How can i access LDAP URI of ldap_search() results in routing script?

I need to do recursive search in company directory within persons that belong to groups, i need to get group id without storing groupid as person attribute, but as an element of resulting URL.
Query base name: dc=example,dc=com.
Query result is cn=user1,ou=group1,dc=example,dc=com.
I can easily get user1 attributes, but how to get ou?