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I've been testing the cloned MAC address feature of Network Manager on a wireless connection and found out something odd: some particular addresses, such as 00:00:00:00:00:00 and 11:11:11:11:11:11, won't work and the MAC address will default to the permanent one.

Thought this might have something to do with the addresses being unrealistic, but addresses like 22:22:22:22:22:22 or aa:aa:aa:aa:aa:aa work perfectly fine, despite not being associated with any known vendor (according to macchanger -l and macvendorlookup.com).

Is this a bug or is there any particular reason for some MAC addresses not to be accepted?

The command I'm using to change MAC address is

nmcli connection modify [connection name] 802-11-wireless.cloned-mac-address [desired mac address]

To apply the change, I do

nmcli connection down [connection name]
nmcli connection up [connection name]

then, to verify the MAC address has changed,

macchanger -s [interface name]

I get the same behavior when I do all this via GUI and on a wired connection.

doctypeme
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2 Answers2

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I enquired with GNOME Bugzilla. Here’s their informative response:

"The kernel doesn't allow assigning a 00:00:00:00:00:00 MAC as it's invalid. Also, MAC addresses with the least-significant bit of the first octet set to 1 are multicast addresses, so they can't be used either"

the second part meaning that all MAC addresses in the following forms are multicast and therefore unassignable:

  • x1:xx:xx:xx:xx:xx
  • x3:xx:xx:xx:xx:xx
  • x5:xx:xx:xx:xx:xx
  • x7:xx:xx:xx:xx:xx
  • x9:xx:xx:xx:xx:xx
  • xb:xx:xx:xx:xx:xx
  • xd:xx:xx:xx:xx:xx
  • xf:xx:xx:xx:xx:xx

The Wikipedia page on multicast addresses also mentions this.

doctypeme
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Could you check if you have other device with the same mac address ? Also you can add any Mac Address even if it's not belong to any manufacture.

Aside note: 00:00:00:00:00 is for Xerox 11:11:11:11:11 is a Private

Samy Massoud
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  • I had checked and no, there's no address conflict with other interfaces. I also found out that 00:00:00:00:00:00 belongs to Xerox and this confirms the problem has nothing to do with the "forbidden" MACs not belonging to a known manufacturer. But then what causes it? I'm extremely curious to know if the issue is specific to my machine or if it's more general. – doctypeme Jun 03 '16 at 14:59
  • Actually I'd forgotten to check the loopback interface, which had indeed the address 00:00:00:00:00:00. But I definitely have no interfaces with address 11:11:11:11:11:11, so address conflict is not the answer. To be sure, I changed the MAC of the loopback interface: even after doing so, I couldn't assign the address 00:00:00:00:00:00 to my wireless/ethernet interfaces. – doctypeme Jun 03 '16 at 15:56
  • sudo ifconfig enp1s0 hw ether 11:11:11:11:11:11 gives me an error SIOCSIFHWADDR: Cannot assign requested address too. Seems @doctypeme is right as the multicast addresses he lists don't work but others appear to. – pbhj Nov 10 '16 at 23:43