What is … a MAC-address?

A MAC address is a known term but a tester is not much confronted with it.  MAC stands for Media Access Control and is also known as the physical address.  In fact, it is a unique identifier embedded in the hardware circuitry.  The MAC address enables devices to communicate with each other in a network.

The current MAC addresses (also known as MAC-48) are designated by twelve hexadecimal figures grouped into couples and separated by colons or hyphens.  Therefore, it ranges from 00:00:00:00:00:00 to ff:ff:ff:ff:ff:ff:ff.  As with IP addresses, it is expected to become exhausted.  Although the current standard provides more than 281 trillion possibilities , a new standard is being devised to mend the potential problem of depletion.  As with the new IPv6 addresses, the EUI-64 (the Extended Unique Identifier – 64 bits) is designed to mitigate the exhaustion of the current way of designating MAC addresses.

The current 48 bit MAC address consists of two parts (each sizing 3 bytes or 24 bits):

  1. OUI (Organisationally Unique Identifier) and
  2. NIC (Network Interface Controller).

The OUI is in fact the stamp by which the manufacturer, vendor or other organization of the network appliance can be identified.  The second part makes each device unique worldwide.


Click to enlarge

The differences between a MAC address and an IP address are:

  1. A MAC address uses the datalink layer (also known as layer 2 in the OSI-model) while an IP address uses the network layer (known as layer 3 in the OSI-model) and
  2. A MAC address is in normal use fixed on the hardware appliance while an IP address is temporarily given by the DHCP server or router.

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