create or replace trigger logon_ip_control
after logon on database
declare
  ip STRING();
  user STRING();
begin
SELECT SYS_CONTEXT('USERENV','SESSION_USER') into user from dual;
SELECT SYS_CONTEXT('USERENV','IP_ADDRESS') into ip from dual;
if user='system'
  THEN
      IF ip not in ('127.0.0.1','10.24.200.200')
      THEN raise_application_error(-,'User '||user||' is not allowed to connect from '||ip);
      END IF;
END IF;
end;
/