diff --git a/neutron_tempest_plugin/api/base.py b/neutron_tempest_plugin/api/base.py
index 5a1de9c..77f3f68 100644
--- a/neutron_tempest_plugin/api/base.py
+++ b/neutron_tempest_plugin/api/base.py
@@ -1225,6 +1225,16 @@
         client = client or ndp_proxy.get('client') or cls.client
         client.delete_ndp_proxy(ndp_proxy['id'])
 
+    @classmethod
+    def get_loaded_network_extensions(cls):
+        """Return the network service loaded extensions
+
+        :return: list of strings with the alias of the network service loaded
+                 extensions.
+        """
+        body = cls.client.list_extensions()
+        return [net_ext['alias'] for net_ext in body['extensions']]
+
 
 class BaseAdminNetworkTest(BaseNetworkTest):
 
diff --git a/neutron_tempest_plugin/api/test_subnets.py b/neutron_tempest_plugin/api/test_subnets.py
index 126dc70..663713c 100644
--- a/neutron_tempest_plugin/api/test_subnets.py
+++ b/neutron_tempest_plugin/api/test_subnets.py
@@ -69,6 +69,8 @@
 
     @decorators.idempotent_id('c0f9280b-9d81-4728-a967-6be22659d4c8')
     def test_list_validation_filters(self):
+        if 'subnet-external-network' in self.get_loaded_network_extensions():
+            self.list_kwargs['router:external'] = False
         self._test_list_validation_filters(self.list_kwargs)
         self._test_list_validation_filters({
             'unknown_filter': 'value'}, filter_is_valid=False)