LDAP proxy with back_ldap: (?=undefined)

Hi all!

I am trying to setup the simplest possible LDAP proxy with OpenLDAP. Actually, I do have a machine with one interface on a public IP address and the other one on the private network. So all I want is a pass-through of any LDAP query 1:1 from the proxy which sits on the public IP to an LDAP server which can be reached only through a private IP on our internal network.

Here is my config:

database ldap suffix "o=top" uri "ldap://192.168.12.34/"

My problem is: The query sent to the backend server always contains a (?=undefined) condition, which leads to no objects found.

In other words, the query I send to the proxy is for example:

(&(?objectClass=mailalias)(dc=xxxx.yy))

The back_ldap will send to the backend server:

(&(&(?objectClass=mailalias)(dc=xxxx.yy))(?=undefined))

Any idea?

Regards, Torsten