How to implement restrict password with OpenLDAP ?

[yyghp]

I can use "pam_cracklib.so" to limit password ( such as mixing letters with numbers, not dictionary words... ) if I use /etc/passwd ( or /etc/shadow ) to store the passwords, when I use "passwd" to change the password, such PAM module will verify the password automatically...
But if I want to use LDAP to centralize passwords, I have to use ldappasswd to change user password instead of "passwd", then it can even accept any kind of password, like "123" (simple numbers)...
So, how can I restrict password with OpenLDAP ?
Thanks!