[Oracle] 如何使用触发器实现IP限制用户登录

下面是一个触发器的例子：

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;
/

该触发器对用户epay_user进行了ip限制（只允许'192.168.219.20','192.168.219.22'，如果需要设置ip段，用%或?代替即可，如'192.168.219.%‘）。
下面看几个例子测试一下：
1）从非允许ip地址登陆 （192.168.219.21），连接失败

[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）从允许ip地址登陆（192.168.219.22），连接成功

[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）从本地登陆(192.168.219.23）不受ip限制影响，连接成功

[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