ORACLE 11G LISTENER's NET SERVICE CONCEPTS

ORACLE  NET SERVICES

Oracle Net, a component of Oracle Net Services, enables a network session from a client application to an Oracle Database server. When a network session is established, Oracle Net acts as the data courier for both the client application and the database.

Oracle Net is a software component that resides on both the client and the database server. Oracle Net is layered on top of network Oracle protocol support, rules that determine how applications access the network and how data is subdivided into packets for transmission across the network.

Oracle Net has two software components:

·         Oracle Net Foundation Layer

·         Oracle Protocol Support

Oracle Net Foundation Layer

On the client side, applications communicate with Oracle Net foundation layer to establish and maintain connections.

A network protocol sends client request information to an Oracle protocol support layer, which then sends information to the Oracle Net foundation layer. The Oracle Net foundation layer then communicates with the Oracle Database server to process the client request.

Oracle Protocol Support

The Oracle Net foundation layer uses Oracle protocol support to communicate with the following industry-standard network protocols:

·         TCP/IP (version 4 and version 6)

·         TCP/IP with SSL

·         Named Pipes

·         SDP

One of the most common connect identifiers is a net service name, a simple name for a service. The following CONNECT command uses a connect string that uses net service name sales as the connect identifier:

SQL> CONNECT hr@DB11G

Enter password: password

When net service name DB11G is used, connection processing takes place by first mapping DB11G to the connect descriptor. This mapped information is accessed by naming methods. The following naming methods are available:

·     Local naming

·     Directory naming

·     Easy Connect naming

·     External naming

Using localized management, network address information is stored in tnsnames.ora files on each computer in the network. Using centralized management, network address information is stored in centralized directory server.

OSI Communication Layers

Configuring Service Registration

Service registration allows processes, such as an Oracle database, to identify their available services to the listener, which then acts as a port mapper for those services. The listener uses the dynamic service information about the database and instance received through service registration before using statically configured information in the listener.ora file.
Dynamic service registration is configured in the database initialization file. It does not require any configuration in the listener.ora file. However, listener configuration must be set to listen on the ports named in the database initialization file, and must not have parameters set that prevent automatic registration, such as COST parameters

Setting Initialization Parameters for Service Registration

To ensure service registration works properly, the initialization parameter file should contain the following parameters:

·     SERVICE_NAMES for the database service name

·     INSTANCE_NAME for the instance name

·     LOCAL_LISTENER for the local listener

·         REMOTE_LISTENER for the remote listener

Registering Information with a Local Listener

·         By default, the PMON process registers service information with its local listener on the default local address of TCP/IP, port 1521. If the listener configuration is synchronized with the database configuration, then PMON can register service information with a nondefault local listener or a remote listener on another node. Synchronization occurs when the protocol address of the listener is specified in the listener.ora file and the location of the listener is specified in the initialization parameter file.

·         To have PMON register with a local listener that does not use TCP/IP, port 1521, configure the LOCAL_LISTENER parameter in the initialization parameter file to locate the local listener.

ALTER SYSTEM SET LOCAL LISTENER=["]listener_address["][,...];

In the preceding command, listener_address is resolved to the listener protocol addresses through a naming method, such as a tnsnames.ora file on the database server.

Monitoring Services of a Listener

The SERVICES command of the Listener Control utility provides detailed information about the services and instances registered with a listener and the service handlers allocated to each instance. To show information about the services and instances from the command line, enter:

lsnrctl SERVICES [listener_name]