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Today I setup a Pi 3B+ with the latest Raspbian Stretch image and recognized a strange behavior:

When initially looking at the network interfaces, the unpredictable network-interface naming was working as expected. My network-interface-names were lo, eth0 and wlan0. This is what I was expecting, as per default /etc/systemd/network/99-default.link is a symlink to /dev/null and thereby prevents the machine to use predictable interface names.

Then I full-disc encrypted the SD-card. More or less, I followed robpol86's really good tutorial on encrypting a Pi (see here: https://robpol86.com/raspberry_pi_luks.html).

Afterwards a strange behavior appeared: My eth0 interface now used a predictable name enxb827...

How is this possible, as /etc/systemd/network/99-default.link is still existing? Also I additionally tried to force the old behavior by adding net.ifnames=0 to /boot/cmdline.txt (and of course rebooting afterwards) but still without success.

I know that there is still another way to solve the problem which is for example given by this answer but I would prefer one of the previous ways, as giving one kernel flag or creating one symlink for me seems cleaner and more fault-tolerant in comparison to editing systemd-files.

Can someone explain to me why the first two solutions do not work anymore after I encrypted my system? Or is there a better way to enforce the old interface-naming? I do not want to use the new interface-names, as e.g. I have iptables rules which I want to use on multiple Pis without editing/templating them each time.

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