Use an LDAP URI to configure the location of your LDAP server in $ldap_url:

$ldap_url = "ldap://localhost:389";

You can set several URI, so that next server will be tried if the previous is down:

$ldap_url = "ldap://server1 ldap://server2";

To use SSL, set ldaps in the URI:

$ldap_url = "ldaps://localhost";

To use StartTLS, set true in $ldap_starttls:

$ldap_starttls = true;