Under Windows 7, the possible range of spoofed addresses for wireless adapters that can be set is limited. To be used by Windows 7, a spoofed MAC address should have 0 as a least significant bit (unicast) and 1 as a second least significant bit (locally administered) in the second nibble. Thus possible values for the second nibble are limited to 2, 6, A and E.
In other words
MAC address: “XY-XX-XX-XX-XX-XX” “X” can be anything hexadecimal. The hexadecimal “Y”, written in binary format, is Y: “kmnp”, where “p” is the least significant bit;
p=0 --> unicast;
p=1 --> multicast;
n=0 --> globally assigned MAC;
n=1 --> locally administered;
So, actually MAC can be changed to any combination in which p=0 and n=1;
“Y” can be 2, 6, A or E.
So the possible MAC addresses in Windows 7 for wireless adapters:
- X2-XX-XX-XX-XX-XX
- X6-XX-XX-XX-XX-XX
- XA-XX-XX-XX-XX-XX
- XE-XX-XX-XX-XX-XX
It is limitation from Microsoft.
Sometimes the problem can be fixed by downgrading driver for wireless adapter and installing its version for Windows XP. And then the MAC address can be changed to any MAC address without limitation. But downgrade may cause incorrect work of device.
Additional information about changing MAC address - Tutorial "Changing MAC address in Windows 7".
