Captive Portal Allowed MAC Address

[behcs]

In the Zone Edit Dialog, we can enter "pass thru" IP or MAC in the following field.
Allowed addresses -- this is for IP addresses or subnets
Allowed MAC addresses -- this is for MAC addresses

My question is, how OPNsense control the allowed MAC Address? When I run "ipfw list", I don't see any rules associated with the MAC address that I enter in "Allowed MAC address".

Is there any other means for me to verify this?

thanks!