "255.255.255.0"}]
+                      "netmask": "255.255.255.0", "mtu": 1500}]
         actual = json.loads(env['INSPECTION_SUBNETS'])
         self.assertEqual(reference, actual)
 
diff --git a/instack_undercloud/undercloud.py b/instack_undercloud/undercloud.py
index 8788b7bf0..300365a6e 100644
--- a/instack_undercloud/undercloud.py
+++ b/instack_undercloud/undercloud.py
@@ -1309,6 +1309,7 @@ def _generate_inspection_subnets():
         env_dict['ip_range'] = s.inspection_iprange
         env_dict['netmask'] = str(netaddr.IPNetwork(s.cidr).netmask)
         env_dict['gateway'] = s.gateway
+        env_dict['mtu'] = CONF.local_mtu
         env_list.append(env_dict)
     return json.dumps(env_list)