Raspberry Pi MAC Address Changing on Reboot

I recently did a apt-get dist-upgrade on my Raspberry Pi running Raspbian 8 and when I rebooted the device appeared to drop clean off my network. I was away from home at the time so I decided to fix it when I was next on the premises – it wasn’t a hugely important device to have running 24/7.

When I looked at the device in person I realised that it was in fact connected to the network, but with a different IP address to that it had held before. Having MAC address based IP allocation, this seemed rather strange. Looking at the MAC address in ifconfig revealed the problem – it had changed! Thinking this to just be a fluke, I rebooted. Now, not only was the MAC still different to that which it should have been, it had changed a third time!

Investigating what had happened during the upgrade revealed that both the bootloader and the kernel had both been upgraded, but for whatever reason, the new kernel wasn’t being loaded. Modifying the /boot/config.txt as follows along with a reboot fixed this discrepancy and lo and behold the MAC returned to it’s former value and the device picked up the IP address it was supposed to have over DHCP

From

[pi1]
kernel=vmlinuz-4.4.0-1-rpi
initramfs initrd.img-4.4.0-1-rpi followkernel
# to enable DeviceTree, comment out the next line
device_tree=

To

[pi1]
kernel=vmlinuz-4.9.0-2-rpi
initramfs initrd.img-4.9.0-2-rpi followkernel
# to enable DeviceTree, comment out the next line
device_tree=

It’s worth pointing out that you may have a similar problem with a similar cause but slightly different kernel versions to me. If this is the case, or to check if it is, verify the old/new versions in /boot as follows

ls -lha /boot | grep initrd.*rpi

Which will reveal your old/new versions

-rwxr-xr-x 1 root root 5.7M Jul 3 18:26 initrd.img-4.4.0-1-rpi
-rwxr-xr-x 1 root root 13M Jul 3 18:46 initrd.img-4.9.0-2-rpi

You should then modify /boot/config.txt from the old version to the new version as per my above example.

   

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