Hardware identifier. see wikipedia topic MAC address
Media access control ID
MAC-48 - original 48 bit hardware identifier.
EUI-48 - newer protocol, essentially the same but can be used with
virtual devices.
EUI-64 - 64 version.
Compatible with IPv6
Provides tweaks so MAC/EUI-48 can be easily converted to valid EUI-48 and back.
Structure of ID
24 bit OUI - Organizationally Unique Identifier
Assigned by IEEE to specific manufacturers.
Some manufacturers may have multiple Ids.
1 bit reserved to flag uni-cast/multicast
1 bit reserved to flag local/global administration of OUI.
24 bit NIC - Network Interface Controller Id.
Manufacturer's unique ID for device.
All networked communication done via network frames.
Frames contain a source and a destination Mac Id and a payload.
Frames can only move between nodes a local network following specific
protocol.
To uniformly communicate between any node on the 'Internet', a virtual
connection protocol called TCP/IP provides for a device independent address.
Payloads consist of packets of information usually following the TCP/IP
protocol which include source and destination IP addresses that are valid
across all networks.
Frames not targeted for a local node must pass through a gateway node
which will strip the current frame off and encapsulate in a frame appropriate
to the protocol of the network hop.
Services, DHCP, bootp, arp/rarp exist to convert between MAC Id and
IP@.
The DHCP service will identify when a packet is targeted to a local system
or target the gateway in the appropriate manor to pass packet on to next node
hop.
On Linux systems, use arp to display recently discovered MAC addresses.