MAC Addresses

48 bits long, usually represented as 6 groups of hex (e.g.aa:bb:cc:dd:ee:ff).

Manufacturers 'burn in' a MAC address to each port on a device, however most modern equipment allows the MAC to be changed in software as well.

Organizational Unique Identifier - (OUI) First 3 bytes.

  • OUIs specific to each manufacturer (VMWare OUI 00:50:56, Intel OUIs 00:02:B3, 00:03:47, 00:04:23)
  • Majority of the time OUIs are enforced. The MAC address of a device will be unique within the network
  • LSBit in 1st byte in OUI determines if address is unicast (0) or muilticast(1)
  • 2ndLSBit in 1st byte in OUI determines if the mac is globally unique (0), or locally administered (1)

Host ID - Last 3 bytes

  • Randomly decided by manufacturer
  • Ideally there are no collisions within a physical network

Special MAC Addresses

  • The Layer 2 BROADCAST address for IPv4 and ARP is FF:FF:FF:FF:FF:FF
  • The Layer 2 MULTICAST address for IPv6 is 33:33:00:00:00:01

results matching ""

    No results matching ""