What is MAC address?

- MAC stands for Media Access Control; it might not make any sense to anyone, but it actually is sort of serial number for every NIC. That makes more sense this way, doesn't it? MAC is 48 bits long; first 24-bit is to identify manufacturer. For instance, 00:A0:C9:1E:3E:CD is NIC from intel because 00:A0:C9 is OID--Object Identifier--indicated as "intel corporation."

Why do we have to change MAC address?

- There are numbers of reasons why we have to change MAC, but most of the time, we have to change to hide something or pretend to be different called MAC spoofing. For example, we have been blocked by school's network because we don't remember user and/or password or we suck too much bandwidth--torrent?. Then they blocked us! The easiest way to get away is to change MAC--it's like changing a badge :-P so, the system will recognize us as someone else. Or we are sniffing something and we don't want anyone to recognize us.

How to change it then?

- Basically MAC is stored in ROM of each NIC, the only way to change that is to re-write on ROM with different number. However, the procedure to ask for MAC address is depending on OS, so why do we have to change physical stuff while software is much easier to change, right? Thus, it's all up to each OS.

For Linux,

Well, Linux is powerful of tweaking thing as usual. Therefore, it doesn't need anything else rather the utilities it already has.

ifconfig eth0 down
ifconfig eth0 hw ether 00:A0:C9:00:00:01
ifconfig eth0 up

First command is to disable eth0. Then change the MAC address to 00:A0:C9:00:00:01 and bring it up. That's pretty easy, isn't it?

For BSD,

ifconfig xl0 down
ifconfig xl0 link 00:00:00:AA:AA:AA
ifconfig xl0 up

It's working pretty much the same as Linux =)

For Windows,

MAC can be changed two ways: editing Registry directly or using Windows itself or 3rd party software. For editing Registry, you have to find in

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\

Then you will find a bunch of folders (0000, 0001, 0002, ...) You just have to go through everyone until you find NIC you want to change. After that, you will have to add "String entry" named "NetworkAddress" which has value as MAC you want such as 000475123456, no colon or anything between numbers. Then restart once or disable and enable that NIC. It will be all set.

NetworkAddress - Registry Editor
NetworkAddress - Registry Editor

Another way is using 3rd party software. There are tons of software available to do this such as Mac Makeup or MadMACs. Mac Makeup is for changing MAC pretty easy while MadMACs will random MAC address and/or hostname.

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