Reviewing the documentation 12c in the part referring to the configuration of the listeners I see the possible states in which You can find the listener. It has gone from four (in previous versions) to five.
The new state is Restricted, the listener now reports when the database is in restricted mode.
From the Oracle Documentacion 12c
The status field indicates if the instance can accept connections.
- READY means that the instance can accept connections.
- BLOCKED means that t he instance cannot accept connections.
- READY/SECONDARY means that this is a secondary instance in an Oracle Real Application Clusters primary/secondary configuration, and is ready to accept connections.
- RESTRICTED means the instance is in restricted mode. The listener blocks all connections to this instance.
- UNKNOWN means that the instance is registered statically in the listener.ora file rather than dynamically with service registration. Therefore, the status is not known.
HTH – Antonio NAVARRO