4.6. Summary
You need to understand several key components in order to succeed when networking in an Oracle environment. The main responsibilities of the DBA include determining the applications and type of connections that will be supported, the number of users and the locations from which they will be accessing the network, and the security issues involved in protecting sensitive information, such as single sign-on and data encryption.
In addition, you need to choose from the three basic types of network configurations when setting up an Oracle network: single-tier architecture, two-tier architecture, and n-tier architecture. Because systems have evolved from the simpler single-tier architecture to the more complex n-tier architecture, which can include connections through middle-tier servers and the Internet, you will most likely choose between the two architectures that Oracle Net is an integral part of: two-tier or n-tier.
Oracle Net manages the flow of information from client computers to Oracle servers and forms the foundation of all networked computing in the Oracle environment. Oracle Net provides services that can be divided into five main categories: connectivity, directory services, scalability, security, and accessibility. Connectivity solutions include support for multiple protocols, multiple operating systems, and Java and Internet. Directory services provide an infrastructure to resolve Oracle service names through a centralized naming repository. Scalability solutions include Connection Manager and Oracle Shared Server. Security options include Oracle Advanced Security, which provides an additional layer of security options and robust support for many varieties of firewalls. Accessibility support includes Heterogeneous Services and support for calling external procedures. Oracle Net also provides connectivity to Java stored procedures and URL connections.
The listener is the main server-side component in the Oracle Net environment. Listener configuration information is stored in the listener.ora file, and you manage the listener using the lsnrctl command-line utility. You configure the listener by using the Oracle Net Manager. The Oracle Net Manager provides a graphical interface for creating most of the Oracle Net files that you will use for Oracle, including the listener.ora file. If multiple listeners are configured, each one has a separate entry in the listener.ora file.
Oracle10g provides a feature called dynamic service registration. This feature allows an Oracle instance to automatically register itself with a listener. The listener must be configured with TCP/IP and listen on port 1521, or you must specify the parameter LOCAL_LISTENER in the init.ora file. You must set the parameters INSTANCE_NAME and SERVICE_NAMES in the init.ora file for the Oracle instance to enable dynamic service registration.
You can configure logging and tracing on the Oracle server using Oracle Net Manager, Oracle Enterprise Manager, or the lsnrctl utility. Logging records significant events, such as starting and stopping the listener, along with certain kinds of network errors. Errors are generated in the log in the form of an error stack. Tracing records all events that occur even when an error does not happen. The trace file provides a great deal of information that logs do not. Tracing uses much more space than logging and can also have an impact on system performance. Enable tracing only if other methods of troubleshooting fail to resolve the problem.
Configuring the Oracle server components correctly is the first step to successfully implementing Oracle in a network environment. If you do not have the Oracle server network components configured correctly, you will be unable to provide connection support to clients in the Oracle environment. Configure and test the server network components before configuring the Oracle clients.
Depending on your network environment, the client configuration setups can vary from no work to configuring a number of files on the client. The names resolution methods available for clients include hostnaming, Oracle Easy Connect, localnaming, Oracle Internet Directory, and External Naming. Hostnaming, which can only be used if you are using TCP/IP, is mainly used for simple Oracle networks. Oracle Easy Connect is an extension of hostnaming and allows for the inclusion of additional information such as the hostname and port specification. Localnaming is the most popular of the names resolution methods, and it uses the tnsnames.ora file, which is typically located on each client, to resolve net service names. The client looks up the net service name in the tnsnames.ora file and uses the resulting connect descriptor information to connect to the Oracle server. The hostnaming and localnaming methods are configured using the Oracle Net Manager or Oracle Enterprise Manager. Oracle Internet Directory is a Lightweight Directory Access Protocol (LDAP)–compliant server that provides for centralized management of Oracle database connection identifier information. External Naming uses a non-Oracle facility, such as DNS, to manage and resolve Oracle service names.
It is important to know how to troubleshoot connection problems. You should know the general format and content of the tnsnames.ora and sqlnet.ora files to be able to identify syntax errors. You should know where these files reside on the client. You should understand how the various names resolution methods work. You should become familiar with the tools that can be used, such as the TCP/IP-supplied ping utility and the Oracle-supplied tnsping utility to assist you when troubleshooting these problems. Finally, you should familiarize yourself with the most common Oracle error messages that can occur as a result of connection problems.
This chapter provides the foundation of knowledge that you will need when you are designing, configuring, and managing the Oracle network infrastructure. The decisions you make about the network design have ramifications in terms of the scalability, security, and flexibility of your Oracle environment. When you understand the underlying network architecture, network options available to you, and how to configure and manage the Oracle Net infrastructure, you will be able to provide consistent and reliable connections to Oracle services for your clients.