The HSRP MAC address has only one variable piece in it. The first 24 bits still identify
the vendor who manufactured the device (the organizationally unique identifier, or OUI).
The next 16 bits in the address tell us that the MAC address is a well-known HSRP MAC
address. Finally, the last 8 bits of the address are the hexadecimal representation of the
HSRP group number.