[Oracle] How to Restrict User Login with IP Using Triggers

Here is an example of a trigger:

create or replace trigger logon_ip_control
after logon on 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;
/

The trigger imposes an IP restriction on user EPAY_USER (only '192.168. 219.20', '192.168. 219.22' are allowed, and if you need to set IP segment, you can replace it with% or?, such as' 192.168. 219.% ').
Here are a few examples of Test 1:
1) Log in from a non-IP address (192.168. 219.21) and the connection failed

[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, 2011, 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 in from the IP address (192.168. 219.22) and the connection is successful

[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, 2011, Oracle.  All rights reserved.
Enter password: 
Connected to:
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 local (192.168. 219.23) is not affected by IP restriction, and the connection is successful

[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, 2011, Oracle.  All rights reserved.
Enter password: 
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options