Sqlnet.ora : $ORACLE_HOME/network/admin
TCP.EXCLUDED_NODES
Purpose
Use the parameter TCP.EXCLUDED_NODES to specify which clients are denied access to the database.
Example
TCP.EXCLUDED_NODES=(finance.us.acme.com, mktg.us.acme.com, 144.25.5.25)
TCP.INVITED_NODES
Purpose
Use the parameter TCP.INVITED_NODES to specify which clients are allowed access to the database.
This list takes precedence over the TCP.EXCLUDED_NODES parameter if both lists are present.
Example
TCP.INVITED_NODES=(sales.us.acme.com, hr.us.acme.com, 144.185.5.73)
TCP.VALIDNODE_CHECKING
Purpose
Use the parameter TCP.VALIDNODE_CHECKING to check for the TCP.INVITED_NODES and TCP.
EXCLUDED_NODES to determine which clients to allow or deny access.
Example
TCP.VALIDNODE_CHECKING=yes
TCP.VALIDNODE_CHECKING=no
Simple Way to keep your database Clean . you maybe need to restart your Listener after this
Thank you
Osama Mustafa