Net Listener Features

Oracle Network Services, a pivotal component of the Oracle Database, provides the mechanisms to ensure that client-server and server-server communication can happen seamlessly and securely. A crucial component of this is the Oracle Net Listener, often just called the "listener". The listener is responsible for serving incoming client connection requests. For a client to successfully connect to an Oracle server, several features and configurations of the Net Listener are imperative:

1. Listener Configuration (listener.ora)
   
   1. Listener Name: By default, the listener name is `LISTENER`. It's the identifier for the listener process on the server.
   2. Protocol Address: Defines the network protocols the listener supports and the addresses it listens on. Examples include TCP/IP, IPC
   3. Service Name: Identifies the database service(s) for which it is listening. This must match the service name clients use in their connection string.
2. Dynamic Service Registration:
   Service Registration: Modern Oracle Databases register themselves with the listener, making manual configuration of services in listener.ora often unnecessary. This self-registration includes crucial details like instance names, service names, and workload information.
3. Connection Endpoints: Endpoint Configuration: Ensure that the endpoints for the desired protocols (TCP, IPC, etc.) are correctly configured in listener.ora, specifying the appropriate IP addresses and port numbers.
4. Security
   
   1. Listener Password**: Protects against unauthorized management tasks against the listener. Setting a password restricts the ability to start/stop the listener or get its status.
   2. Valid Node Checking**: If activated, the listener will verify that connection requests are from valid nodes defined in the `sqlnet.ora` file.
   3. Encryption and Integrity**: For secure communications, the listener can be set up to support native network encryption and data integrity. This ensures that data is encrypted as it travels over the network and that it has not been tampered with during transmission.
5. Load Balancing & Failover:
   
   1. Connection Load Balancing: Directs client requests to the least loaded instance, distributing client connections efficiently.
   2. Transparent Application Failover (TAF): This is an automatic client failover mechanism for high availability environments.
6. Diagnostics & Logging:
   
   1. Logging: For diagnostic and auditing purposes, the listener logs events in a listener log file. Ensure that the logging parameters, such as `LOG_DIRECTORY` and `LOG_FILE`, are appropriately set.
   2. Trace Level: For detailed troubleshooting, one can set different trace levels (`TRACE_LEVEL`) to capture more granular information about the listener's operation.
7. Backward Compatibility:
   If older clients are connecting, ensure the listener is compatible by verifying the version and adjusting parameters like `USE_PLUG_AND_PLAY` accordingly.

To establish a successful connection from the client to the server, the client connection string must also be correctly configured (typically in the `tnsnames.ora` file) to reference the correct service name, protocol, and endpoint details. In conclusion, ensuring the effective operation and configuration of Oracle Net Listener is imperative for seamless client-server communication. Periodic reviews and monitoring of the listener's configuration and logs can help preemptively address issues and ensure optimal performance and security.

Oracle is constantly making enhancements to Net, and the Net listener is no exception. The Oracle listener still serves the same basic function of listening for incoming database connections and establishing connections to the Oracle database, but the enhancements in Oracle provide more robust listener-process management and more reliability, as described in the list below.

1. New initialization parameters: To take advantage of many of the new features of Net, you must add some new initialization parameters, such as SERVICES_NAMES and INSTANCE_NAMES, when starting up your database.
2. Changes to the tnsnames.ora file format: The file that specifies which database nodes are available through Net listener has been revised to handle new features of Net.
3. Net Configuration Assistant: This assistant has been enhanced to support new Net and Oracle features so that it can be used to configure listeners, naming methods, Net service names, and LDAP directory service.
4. Multiple services for one database instance: The service name replaces the service identification (SID) in Oracle. This allows one database instance to have several services, enabling a listener to access the database as if it were two databases.
5. Multiple database instances for one service: Oracle uses the service name to consolidate many databases into one service. A service can connect database instances on different nodes.

The next lesson looks at Net Services scalability features.

Oracle Net Services provides enterprise wide connectivity solutions in distributed, heterogeneous computing environments. Oracle Net Services ease the complexities of network configuration and management, maximize performance, and improve network diagnostic capabilities. This module introduces the basic networking concepts involved in a typical network configuration. The topics include:

1. Connectivity
2. Manageability
3. Internet and Intranet Scalability
4. Performance Between the Middle Tier and Oracle Database
5. Network Security

Oracle Net, a component of Oracle Net Services, enables a network session from a client application to an Oracle Database server. Once a network session is established, Oracle Net acts as the data courier for both the client application and the database server. It is responsible for establishing and maintaining the connection between the client application and database server, as well as exchanging messages between them. Oracle Net is able to perform these jobs because it is located on each computer in the network.