diff --git a/devstack/lib/ml2 b/devstack/lib/ml2
index 3dde13ec091..936e8d4b0f5 100644
--- a/devstack/lib/ml2
+++ b/devstack/lib/ml2
@@ -17,3 +17,16 @@ function configure_ml2 {
         fi
     done
 }
+
+function configure_ml2_extension_drivers {
+    if is_neutron_legacy_enabled; then
+        # NOTE(yamamoto): This overwrites what neutron-legacy set,
+        # with the latest set of drivers.
+        # While we modifies Q_ML2_PLUGIN_EXT_DRIVERS (via
+        # neutron_ml2_extension_driver_add calls) in the post-config phase,
+        # lib/neutron-legcay populates this in "configure_neutron", which is
+        # before post-config.
+        # REVISIT(yamamoto): Probably this ought to be in lib/neutron-legcay
+        iniset /$NEUTRON_CORE_PLUGIN_CONF ml2 extension_drivers ${Q_ML2_PLUGIN_EXT_DRIVERS}
+    fi
+}
diff --git a/devstack/plugin.sh b/devstack/plugin.sh
index 0d4ce8d01b6..032640cc860 100644
--- a/devstack/plugin.sh
+++ b/devstack/plugin.sh
@@ -19,6 +19,14 @@ fi
 if [[ "$1" == "stack" ]]; then
     case "$2" in
         install)
+            if [[ "$NEUTRON_AGENT" == "openvswitch" ]] && \
+               [[ "$Q_BUILD_OVS_FROM_GIT" == "True" ]]; then
+                remove_ovs_packages
+                compile_ovs True /usr /var
+                start_new_ovs
+            fi
+            ;;
+        post-config)
             if is_service_enabled q-flavors neutron-flavors; then
                 configure_flavors
             fi
@@ -30,21 +38,11 @@ if [[ "$1" == "stack" ]]; then
             fi
             if is_service_enabled q-dns neutron-dns; then
                 configure_dns_extension
+                post_config_dns_extension
             fi
             if is_service_enabled neutron-segments; then
                 configure_segments_extension
             fi
-            if [[ "$NEUTRON_AGENT" == "openvswitch" ]] && \
-               [[ "$Q_BUILD_OVS_FROM_GIT" == "True" ]]; then
-                remove_ovs_packages
-                compile_ovs True /usr /var
-                start_new_ovs
-            fi
-            ;;
-        post-config)
-            if is_service_enabled q-dns neutron-dns; then
-                post_config_dns_extension
-            fi
             if is_service_enabled q-agt neutron-agent; then
                 configure_l2_agent
             fi
@@ -58,6 +56,9 @@ if [[ "$1" == "stack" ]]; then
                 configure_l2_agent
                 configure_l2_agent_sriovnicswitch
             fi
+            if [ $NEUTRON_CORE_PLUGIN = ml2 ]; then
+                configure_ml2_extension_drivers
+            fi
             ;;
         extra)
             if is_service_enabled q-sriov-agt neutron-sriov-agent; then