MAC stands for Media Access Control which is a six byte number, usually expressed as a twelve digit hexadecimal number. IPs in LAN are translated to MAC address by the ARP (Address Resolution Protocol) protocol. For some reasons such as keeping the true MAC address from being logged, accessing to the network which bounds IPs together with MAC address, the MAC address of NIC card may need to be changed.
Shut down the interface
# ifconfig eth0 down
Changing the MAC address of the interface
# ifconfig eth0 hw ether 00:00:00:00:00:01
Bring up the interface
# ifconfig eth0 up
Checking the new MAC address
$ ifconfig eth0
The MAC address should be changed to 00:00:00:00:00:01 now.