Sunday, January 02, 2011

Setting the MAC address on an Inspiron 6400

Dell Wireless 1500 802.11n WLAN Mini-card

The card is actually based on a Broadcom BCM4328 chip, and the drivers are from Broadcom. I'm currently using driver version The advanced tab of properties in Device Manager allows a "Locally Administered MAC Address" to be assigned. It is an 8 byte (or 12 character) hexadecimal string using uppercase letters. It must be a locally administered unicast address, meaning the least significant bits of the first byte are 10 (and therefore the second character is 2, 6, A or E). An address which doesn't follow this format will be accepted without any error messages, but the driver will ignore it, and the card will continue to use its original address.

I wonder if the use of a locally administered address is being enforced to prevent copying of other addresses and circumvention of MAC address filtering on wireless networks. I also wonder if it would be easy to reverse-engineer the driver and remove this limitation. However, I currently have no need for this so I will not attempt it.

Broadcom 440x 10/100 Integrated Controller

I'm currently using driver version There was no option for changing the MAC address in the advanced tab of properties in Device Manager. However, the address can be changed via the registry. The registry entry needs to be located within the adapter's numbered key in "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}", the same key where "DriverDesc" is "Broadcom 440x 10/100 Integrated Controller". Its name needs to be "NetworkAddress" and it must be of REG_SZ (string) type. The address must be entered as a hexadecimal number, with uppercase letters and no separators between bytes. After changing this entry, the adapter has to be disabled and re-enabled for it to take effect. (When changing the address via the properties dialog, Windows does this automatically.)

It's possible to add a "Locally Administered MAC Address" item to the advanced properties tab. All the items there are described by keys in the registry in the "Ndi\params" key within the adapter's key. Since the wireless card sets the MAC address in the same way, you can export the wireless card's "NetworkAddress" key, change the adapter number in the .reg file to the 440x, and then import the .reg file. Alternatively, use the following, also making sure that the number ("0007" here) matches the number of the 440x adapter's key:

Windows Registry Editor Version 5.00

"ParamDesc"="Locally Administered MAC Address"

The 440x only demands that you use a unicast address, meaning the least significant bit of the first byte is 0 (and therefore the second character is even). If the bit is not zero, the driver will ignore the address and continue using the original address. Unlike with the wireless card, the locally administered bit does not need to be set. This means the mac address of another device can be cloned or spoofed.

1 comment:

Unknown said...

The MAC address is known from ROM on your network card it is like serial number and cannot be changed without changing the card. New hardware new MAC address but still there are software's which makes it possible.

Silvester Norman

Change Mac Address