On 02/25/2017 10:18 PM, Bill Maidment wrote:
> Hi again
Greetings!

> I have recently rebooted KVM guests with two virtual NICs (e.g. /dev/ens4 and /dev/eth0) only to find that the device name of the eth0 changes to eth1 and so the ifcfg-eth0 doesn't match.
> So I fix the ifcfg file and restart network - all OK.
> On a later reboot eth1 changes back to eth0.
> What is going on? Anyone else observe this phenomena?

Yes. It is part of the goofy new naming structure. It's nice when it
works, but it seems to not-work more often then it does-work. Then it is
infuriating.
<Insert your preferred choice of systemd-udev anger rant here>

Anyway...

Here's the short version.
en: ethernet prefix
o: onboard
s: slot
p: physical location of connector.

If the device is "unknown" then it gets "eth". And of course the numbers
increment for each new device.

So what your device names tell me is that you have one card in slot 4
and a second card that the OS can't figure out where it goes.

There are two ways of "fixing" this.
1)
*If* you have your HWADDR= assigned in your
/etc/sysconfig/network-scripts/ifcfg-eth0 then it *should* always get
that interface regardless of what the OS detects it to be on boot. I
have found this isn't always the case with some specialty cards that
take FOREVER to initialize. I tend to throw in the UUID as well and that
seems to resolve the problems for those cards.

2)
Now, here is the odd part because this next problem is also on my big
KVM host. None of the above worked. I never found a good answer to why
and I am wondering if it is related to KVM...but at this point my sample
size is two so probably not something to make a solid educated guess on...

Anyway..

Read this:
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Networking_Guide/ch-Consistent_Network_Device_Naming.html

There are some good tips throughout chapter 8 on how to tweak and/or
disable udev from scanning devices. I had to rewrite the udev rules on
my KVM box right after 7.1 released because *every* *single* reboot
broke my networking. However, after I adjusted the udev rules based on
the RH documentation I haven't had a problem with reboots since.

I _really_ hope that #1 fixes your issues as it is by far the easiest to
do and manage. If not, the udev rules should do the trick.

One last thought. In that documentation there is something called
"biosdevname"; I'm pretty sure that wasn't in the docs when I was having
a problem with 7.1 as I don't recall seeing it before, but it looks
interesting. You might just want to go through that chapter and give
those suggestions a go.

Hope that helps!

~Stack~