LDAP 操作错误

I have a problem with ldap connection.

$hostname="ldap://sub.domain.com";
$ds=ldap_connect($hostname, 389);
ldap_set_option ($ds, LDAP_OPT_REFERRALS, 0) or die('Unable to set LDAP opt referrals');
ldap_set_option($ds, LDAP_OPT_PROTOCOL_VERSION, 3) or die('Unable to set LDAP protocol version');

if ($ds)
{
$dn = "OU=Users,OU=ro,DC=sub,DC=domain,DC=com";

if (!($ldapc=ldap_bind($ds))) { 
    echo "<p>Error:" . ldap_error($ds) . "</p>"; 
    echo "<p>Error number:" . ldap_errno($ds) . "</p>"; 
    echo "<p>Error:" . ldap_err2str(ldap_errno($ds)) . "</p>"; 
    die;
} 

$attributes = array("sn");
$filter = "(sn=*)";
$result = ldap_search($ds, $dn, $filter, $attributes);

echo $result;
$info = ldap_get_entries($ds, $result);
for ($i=0; $i < $info["count"]; $i++) {
    echo $info[$i]["ou"][0];
}
} else {
    echo "<h4>Unable to connect to LDAP server</h4>";
}

ldap_unbind($ds);

ldap 任何匿名连接都有效，因为我在 AD 浏览器中对其进行了测试，一切都很好.在这段代码中，它停在

ldap_search($ds, $dn, $filter, $attributes);