Filtering valid users on LDAP authentication

Hi all!

I look for a similar concern in this forum but without success. Let me make now my question:

Context

My Moodle 2.4 has set up a branch on LDAP server for authentication purposes. Till now, all existing users on that LDAP branch can log in into Moodle.

New need

That LDAP branch now has more users than those that have to have access into Moodle, so that I need to filter out users from LDAP server by a given list of values in a custom attribute.

What should I do to do so without programming anything? I tried something using a filter in the "memberattribute" field but all failed.

Can you provide me any help?

Thanks in advance!

Best,

Jordi