Originally, the listener does not set any limits on connecting to the database and serves all requests, while security and blocking are done through the database or applications, so that some devices and subnetworks are prevented from connecting to the database. But we can control through the listener by specifying some directions in the SQLNET.ORA file that is located in the server in the same path as the LISTENER.ORA file. We can specify some directions in this file through which we can control access to the database. These directions are:

TCP.VALIDNODE_CHECKING

TCP.EXCLUDED_NODES

TCP.INVITED_NODES

TCP.VALIDNODE_CHECKING It originally takes the value NO, which means that other directions are ignored, but the value must be changed to YES To enable the database access control process, if TCP.VALIDNODE_CHECKING is set to YES, other directions will be enabled which is TCP.INVITED_NODES, which contains a list of NODES, which are devices or a group of addresses that will be allowed to connect to the database Data All other NODES will be prevented from connecting to the database through the listener, as for TCP.EXCLUDED_NODES, it includes a list of NODES that should be prevented from connecting to the database, so it is necessary to specify one of the lists (TCP.EXCLUDED_NODES or TCP.INVITED_NODES) if TCP.VALIDNODE_CHECKING takes the value yes, but if both lists are specified and there is a conflict The TCP.INVITED_NODES list has priority.