Unique identifier indicating a black list switch. Value format of the
this object is 'XXXXYYYYYY', in which 'XXXX' is reserved as 4 bytes
of 0x0, 'YYYYYY' is a MAC address.
For example, if the MAC is 000f-e459-000a, the value of this object is
an octet string: '00' '00' '00' '00' '00' '0f' 'e4' '59' '00' '0a'.