We begin this chapter by examining the physical layout of the database, such as the Oracle processes and how they interact with the network. We move on to examining authentication and authorization and then move to the logical layout of the database.
This section describes the major components of Oracle and their interaction with the network. We begin with perhaps the most crucial network-facing component, the TNS Listener.
The TNS Listener is the hub of all communications in Oracle. “TNS” stands for Transparent Network Substrate and this is the protocol that Oracle uses to communicate between client and server. The TNS protocol is described on the Ethereal web site at http://www.ethereal.com/docs/dfref/t/tns.html.
The TNS Listener responds to a number of commands such as “version,” “status,” and “services,” and when a database server is first started, it registers with the TNS Listener using the service_register_NSGR command. This lets the TNS Listener know that the database server is ready to accept connections. Incidentally, although the service_register_NSGR command is intended to be used locally the command can be sent over the network. In the past there have been denial of service issues with this command that can kill the TNS Listener.
When a client wishes to access the database server, the client connects first to the Listener. The Listener replies back with a TCP port that ...