Stale flows in ACL tables specific to security rules are observed when events received by neutronvpn and ACL are as specified below:

(1) Neutron Port Event

(2) Neutron SG Event

(3) ACL Interface/State Event

(4) ACL Event (accesslist-acl)

There would not be stale flows if the order of events is (1) (3) (2) (4), but if the events received are in order (1) (2) (3) (4), the flows specific to Security rule are left over in the ACL tables.