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I would like my MAC addresses on my Mac OS X (iMac) and iOS devices (iPhone, iPad) to be randomized on boot. I have no idea how to generate the random MAC, nor to insert it into the boot process. Any help would be greatly appreciated!

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What are you attempting to achieve by this? Knowing your objectives would help in finding a workable solution. –  Michael Kohne Sep 16 '10 at 11:25

5 Answers 5

You can't. The Ethernet and AirPort (Wi-Fi) drivers in Mac OS X don't reliably support changing your MAC address. I suspect the same is true of iOS, although I haven't tried it on a jailbroken iOS device.

Was this about privacy, or something else?

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I guess "each device will have 30 minutes free wifi" –  celeron533 Dec 17 '14 at 2:48
sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -z
sudo ifconfig en1 ether 00:11:22:33:44:55
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Besides questioning why, and thinking that this will be more work than will probably benefit you, realize that a truly random MAC will cause problems.

The main problem I see is grabbing by accident the same MAC as someone on the network you're on, or will later join. Also, part of the MAC is a hardware manufacturer identifier, so a truly 'random' MAC would possibly cause problems.

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Given the number of possible MAC addresses (281 trillion) causing a collision seems fairly improbable. –  Dracs Feb 26 '12 at 5:29

To change the MAC address of a jailbroken iOS device (one-time, not quite on-every-boot):

  1. Generate a MAC address. openssl rand -hex 6 should work.

  2. Ensure that the MAC address is unicast and "locally administered", which means the second digit must be one of 2, 6, A or E (x2:xx:xx:xx:xx:xx). This will prevent weird things from happening.

  3. On a rooted iOS device, run:

    su -
    nvram wifiaddr=4a:1c:ff:c1:d0:c0
    
  4. Reboot the device.

  5. After reboot, my iOS device reported that the iTunes library was corrupted, and was unable to sync with iTunes. Remove these files, and the device should regenerate the iTunes library from the media on disk (please be careful):

    cd /var/mobile/Media/iTunes_Control/iTunes
    mv iTunesCDB iTunesCDB-backup
    mv iTunesControl iTunesControl-backup
    mv iTunesPrefs iTunesPrefs-backup
    
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Um, the mac address is the physical address of your network device. It is set by the manufacturer and cannot be changed. At least not with software. With some h/w hackery, you probably could.

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Not true. Although you're correct that the MAC address was originally intended to be permanent, most modern network cards are more than capable of having their MAC address changed with software. See en.wikipedia.org/wiki/MAC_spoofing for some simple examples of how. –  Scott Sep 16 '10 at 9:46

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