If no active AA ISA is available (for example, because of an operational failure, misconfiguration) the default behavior is to forward traffic as if no AA was configured, the system does not send traffic to the AA ISA (equivalent to fail to closed). Alarms are raised to flag this state externally. There is an optional ‟fail to open” feature where AA ISA service traffic is dropped if no active AA ISA is present (such as no AA ISA is present and operationally up).