How do I restrict or allow a few client machines to connect to Server ?

In my setup I want to restrict the use of oracle Database based on ip address.
My Database and OS detalis :
Database Version : 10.2.0.1.0
OS : Linux

Into the sqlnet.ora file,below These parameters enable to configure access control to the database,

TCP.EXCLUDED_NODES=(finance.us.acme.com, mktg.us.acme.com, 144.25.5.25)
TCP.INVITED_NODES=(sales.us.acme.com, hr.us.acme.com, 144.185.5.73)
TCP.VALIDNODE_CHECKING=yes|no

hence this solution is not working at my end...Database is accessed easily by excluded_node.
Can anyone suggest me what so reason behind that...

Thanks....