The interface's physical address. For example, for
an IPv6 interface attached to an 802.x link, this
object normally contains a MAC address. Note that
in some cases this address may differ from the
address of the interface's protocol sub-layer. The
interface's media-specific MIB must define the bit
and byte ordering and the format of the value of
this object. For interfaces which do not have such
an address (e.g., a serial line), this object should
contain an octet string of zero length.
This object is obsoleted by IF-MIB::ifPhysAddress.