If I have a limited number of db clients which are authorized to access my listener, I can restrict access to my listener by setting only two parameters in sqlnet.ora.
TCP.VALIDNODE_CHECKING = yes TCP.INVITED_NODES = (dbclient001,chltlxlsc1)
chltlxlsc1 is my db server, I include it in the list, it is required to start the listener locally.
From dbclient001, I can connect :
$ sqlplus scott/tiger@lsc02 SQL*Plus: Release 10.1.0.4.2 - Production on Wed Nov 22 09:47:43 2006 Copyright (c) 1982, 2005, Oracle. All rights reserved. Connected to: Oracle9i Enterprise Edition Release 18.104.22.168.0 - Production With the Partitioning option JServer Release 22.214.171.124.0 - Production
From dbclient002, I cannot connect
$ sqlplus scott/tiger@lsc02 SQL*Plus: Release 10.1.0.4.2 - Production on Wed Nov 22 09:48:26 2006 Copyright (c) 1982, 2005, Oracle. All rights reserved. ERROR: ORA-12547: TNS:lost contact