Este link explica os endereços MAC: link Do link:
HFC = Hybrid Fibre-Coax. This abbreviation refers to the port of the cable modem that connects to the CATV coax cable. Some cable ISPs require you to register with them the HFC MAC address of your cable modem.
Cable modems might have multiple MAC addresses, one for the HFC side (cable TV coax socket), and one for the CPE side (Customer Premises Equipment, the ethernet socket). USB-capable cable modems also have two further MAC addresses: one for the cable modem USB socket, and another for the emulated network interface in the USB driver in the PC. Although it is possible to discover the CPE MAC address(es) of the cable modem, there is no application or procedure that requires them.
Não tenho certeza sobre por que existem 2 S / Ns. Imagino que um significa algo para uma empresa de cabo, enquanto o outro significa algo para a Motorola.