How Debian managed the systemd transition [LWN.net]

How Debian managed the systemd transition

Posted Sep 19, 2015 1:34 UTC (Sat) by dlang (guest, #313)
In reply to: How Debian managed the systemd transition by kreijack
Parent article: How Debian managed the systemd transition

> BTW I never seen a swap of the ethernet cards;

a swap can happen if you have cards that use different drivers and the driver load order changes (either from driver renaming if the drivers are statically linked, or the device discovery order if they are modules)

a swap can also happen if the bus the cards are on does not have an order and orders based on the order devices respond. I'm told that USB can detect the physical location of a device, but asaik, all the drivers ignore this and rely on which device responds first to device probing.

But if the device has a MAC address as part of the device, the existing tools can keep the ordering consistant.

If there is no such identifier built into the card, I don't believe that the new process is really any more reliable.

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How Debian managed the systemd transition

Posted Sep 20, 2015 10:22 UTC (Sun) by kreijack (guest, #43513) [Link] (3 responses)

> a swap can happen if you have cards..
What you are saying is correct.... But I repeat in my (very limited) experience I never seen that.
What I see is that the ethernet name change from eth0 to eth1 when I moved from a disk image from one host to another, and that cause me more headache then the fact that I have more ethernet device of different hardware...

What I mean is that linking the ethernet name to the hardware is useful in some contexts, but in others not; and I suspect that these "others" are more common than the former...

How Debian managed the systemd transition

Posted Sep 20, 2015 10:52 UTC (Sun) by dlang (guest, #313) [Link]

I agree, I always disable that on my systems. But I can see that if someone was dealing with multiple USB interfaces, or wants to do async module loading (with all the ordering race conditions it introduces) in search of faster boot times, I can see why it could be useful.

How Debian managed the systemd transition

Posted Sep 25, 2015 20:16 UTC (Fri) by Wol (subscriber, #4433) [Link] (1 responses)

> What I mean is that linking the ethernet name to the hardware is useful in some contexts

You mean, like in a firewall, for instance ...

I saw a comment somewhere where eth0 and eth1 got swapped. In other words, until someone noticed, the firewall's soft, unprotected, meant for the internal network, interface was the interface to the hostile outside world ...

Cue major panic, lan disconnected from the internet, rebuild the firewall from scratch, ...

At the end of the day, unpredictable behaviour is a security risk. What I think happened was that the system had always been booted from cold, and had always been predictable. Then for some reason, one day it did a warm-start, and came back with the interfaces swapped over ... oops ...

Cheers,
Wol

How Debian managed the systemd transition

Posted Sep 25, 2015 20:36 UTC (Fri) by dlang (guest, #313) [Link]

actually, if the firewall interfaces get swapped, it's not going to talk to anything, because it is going to send the reply packets out the wrong interface (unless you also have dynamic routing)

Yes, it is possible to configure a system so that it's IPs and routes will swap with the interface changes, but the firewall rules won't, but that's getting into rather contrived territory.