Bug#818978: New issues with bridges in Debian Jessie/Stretch

[Michael Biebl]

Am 28.02.2017 um 16:02 schrieb Maciej Delmanowski:
> On Feb 28, Michael Biebl wrote:
>>>>     allow-hotplug br0
>>>
>>> Using allow-hotplug for bridge interfaces is not a good idea. You really
>>> should use that for physical hardware only, which actually is "plugged in".
>>>
>>> If you want to treat it like hotplugged hardware, you have to create the
>>> interfaces yourself (using brctl), as you already noted.
>>>
>>> So, this is really a misconfiguration imho.
>>>
>>> Use "auto br0" and you should be fine.
> 
> Unfortunately, using ifupdown auto/hotplug configuration complicates things
> when 'systemd' is introduced. To summarize explanation found in
> 
> https://lists.debian.org/debian-user/2015/04/msg01208.html:
> 
> The 'auto <interface>' stanza is used by the 'networking.service' which starts
> network interfaces on boot. All of the network interface processes, like
> 'dhclient', started this way end up in one 'networking.service' CGroup. The
> downside of this is that modifications to interface layout need to stop and
> start all of the network interfaces at once, using 'networking.service'. This
> might not apply anymore on Debian Stretch, but it still applies in Debian
> Jessie.

You can still use "ifdown br0" and "ifup br0" if this an auto interface.
But I get your point, that then the resulting processes are no longer
part of networking.service or a specific cgroup which can be used to
reliably kill all process started by ifup.

I think, one solution for this would be, if ifupdown would use
ifup at .service for auto interfaces as well, and networking.service would
simply become a wrapper/dummy service/target which simply triggers the
start of all auto interfaces as instances of ifup at .service.

This is something for stretch+1 though.

The behaviour of ifupdown in stretch is basically the same as in jessie.


Fwiw, the relevant change is
https://anonscm.debian.org/cgit/pkg-systemd/systemd.git/commit/?h=jessie&id=0092dd053b9a830f419dc3d52db09628875275c0

specifically After=sys-subsystem-net-devices-%i.device which means the
ifup at .service instance needs to be started after the device has been
created.

You already found that out yourself and Guus also confirmed it, that if
you use allow-hotplug, you need to make sure that the device is created
by something else

-- 
Why is it that all of the instruments seeking intelligent life in the
universe are pointed away from Earth?

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