Make this a configuration knob

config.yaml

@@ -111,3 +111,12 @@ options:
       which do not include a neutron-gateway (do not require l3, lbaas or vpnaas
       services) and should only be used in-conjunction with flat or VLAN provider
       networks configurations.
+  prevent-arp-spoofing:
+    type: boolean
+    default: true
+    description: |
+      Enable suppression of ARP responses that don't match an IP address that belongs
+      to the port from which they originate.
+      .
+      Only supported in OpenStack Liberty or newer, which as the required minimum version
+      of Open vSwitch.

hooks/neutron_ovs_context.py

@@ -58,6 +58,7 @@ class OVSPluginContext(context.NeutronContext):
         ovs_ctxt['use_syslog'] = conf['use-syslog']
         ovs_ctxt['verbose'] = conf['verbose']
         ovs_ctxt['debug'] = conf['debug']
+        ovs_ctxt['prevent_arp_spoofing'] = conf['prevent-arp-spoofing']
 
         net_dev_mtu = neutron_api_settings.get('network_device_mtu')
         if net_dev_mtu:

templates/liberty/ml2_conf.ini

@@ -30,12 +30,10 @@ bridge_mappings = {{ bridge_mappings }}
 tunnel_types = {{ overlay_network_type }}
 l2_population = {{ l2_population }}
 enable_distributed_routing = {{ distributed_routing }}
+prevent_arp_spoofing = {{ prevent_arp_spoofing }}
 {% if veth_mtu -%}
 veth_mtu = {{ veth_mtu }}
 {% endif -%}
-{% if not neutron_security_groups -%}
-prevent_arp_spoofing = False
-{% endif %}
 
 [securitygroup]
 {% if neutron_security_groups -%}

unit_tests/test_neutron_ovs_context.py

@@ -95,7 +95,8 @@ class OVSPluginContextTest(CharmTestCase):
                   'verbose': True,
                   'debug': True,
                   'bridge-mappings': "physnet1:br-data physnet2:br-data",
-                  'flat-network-providers': 'physnet3 physnet4'}
+                  'flat-network-providers': 'physnet3 physnet4',
+                  'prevent-arp-spoofing': False}
 
         def mock_config(key=None):
             if key:
@@ -140,6 +141,7 @@ class OVSPluginContextTest(CharmTestCase):
             'network_providers': 'physnet3,physnet4',
             'bridge_mappings': 'physnet1:br-data,physnet2:br-data',
             'vlan_ranges': 'physnet1:1000:1500,physnet2:2000:2500',
+            'prevent_arp_spoofing': False,
         }
         self.assertEquals(expect, napi_ctxt())
 
@@ -204,6 +206,7 @@ class OVSPluginContextTest(CharmTestCase):
             'overlay_network_type': 'gre',
             'bridge_mappings': 'physnet1:br-data',
             'vlan_ranges': 'physnet1:1000:2000',
+            'prevent_arp_spoofing': True,
         }
         self.assertEquals(expect, napi_ctxt())