Lesson 1

To be useful, a database must be accessible from computers other than the one on which the database resides. Oracle supplies Oracle Net Services for this purpose. Oracle Net consists of a

1. listener and
2. a set of network adaptors

that allow client software to communicate with Oracle databases using a standard networking protocol knwon as TCP/IP . Oracle Net exists to provide a common interface to client applications that need to connect to an Oracle database. Applications are written to use Oracle Network Services which takes care of dealing with the underlying network protocols that are being used. Thus, the same client application that runs in a TCP/IP environment can run in an SPX/IPX^[1] environment, in an LU6.2 environment, and so forth. This module will show you how to configure Oracle Net so that you can connect to your COIN instance from any computer with Oracle client software installed. You will learn about the three key Oracle Net configuration files:

1. listener.ora,
2. tnsnames.ora, and
3. sqlnet.ora.

You also will learn about the listener control program, and how it can be used to stop and start the listener, and monitor listener status. Finally, you will learn how to use the Oracle Net Config software to configure a client PC so that it recognizes, and can connect to, your COIN database.

1. Oracle Net: Oracle's generic networking protocol, used to connect two databases to each other, or to connect client software to a database server. Oracle Net insulates Oracle and client applications from the underlying network protocol being used.
2. listener: A process that runs on a database server, and listens for incoming requests from clients that want to connect to databases on that server.
3. network adaptor: A Oracle Net component that adapts the Oracle Net software for a particular networking protocal. For example, the Oracle Net TCP/IP adaptor allows you to run Oracle Net over a TCP/IP network.
4. TCP/IP: A networking protocal widely used in the UNIX world, and which happens to be the most commonly used protocol by clients that need to connect to Oracle servers.
5. SPX/IPX: A networking protocol used on Novel NetWare networks.
6. LU6.2: A networking protocol used in IBM mainframe environments.

Listeners and network adaptors play crucial roles in enabling client software to communicate with Oracle databases over a network. Here's how they work together:

1. Listener:
   • The listener is a process that runs on the server machine where the Oracle database resides.
   • It listens for incoming connection requests from client software on various network protocols, such as TCP/IP or Oracle Net.
   • When a connection request is received, the listener establishes a connection with the client and forwards the request to the appropriate database instance.
2. Network Adaptor:
   • A network adaptor (also known as a network interface card or NIC) is a hardware device installed on both the server and client machines
   • It provides the physical connection between the machines over a network, such as a local area network (LAN) or the internet.
   • The network adaptor converts data into electrical signals and transmits them over the network cable or wireless connection.
3. Client Software Communication:
   • Client software, such as Oracle SQL Developer or other database tools, initiates a connection to the Oracle database by specifying the hostname or IP address of the server machine and the port number where the listener is running.
   • The client software sends a connection request to the listener using the network adaptor.
   • The listener receives the request and forwards it to the database instance specified in the connection string.
   • Once the connection is established, the client software can send SQL queries and other commands to the database, and receive results back from the database.

In summary, the listener acts as a gatekeeper, receiving connection requests from client software and directing them to the appropriate database instance. The network adaptor provides the physical means for data transmission between the client and server machines, allowing the client software to communicate with the Oracle database over the network.

By the end of this module, you will be able to:

1. Edit the listener.ora file, and add an entry for another database instance
2. Edit the tnsnames.ora file, and add a new service name for use by client software
3. Use the ping command to verify connectivity to the host
4. Use the tnsping command to verify connectivity to the Oracle Net listener
5. Start and stop the Oracle Net listener
6. Connect to a remote database over the network

[1]IPX/SPX: **/ IPX/SPX stands for Internetwork Packet Exchange/Sequenced Packet Exchange. It's a suite of networking protocols developed by Novell for its NetWare operating system.