Comment 4 for bug 1544747

See https://lists.ubuntu.com/archives/ubuntu-devel/2015-May/038761.html for more details about the change, and /usr/share/doc/udev/README.Debian.gz how the current schema works, and how to set custom names or change the policy, if you desire so.

So the lack of /etc/udev/rules.d/70-persistent-net.rules is intended, unless this was an upgrade from trusty -- in that case the file should of course continue to exist (we don't remove it automatically on upgrades). But it sounds like this was a new install.

So for the most part this all works as intended. The main point of contention is the naming of USB devices ("enx8cae4cff4099") -- see the ML discussion for why this is currently done. I'm fine to change this to a different policy if desired by the server or other teams, but everytime I asked about it I get a resounding silence as an answer :-) Retitling the bug accordingly.

I. e. an alternative policy would be: Always use the kernel names for USB devices. As long as you have only one, it will always be eth0, but as soon as you have multiple ones *and* you need to refer to their names in configuration files, then you need to define a naming policy yourself, as the kernel names are not persistent and predictable.

In theory we could also use the path based names for USB devices, which would name the interface according to the port you plug it into. That'd be a good policy for things like a RasPi where you deploy the same image (with that policy) to lots of devices and port location would make sense. This policy makes less sense on a laptop where you might plug in your mobile phone on different ports every time -- but then again those usually use NetworkManager and dynamic configurations where you don't care about device names.