To prevent every one to connect to Oracle database directly, we can just authorize the specified list of IP addresses, for example IP of application servers and legal IPs.
We can just deal with two options in the file SQLNET.ORA Oracle database server side.
Step 1: Enable the control and the check of the IPs addresses:
tcp.validnode_checking = yes
Step 2: Black list
tcp.excluded_nodes = (172.16.1.122,172.16.1.1)
Note: Authorize any one and just blocks theses two IP addresses.
Step 2: White List
tcp.invited_nodes = (172.16.1.122,172.16.1.1)
Note: Authorize just theses IP addresses and blocks others
Step 3: Reload listener
$ lsnrctl reload