[systemd-devel] Stable interface names even when hardware is added or removed, not true

[Pekka Sarnila]

On 'Predictable Network Interface Names' it states as a benefit of the 
new policy:

   Stable interface names even when hardware is added or removed, i.e.
   no re-enumeration takes place

Unfortunately this is not true.

I'm running a mail server, kernel 4.8.6. Graphics card started to fail. 
Replaced it with new one (newer model). Booted the system.

All seemed to be fine, network seemed to work. But after some time got 
angry cries: 'can't read the mail !!!'. A big headache.

Although the new card was in the same slot as the old one kernel had 
changed the name enp6s0 -> enp3s0 (no firmware/BIOS index available and 
kernel policy was used as default). Since enp6s0 was not found our 
server instead of fixed ip address used our dhcp-server to get a random 
temp address. Thus network worked, but not in the mail-servers correct 
address.

To figure this out took some nervous time.

Now, I don't know why kernel driver got a different name for this 
network interface (ethernet hardware is on the motherboard, and it is 
the only net hardware on the system). But obviously it can happen.

Could there be general solution for this? On ordinary system MAC could 
be used, but on virtual one. And there are of course docking systems for 
laptops. So that is not general enough.

It would seem there is no general way to enumerate persistently network 
interfaces unless the network hardware itself directly gives its name 
(and have unique names over the world). Or is there?

However could there be a way for systemsd/udev to know that there is 
only one interface in the system? At least then always as a default the 
same name could be given.

Pekka