Laptop Changing MAC Address

[Bernie Hoefer]

     Hey, all!  Thanks again to Terry and Kyle for helping me at the
February meeting's "general Linux discussion".  I wanted to fill you all
in on what we learned and how it was fixed.



=== Recap Of The Issue ===
     I installed Fedora Linux 25 on a new laptop.  It contained this
wireless network interface:


# lspci | grep "Network controller"
02:00.0 Network controller: Intel Corporation Centrino Advanced-N 6205
[Taylor Peak] (rev 34)


     I discovered the wireless network interface was changing its MAC
address every few minutes.  These entries would appear in the log when
this happened:

NetworkManager[1089]: <info>  [1485323127.6082] device (wlp2s0):
set-hw-addr: set MAC address to 42:5A:67:F8:C7:F9 (scanning)

kernel: iwlwifi 0000:02:00.0: L1 Enabled - LTR Disabled

kernel: iwlwifi 0000:02:00.0: L1 Enabled - LTR Disabled

kernel: iwlwifi 0000:02:00.0: Radio type=0x1-0x2-0x0

kernel: iwlwifi 0000:02:00.0: L1 Enabled - LTR Disabled

kernel: iwlwifi 0000:02:00.0: L1 Enabled - LTR Disabled

kernel: iwlwifi 0000:02:00.0: Radio type=0x1-0x2-0x0

kernel: IPv6: ADDRCONF(NETDEV_UP): wlp2s0: link is not ready

NetworkManager[1089]: <info>  [1485323127.9940] device (wlp2s0):
supplicant interface state: inactive -> disabled

NetworkManager[1089]: <info>  [1485323127.9946] device (wlp2s0):
supplicant interface state: disabled -> inactive

wpa_supplicant[1219]: wlp2s0: Reject scan trigger since one is already
pending

     This made it impossible to join a wireless network that performed
MAC address filtering.  Since this network interface required an Intel
firmware to work, I figured something was broken with that; that it was
getting reloaded over and over again, changing the MAC address each time.



=== Cause And Solution ===
     It turns out, it wasn't a problem -- it was just a new `feature`!
A new privacy feature was added to NetworkManager 1.2, and I had only
used older versions, before Fedora 25.  (Fedora 25 comes with version
1.4.2.)  This privacy feature can be read about here:

<https://blogs.gnome.org/lkundrak/2016/01/18/networkmanger-and-tracking-protection-in-wi-fi-networks/>

(Be sure to also check out the 2016/08/30 update the author puts at the
end of his post, linking to another blogger's posting.)
     The fix was to simply white-list a MAC address in the filter, then
put that same MAC address in NetworkManager's “Cloned MAC address”
field.  I used the nm-connection-editor graphical utility when doing
this, but it can also be done via the command line.  Below is the output
showing the entry, once set:


$ nmcli connection show ExampleWirelessNetworkSSID | grep cloned
802-11-wireless.cloned-mac-address:     AA:BB:CC:DD:EE:FF


     Thanks again to Terry and Kyle (and others who chipped in
suggestions) at the meeting!

-- 
Bernie Hoefer
PGP e-mail is welcome!  Get my 1024 bit signature key from:
<http://pgpkeys.mit.edu/pks/lookup?op=get&search=0x446A6F93>.
"The more I know, the more I realize how much I do not understand."

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