[Gllug] Fedora 16 MAC Address

[Nix]

On 16 Apr 2012, Mick Farmer said:

> Dear GLLUGers,
>
> I'm running on a Dell Inspiron N5030.
> 
That doesn't tell us what network card you've got. lsmod would be more
useful. A little googling suggests it may be an Atheros AR8151.

> eth0      Link encap:Ethernet  HWaddr 8E:30:4D:34:6F:DE  

One MAC address...

> eth0      Link encap:Ethernet  HWaddr 9E:8F:2E:02:71:B7  

... another MAC address. The MAC has changed, and changed drastically
(even the manufacturer OUI in the first three fields has changed).
This is going to be problematic.

Obviously, neither of these addresses appear in the OUI database.
Even more disturbingly, while the first address is a valid locally
administered address, the second is not (unless I messed up my
hex-to-binary conversion). Something is very wrong here.

The Atheros AR8151 appears to be driven by atl1c.ko.

If this driver cannot get a valid MAC address off the card's EEPROM, it
grabs a random one using random_ether_addr(), which always sets the
locally administered address bit. (Before v2.6.36 the driver did not do
this, but this is redundant because F16 definitely uses a later kernel
than that). It also sets a bit to indicate that this address was
randomly assigned. If this was so, you should find that
'cat /sys/class/net/{interface name}/addr_assign_type' prints '1'
(whereas for permanent hardware addresses it would print '0').

Another possibility is that the MAC on your device is being correctly
set, but something in the boot scripts is overwriting it before the
machine finishes booting (which Linux allows if you're running as root).
I don't know of a way to diagnose this case. (I also don't know of a way
to diagnose the case that the EEPROM is simply buggy, and I don't have
the hardware spec sheets so I can't tell if the driver is looking in the
right place in the EEPROM for the MAC address.)

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