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Acronym for Media Access Control.

This is the LinkLayer?, and is usually talked about in Ethernet where it has a very simple structure:

| from hardware address | to hardware address | protocol field | <data>

The term MAC Address is also used to refer to the hardware address of an Ethernet card. These are usually hard-coded in an Address ROM on the network interface card.

A MAC address is 48 bits long, and is commonly represented as a colon-delimited sequence of 12 hex digits - "". The first 24 bits/6 digits identify the manufacturer of the network card, as overseen by the IEEE and IANA. See for more information.

A MAC address should be globally unique - no two network cards should ever have the same MAC address. Note that some network cards (notably, those used with Solaris machines) may be software-reprogrammable.