Network Protocol: Mac Address

Mac Addresses – Data Layer

Each physical network interface card (NIC) has a unique identifer assigned to that NIC.   This unique identifier is called a Mac Address.  A mac address contains a vendor ID and a serial number and is made up of 12 hexidecimal characters.  Mac addresses are part of the Data layer of the OSI model and used heavily in Ethernet node to node transmissions.  Each nic responds to two addresses; it’s own unique address and the broadcast address of ff:ff:ff:ff:ff:ff.   In linux you can display your MAC address by using the command ifconfig -a.  It will display something similar to this:

ifconfig -a
eth0      Link encap:Ethernet  HWaddr 00:0E:A6:7A:19:E1
inet addr:  Bcast:  Mask:
inet6 addr: fe80::20e:a6ff:fe7a:19e1/64 Scope:Link
RX packets:42708883 errors:0 dropped:0 overruns:0 frame:0
TX packets:167206053 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3679921735 (3509.4 Mb)  TX bytes:879524352 (838.7 Mb)
Interrupt:201 Base address:0xe000

The HWaddr is the current mac address.  Most modern NIC’s support MAC address spoofing this can be done in almost any operating system.  Since mac addresses can be spoofed quickly it is not a good method for secure authentication of machines.  A lot of wireless routers use mac addresses as a method of access control this alone should not be the method of access control.    In Linux ifconfig allows you to change your mac address.  For example:

ifconfig hw ether 00:01:02:72:45:C2

Would allow me to change my mac address to 00:01:02:72:45:C2.

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