diff --git a/roles/configure_functional_tests/tasks/main.yaml b/roles/configure_functional_tests/tasks/main.yaml
index 6f7f798d619..799db6998b3 100644
--- a/roles/configure_functional_tests/tasks/main.yaml
+++ b/roles/configure_functional_tests/tasks/main.yaml
@@ -1,3 +1,9 @@
+- name: Set optional env vars
+  set_fact:
+    override_env:
+      OVN_BRANCH: "{{ OVN_BRANCH | default(omit) }}"
+      OVS_BRANCH: "{{ OVS_BRANCH | default(omit) }}"
+
 - shell:
     cmd: |
         set -e
@@ -13,8 +19,6 @@
         TOP_DIR={{ devstack_dir }}
         VENV={{ tests_venv }}
         STACK_USER=stack
-        OVS_BRANCH={{ OVS_BRANCH }}
-        OVN_BRANCH={{ OVN_BRANCH }}
         Q_BUILD_OVS_FROM_GIT={{ Q_BUILD_OVS_FROM_GIT }}
         MEMORY_TRACKER={{ MEMORY_TRACKER }}
         INSTALL_OVN={{ INSTALL_OVN }}
@@ -22,8 +26,6 @@
         DATABASE_USER=openstack_citest
         MYSQL_GATHER_PERFORMANCE={{ MYSQL_GATHER_PERFORMANCE | default(true) }}
 
-        source $DEVSTACK_PATH/functions
-        source $DEVSTACK_PATH/lib/neutron_plugins/ovn_agent
         source $NEUTRON_DIR/tools/configure_for_func_testing.sh
 
         if is_fedora; then
@@ -43,3 +45,4 @@
         configure_host_for_func_testing
 
     executable: /bin/bash
+  environment: "{{ override_env | default({})}}"
diff --git a/tools/configure_for_func_testing.sh b/tools/configure_for_func_testing.sh
index 692b4793573..5c6fc2b2cae 100755
--- a/tools/configure_for_func_testing.sh
+++ b/tools/configure_for_func_testing.sh
@@ -67,9 +67,12 @@ INSTALL_MYSQL_ONLY=${INSTALL_MYSQL_ONLY:-False}
 # The gate should automatically install dependencies.
 INSTALL_BASE_DEPENDENCIES=${INSTALL_BASE_DEPENDENCIES:-$IS_GATE}
 INSTALL_OVN=${INSTALL_OVN:-True}
-OVN_BRANCH=${OVN_BRANCH:-main}
+OVN_BRANCH=${OVN_BRANCH:-v21.06.0}
 Q_BUILD_OVS_FROM_GIT=${Q_BUILD_OVS_FROM_GIT:-True}
-OVS_BRANCH=${OVS_BRANCH:-master}
+# OVS_BRANCH needs to be updated along with OVN_BRANCH, ovs is
+# being used as submodule in ovn repo, to get a working ovs
+# version can use git submodule status command on ovn repo
+OVS_BRANCH=${OVS_BRANCH:-a4b04276ab5934d087669ff2d191a23931335c87}
 
 
 if [ ! -f "$DEVSTACK_PATH/stack.sh" ]; then
diff --git a/zuul.d/base.yaml b/zuul.d/base.yaml
index 5b62854a9c5..3c07258bc26 100644
--- a/zuul.d/base.yaml
+++ b/zuul.d/base.yaml
@@ -39,8 +39,6 @@
       Q_BUILD_OVS_FROM_GIT: True
       MEMORY_TRACKER: True
       INSTALL_OVN: True
-      OVN_BRANCH: v21.06.0
-      OVS_BRANCH: "a4b04276ab5934d087669ff2d191a23931335c87"
       devstack_services:
         # Ignore any default set by devstack. Emit a "disable_all_services".
         base: false