MAC stands for Media Access Control. It’s an important element of computer networking. MAC address helps to identify the computer on LAN and this is an important component for different protocols.

Many internet service providers use to ask about the MAC address of users device so that they can allow the internet services for that specific address. If the user changes the network card or installs any new router then the new address would not work for you to get the same services from your service provider. But different machines use to allow modification or spoofing in this address.

Most of the time MAC address is changed because of some security issues. MAC addresses are 12-digit hexadecimal numbers (48 bits in length).

Changing the MAC address on Linux: Following are the commands to change the MAC address on Linux:

ifconfig eth0 down hw ether 00:00:00:00:00:01
ifconfig eth0 up

These two commands will let the user set the eth0 interface to use the MAC 00:00:00:00:00:01. Users just have to enter the new NIC that they want to use further with the MAC address into the commands. It’s much easier to change the address on Linux than Windows.

Changing the MAC address on Mac OS X:
Under Mac OS X, address can be changed by following the same method as was followed in Linux. Use any of the given commands to change the MAC address:
sudo ifconfig en0 lladdr 00:01:02:03:04:05
Or
sudo ifconfig en0 ether 00:01:02:03:04:05

These two commands use to work for computer Ethernet card only. These spoofing methods work for AirPort Extreme (2.0) cards only. With the help of SpoofMac AirPort Extreme MAC address can be changed.

Changing the MAC address on Windows 2000/XP/Vista:
In Windows 2000/XP/Vista, the MAC address can be changed by altering the Ethernet adapter’s Properties menu, in the “Advanced” tab as "MAC Address", "Locally Administered Address", "Ethernet Address" or "Network Address". Name that your system would be using depends on the Ethernet driver that you are using.

Beside this in Windows you can use the “reg” command to edit the address form the console. All the information about your current NICs can be found on register key
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\.

Using this key you can find all of the sub keys and settings for each network interface. All the content that you will find here is known as Network Address, and this will be used to alter the MAC address on the adapter. To find the correct key out of many we can search for the value "DriverDesc" until the desired NIC is found. Once you set the "Network Address" then you just have to disable and then enable the NIC, so that it can start working. To confirm the new MAC address you can run "getmac" or "ipconfig /all" commands.

Changing the MAC Address on Router:
Different routers use different method to change the MAC address. All the routers cannot change their MAC address as well. During the alteration process of MAC address routers use the CLONE MAC Address. This method is known as CLONING. This is a quick and better way to change the MAC address without the hassle of disabled internet connection. Under this method MAC address needs to be changed to new device which can match the address of original device. The actual physical address cannot be changed in the hardware but with the help of software that address can be emulated. Many broadband routers now days support this cloning method. The emulated address use to appear to the ISP as the original hardware address. Procedures of cloning can differ according the type of routers.