How do you whitelist MAC addresses on the XR500

ACL was removed in the latest firmware, I believe it had some stability issues. MAC address filtering provides no real security, rather like hiding your SSID,  but it does provide a false sense of security in my view. It is so easy to spoof by someone using say kali linux and Wireshark for instance. There are even videos on youtube to show how to do it! You really are better off using something like a 8-16 character ASCII WPA2 password. Also some operating systems use MAC address randomisation, like Apple for instance and MAC filtering can actually make connection to the router more problematic.