[Oracle] how to use a trigger to restrict user logon by IP Address

The following is an example of a trigger:
Copy codeThe Code is as follows:
Create or replace trigger logon_ip_control
After logon database
Declare
Ip STRING (30 );
User STRING (30 );
Begin
SELECT SYS_CONTEXT ('userenv', 'session _ user') into USER from dual;
SELECT SYS_CONTEXT ('userenv', 'IP _ address') into IP from dual;
If user = 'epay _ user'
THEN
IF ip not in ('192. 168.219.20 ', '192. 168.219.22 ')
THEN raise_application_error (-20001, 'user' | User | 'is not allowed to connect from' | ip );
End if;
End if;
End;
/

This trigger imposes IP restrictions on the user EPAY_USER (only '192. 168.219.20 ', '192. 168.219.22' are allowed. If you need to set an IP segment, use % or? For example, '192. 192.% ').
Here are a few examples to test:
1) login from an unauthorized IP address (192.168.219.21), connection failed
Copy codeThe Code is as follows:
[Oracle @ lxdb2 ~] $ Sqlplus epay_user @ pri
SQL * Plus: Release 11.2.0.3.0 Production on Wed Jul 3 19:23:48 2013
Copyright (c) 1982,201 1, Oracle. All rights reserved.
Enter password:
ERROR:
ORA-00604: error occurred at recursive SQL level 1
ORA-20001: User EPAY_USER is not allowed to connect from 192.168.219.21
ORA-06512: at line 10

2) log on from the allowed IP address (192.168.219.22) and the connection is successful.
Copy codeThe Code is as follows:
[Oracle @ lxdb1 ~] $ Sqlplus epay_user
SQL * Plus: Release 11.2.0.3.0 Production on Wed Jul 3 11:24:25 2013
Copyright (c) 1982,201 1, Oracle. All rights reserved.
Enter password:
Connected:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0-64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

3) login from the Local Machine (192.168.219.23) is not affected by IP restrictions, and the connection is successful.
Copy codeThe Code is as follows:
[Oracle @ lxdb1 ~] $ Sqlplus epay_user
SQL * Plus: Release 11.2.0.3.0 Production on Wed Jul 3 11:24:25 2013
Copyright (c) 1982,201 1, Oracle. All rights reserved.
Enter password:
Connected:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0-64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options