This is covered in Chapter 13.

1. IEEE MAC Addressing
   1. 48-bit address for devices attached to a LAN.
   2. Assigned address: high bit is zero.
      1. Confusingly, this means the low-order bit of the high-order byte. (It's the first bit to arrive in Ethernet byte order.)
      2. This is a fixed address assigned to the hardware at manufacture.
         1. The high 24 bits is an Organizationally Unique ID (OUI), assigned to the manufacturer by IEEE.
         2. The low half makes the address unique.
         3. Despite “fixed,” many net devices, including most wireless ones, allow the assigned MAC to be replaced with an arbitrary one.
            1. MAC address spoofing.
            2. Privacy or hacking, depending on your point of view.
            3. Some OS's use this to generate random MAC addresses for privacy.
            4. But might keep your device from being assigned an IP address.
   3. Broadcast address: FF:FF:FF:FF:FF:FF.
      1. Obviously, the high bit is not zero.
      2. This packet is addressed to all stations on the LAN.
      3. But administrators may limit their propagation
   4. Multicast: High bit is 1, but not the broadcast address.
      1. Addressed to any host configured to receive it.
      2. Allows sending to an arbitrary subset of nodes.
2. Delivery
   1. Originally, all packets were delivered to every node.
   2. The node would decided if it is a recipient, and drop it otherwise.
   3. This has changed LAN-level routing has changed, though nodes still receive (and discard) some packets that are not for them.
   4. Though most receivers are capable of entering “promiscuous mode,” where they receive all packets the net delivers.