Understanding SQL*Net
Common Sources of Error: Configuration Files
The most common cause of problems in making a SQL*Net connection is in the structure or location of the configuration files.
Syntax Errors
The syntax of the files must be followed precisely. If you create the files using Network Manager, syntax errors should not occur. However, if you create or edit them by hand, check them carefully to see that all the appropriate parentheses are in place, that the lines are indented to show their logical structure, and that there are no typographical errors. See Appendix B, "Syntax Rules for Configuration Files," for details on the syntax of these files. Be sure that all service names are mapped to connect descriptors in the TNSNAMES. ORA file.
Location Errors
The TNSNAMES.ORA file must be distributed so that it is available to all nodes that make connections using SQL*Net version 2 (unless Oracle Names is being used on the network).
A unique LISTENER.ORA file must be distributed to each node that includes one or more databases.
In a network that includes one or more Interchanges, a unique TNSNAV.ORA file must be available to all the clients which have similar navigation requirements.
Every node with an Interchange must have an INTCHG.ORA, a TNSNET.ORA, and a TNSNAV.ORA file.
See the Oracle operating system specific manual for your platform for the exact locations of these files.