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;
/

[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

[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

[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