On Mon, Aug 21, 2017 at 01:38:00AM +1200, Daniel Reurich wrote:
> We discussed a few weeks back in a dev meeting whether or not to revert
> to jessie like naming scheme for ethernet interfaces by default.
>
> The eudev package (currently found in the experimental repos and at
> https://git.devuan.org/devuan-packages/eudev ) utilizes the same logic
> like udev does when it comes to interface naming schemes. The patch
> appended below would reverse the logic and make it opt-in rather than
> opt-out.
>
> This would lead network interface names default to the old "eth0" or
> "wlan0" scheme, rather than the new(?) "enp0s3"-like scheme. It implies
> having "net.ifnames=1" in the kernel cmdline to get the "enp0s3"-like
> scheme and not touching anything to get the "eth0" scheme.
>
> To keep these things consistent we should also apply the same patch to
> udev as well.
>
> Thoughts??

There was a lengthy thread on debian-devel recently. While it did include
the usual shout-fest, there's also a good amount of actually relevant info,
thus I'd recommend reading it.

It starts at:
https://lists.debian.org/debian-devel/2017/07/msg00126.html

TL;DR:

* interface names changing randomly at boot are nasty for machines with
multiple non-bonded interfaces. As drivers are loaded by the kernel in
parallel, they're inherently racey, thus kernel ordering may change.

* any renames to "eth0"/"wlan0" are a losing idea, as a new interface can
appear at any moment, clashing with what you just tried to rename to.
Several approaches to avoid this race have been tried, none worked
reliably. Thus, any sane renaming should use a new namespace. Of what
was proposed, it looks like people liked "en0"/"wl0" the most (yeah, it's
purely an aesthethic thing). My idea "e0"/"w0" is too short to imply
out of context you're talking about interface names, etc.

* systemd-udev's promise of providing _stable_ names didn't deliver. They
still change on major kernel upgrades, and sometimes on every boot.
And their chosen naming is utterly insane (wlxf81a671bcfae, WTF?).
Only systemd proponents still say it's a good idea.

* there's an old alternate solution, package "ifrename" plus a generator,
but that's quite meh

* Guus Sliepen designed and coded a new mechanism and syntax, it's available
in ifupdown in unstable/buster:
.--==[ /etc/network/interfaces ]
rename mac/00:e0:4c:11:7f:4e/=wl0
allow-hotplug wl0
iface wl0 inet static
`----
Would also need a generator.


Thus, I think the best long-term solution would be writing a generation,
using either *udev or ifupdown, that learns new interfaces as they come,
and names them using a single namespace that's not "eth0"/"wlan0".
In particular, a machine with only a single interface (ie, 99% of them)
would predictably have en0 and possibly wl0.

But sticking with just kernel names would still be much better than the
enp0s3 idea. It'd be _predictable_ in that 99% case; machines with multiple
interfaces tend to be either routers (which come preconfigured) or servers
(which have an admin who's supposed to have a clue).

Meow!
-- 
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