BSD
1) Bring down the interface: “ifconfig xl0 down”
2) Enter new Mac address: “ifconfig xl0 link 00:00:00:AA:AA:AA”
3) Bring up the interface: “ifconfig xl0 up”
Linux
1) Bring down the interface: “ifconfig eth0 down”
2) Enter new Mac address: “ifconfig eth0 hw ether 00:00:00:AA:AA:AA”
3) Bring up the interface: “ifconfig eth0 up”
Windows 2000/XP
Method 1:
This is depending on the type of Network Interface Card (NIC) you have. If you have a card that doesn’t support Clone MAC address, then you have to go to second method.
a) Go to Start->Settings->Control Panel and double click on Network and Dial-up Connections.
b) Right click on the NIC you want to change the MAC address and click on properties.
c) Under “General” tab, click on the “Configure” button
d) Click on “Advanced” tab
e) Under “Property section”, you should see an item called “Network Address” or “Locally Administered Address”, click on it.
f) On the right side, under “Value”, type in the New MAC address you want to assign to your NIC. Usually this value is entered without the “-” between the MAC address numbers.
g) Goto command prompt and type in “ipconfig /all” or “net config rdr” to verify the changes. If the changes are not materialized, then use the second method.
h) If successful, reboot your system.
Method 2:
This should work on all Windows 2000/XP systems
a) Go to Start -> Run, type “regedt32″ to start registry editor. Do not use “Regedit”.
b) Go to “HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}”. Double click on it to expand the tree. The subkeys are 4-digit numbers, which represent particular network adapters. You should see it starts with 0000, then 0001, 0002, 0003 and so on.
c) Find the interface you want by searching for the proper “DriverDesc” key.
d) Edit, or add, the string key “NetworkAddress” (has the data type “REG_SZ”) to contain the new MAC address.
e) Disable then re-enable the network interface that you changed (or reboot the system).
Method 3:
Use the program Etherchange from http://ntsecurity.nu/toolbox/etherchange/
Windows 9x
Use the same method as Windows 2000/XP except for the registry key location is “HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\Net” and you must reboot your system.