diff --git a/etc/neutron.conf b/etc/neutron.conf
index 13ff410c69a..99a3ca3761a 100644
--- a/etc/neutron.conf
+++ b/etc/neutron.conf
@@ -245,6 +245,9 @@
 #
 # CIDR of the administrative network if HA mode is enabled
 # l3_ha_net_cidr = 169.254.192.0/18
+#
+# Enable snat by default on external gateway when available
+# enable_snat_by_default = True
 # =========== end of items for l3 extension =======
 
 # =========== items for metadata proxy configuration ==============
diff --git a/neutron/db/l3_gwmode_db.py b/neutron/db/l3_gwmode_db.py
index 558adff15eb..8eabc9212a2 100644
--- a/neutron/db/l3_gwmode_db.py
+++ b/neutron/db/l3_gwmode_db.py
@@ -13,6 +13,7 @@
 #    under the License.
 #
 
+from oslo_config import cfg
 from oslo_log import log as logging
 import sqlalchemy as sa
 from sqlalchemy import sql
@@ -23,6 +24,12 @@ from neutron.extensions import l3
 
 
 LOG = logging.getLogger(__name__)
+OPTS = [
+    cfg.BoolOpt('enable_snat_by_default', default=True,
+                help=_('Define the default value of enable_snat if not '
+                       'provided in external_gateway_info.'))
+]
+cfg.CONF.register_opts(OPTS)
 EXTERNAL_GW_INFO = l3.EXTERNAL_GW_INFO
 
 # Modify the Router Data Model adding the enable_snat attribute
@@ -55,10 +62,8 @@ class L3_NAT_dbonly_mixin(l3_db.L3_NAT_dbonly_mixin):
         # Load the router only if necessary
         if not router:
             router = self._get_router(context, router_id)
-        # if enable_snat is not specified then use the default value (True)
-        enable_snat = not info or info.get('enable_snat', True)
         with context.session.begin(subtransactions=True):
-            router.enable_snat = enable_snat
+            router.enable_snat = self._get_enable_snat(info)
 
         # Calls superclass, pass router db object for avoiding re-loading
         super(L3_NAT_dbonly_mixin, self)._update_router_gw_info(
@@ -67,6 +72,13 @@ class L3_NAT_dbonly_mixin(l3_db.L3_NAT_dbonly_mixin):
         # method is overridden in child classes
         return router
 
+    @staticmethod
+    def _get_enable_snat(info):
+        if info and 'enable_snat' in info:
+            return info['enable_snat']
+        # if enable_snat is not specified then use the default value
+        return cfg.CONF.enable_snat_by_default
+
     def _build_routers_list(self, context, routers, gw_ports):
         for rtr in routers:
             gw_port_id = rtr['gw_port_id']
diff --git a/neutron/tests/unit/extensions/test_l3_ext_gw_mode.py b/neutron/tests/unit/extensions/test_l3_ext_gw_mode.py
index cba57a6bf84..0d4f7fcc62d 100644
--- a/neutron/tests/unit/extensions/test_l3_ext_gw_mode.py
+++ b/neutron/tests/unit/extensions/test_l3_ext_gw_mode.py
@@ -16,6 +16,7 @@
 
 import mock
 from oslo_config import cfg
+import testscenarios
 from webob import exc
 
 from neutron.common import constants
@@ -27,6 +28,7 @@ from neutron.db import models_v2
 from neutron.extensions import l3
 from neutron.extensions import l3_ext_gw_mode
 from neutron.openstack.common import uuidutils
+from neutron.tests import base
 from neutron.tests.unit.db import test_db_base_plugin_v2
 from neutron.tests.unit.extensions import test_l3
 from neutron.tests.unit import testlib_api
@@ -74,6 +76,33 @@ class TestDbSepPlugin(test_l3.TestL3NatServicePlugin,
     supported_extension_aliases = ["router", "ext-gw-mode"]
 
 
+class TestGetEnableSnat(testscenarios.WithScenarios, base.BaseTestCase):
+    scenarios = [
+        ('enabled', {'enable_snat_by_default': True}),
+        ('disabled', {'enable_snat_by_default': False})]
+
+    def setUp(self):
+        super(TestGetEnableSnat, self).setUp()
+        self.config(enable_snat_by_default=self.enable_snat_by_default)
+
+    def _test_get_enable_snat(self, expected, info):
+        observed = l3_gwmode_db.L3_NAT_dbonly_mixin._get_enable_snat(info)
+        self.assertEqual(expected, observed)
+
+    def test_get_enable_snat_without_gw_info(self):
+        self._test_get_enable_snat(self.enable_snat_by_default, {})
+
+    def test_get_enable_snat_without_enable_snat(self):
+        info = {'network_id': _uuid()}
+        self._test_get_enable_snat(self.enable_snat_by_default, info)
+
+    def test_get_enable_snat_with_snat_enabled(self):
+        self._test_get_enable_snat(True, {'enable_snat': True})
+
+    def test_get_enable_snat_with_snat_disabled(self):
+        self._test_get_enable_snat(False, {'enable_snat': False})
+
+
 class TestL3GwModeMixin(testlib_api.SqlTestCase):
 
     def setUp(self):