Lesson 18

This module discussed how the TNS listener functions on an Oracle server and how to create a listener.ora file.
You should also understand how to use the LSNRCTL and TCPCTL utilities to start and stop a listener, and how to use the LSNRCTL help facility for assistance with the command syntax. Now that we have seen how the Oracle server is configured to accept connections, we'll take a look in the next module at how Oracle clients are configured.

The following Oracle Net configuration options resolve the service name the client specifies into the host and instance names needed to reach an Oracle database: Local name resolution. For local name resolution, you install a file called TNSNAMES.ORA on each client machine that contains entries that provide the host and Oracle instance for each Oracle Net alias. You must maintain this file on the client machines if any changes are made to the underlying database locations. Your network topology is almost certain to change over time, so use of this option can lead to an increased maintenance load. If you are using Oracle Internet Directory, described later in this section, you do not need a TNSNAMES.ORA file.

Oracle Names was supported in earlier Oracle releases, providing a way to eliminate the need for a TNSNAMES.ORA file on each client, that was the good part. The bad part was that Oracle Names was a proprietary solution. Since Oracle Internet Directory is based on standards and provides this functionality, Oracle declared Oracle Names obsolete after the Oracle9i release.

The need for a centralized naming service extends far beyond the Oracle environment. In fact, there is a well-defined standard for accessing this type of information, the Lightweight Directory Access Protocol (LDAP). As of the Oracle Database 11g release, Oracle Internet Directory (OID) is a part of Fusion Middleware. OID is an LDAP-enabled directory that can fulfill the same role as the previously available Oracle Names service. The OID is also used for a variety of other purposes, such as enabling single sign-on for the Oracle Application Server Portal product. Since Oracle Database 10g, you can export directory entries to create a local TNSNAMES.ORA file; this file may be used for clients not using the directory or if the directory is unavailable.

Clients can simply use the name of the host on which the instance runs. This is valid for TCP/IP networks with a mechanism in place for resolving the hostname into an IP address. For example, the Domain Name Service (DNS) translates a hostname into an IP address, much as Oracle Names translates service names. Since Oracle Database 10g, you can use this method with either a host name, domain-qualified if appropriate, or a TCP/IP address, but the connection will not support advanced services such as connection pooling.

Oracle Net can interface with external or third-party naming and authentication services such as Kerberos or Radius. Use of such services may require Oracle Advanced Security (known as the Advanced Networking Option prior to Oracle8i).

Before moving on to the next module, click the Quiz link below to check your mastery of listener concepts with a short multiple-choice quiz.
Oracle Listener Concepts - Quiz