Kabel Deutschland HotSpots and WiFi MAC’s

If you happen to be in Berlin, you can get 30 minutes of free WiFi in quite a lot of places from a KabelDeutschland™ HotSpot. Unfortunately, each connecting device gets only 30 minutes of free internet per day. On a completely unrelated note, I will talk about changing the MAC address of your WiFi card in Windows 7. I must, again, emphasize the fact that these two topics are in no way related. # How to change the MAC * Do an ipconfig /all and find the description of your WiFi card's adapter. * Go to HKEY_LOCAL_MACHINE → \SYSTEM → \CurrentControlSet → \Control → \Class → \{4D36E972-E325-11CE-BFC1-08002BE10318} as an administrator and navigate to the subkey whose DriverDesc matches this description. * Change the entry NetworkAddress to the desired MAC address. It's supposed to be a string value of exactly 12 hexadecimal digits, no spaces or dashes. If the key does not exist, simply create it. * Disable and re-enable your network adapter. Alternatively, you can download the MAC Address Changer from CodeProject, which is open source and performs exactly the above procedure, but with a nice GUI. # That all? No. Of course not. I was changing my MAC back and forth and the adapter just kept switching back to the original MAC, until I finally figured out the problem. In Windows 7, if the MAC of a WiFi adapter is of the form XY-XX-XX-XX-XX-XX, then X may be any hexadecimal digit. However, the lower two bits of Y have a special meaning. Write Y=[abcd], i.e. a to d are the binary digits of Y. Then, \[ d = \left\{ \begin{array}{ccl} 0 &;& \text{Unicast} \\ 1 &;& \text{Multicast} \end{array}\right. \qquad c = \left\{ \begin{array}{ccl} 0 &;& \text{globally assigned MAC} \\ 1 &;& \text{locally administered} \end{array}\right. \] We want our adapter to be unicast and locally administered. So we're left with the four choices 2, 6, A and E for Y. # So now that's all? Yea that's all. Enjoy Berlin!