Oracle Clients timeout after some IDLE time? Run this test:

Idle time test

　
1)  Establish a SQL*Plus connection to the instance:

　

sqlplus username@tns alias

password:

　

2)  Leave this SQL session idle for an hour.

　

Don't issue any commands, queries or generate any activity for an hour.

In other words, walk away and leave this client session idle for at least 1 hour.

　

3)  Return to the client and issue a simple select statement:

　

select * from dual;

This connection should be alive and return results. 

4)  See the following document:

Resolving Problems with Connection Idle Timeout With Firewall (Doc ID 257650.1)