[CrLf]

Network interfaces should not rename themselves after reboots. On Red Hat derived distributions, the device name is tied to the MAC address of the interface, so it never changes.

On other distributions, "udev" accomplishes the same thing.

The only point when interface naming is arbitrary is at installation time, then it stays the same forever.

Not only this will add confusion by introducing a bunch of new names for network interfaces, it will also break applications that rely on them being called "ethX".

It will also make it impossible to manually assign names to interfaces. For instance, if you have a configuration that uses an embedded interface and you want to add another interface on a card, you can manually assign the same "ethX" name to it, but not if the names depend on the physical characteristics of the hardware.

[sciurus]

No, you can still rename interfaces using udev just like you can now. This is largely about ensuring that devices get predictable name at install time. As is pointed out in the LWN comment thread, for anyone who has to provision large number of servers with multiple NICs that connect to different networks this is a godsend.

Ability to rename: http://lists.us.dell.com/pipermail/linux-poweredge/2010-Nove...

Why the eth prefix can't be used: http://lists.us.dell.com/pipermail/linux-desktops/2011-Febru...

More background: http://domsch.com/blog/?p=455

[ay]

Why not give an argument to the kernel to create the new devices as "fooX" (foo being a supplied parameter) - and let udev userland deal with the renaming to "ethY" as it pleases ?

While this novelty certainly may appeal to the folks who are used to alphabet soup in the network adapters list, and I too think that the adapters that distinguish between the T568A and T568B cable layout have a degree of coolness in them by creating an extra value in being able to distinguish between the straight and crossover cables - overall it seems like a step back to me.

I would plug in the interfaces into a switch - and all I care is to find the same MAC address as I see on the switchports - not which bus they attach to.

[rdtsc]

Good point, however, the problem is only half-solved.

If the machine is coldstarted then previous devices could be randomly reshufled. Imagine you have a datacenter with 100 machines and you have some kind of provisioning scheme where you coldstart them often. It would be a nightmare having to run ethtool -p <dev> and replug cables.

We have solved the problem by providing a consistent algorithm of sorting all the devices in a udev callback. We have a known set of hardware so we know which cards are add-ons (our machines have 4+ eth ports) and which ones are built-ins. So it works out, however, it would be nice to generalize it somehow.

[nailer]

> If the machine is coldstarted then previous devices could be randomly reshufled.

The detection order would change, but the ifcfg file (RH) or udev rules (SuSE and others) would not change, so your NICs will stay the same these days.

[rdtsc]

ifcfg file is auto-generated by the coldstart. But you are right, if we save and restore ifcfg files then it would work. However if this saving and restoring has to be done after machine is coldstarted, its eth0 could be connected to another network completely.

[nailer]

The first time the OS boots, the MAC addresses in ifcfg files are generated. Subsequent cold starts only read the files, they do not write them.

[rdtsc]

That is the the problem I am trying to convey -- the machines are coldstarted often and MAC addresses are reshufled on every first boot. If your cable to the management network is connected to left socket on the motherboard, that left socket needs to be eth0 on every coldstart. Sometimes it is not. "Yes" after the first boot when ifcfg files has been written it will be stable, but that mean someone has to go and either hand-edit ifcfg files or run ethtool -p eth0 and replug the cables.

> Subsequent cold starts only read the files

No they don't. Thare no files to read. You just wrote above in your commetn that the first time OS boots ifcfg are generated. So after a machine is coldstarted there are no ifcfg files! They are generated once per coldstart and saved. Then during each restart those files are read and everything is fine.

Now, I was saying, you can have a provisioning scheme where during coldstart, in your kickstart file you can fetch and write stable ifcfg files to prevent machines from creating their own. What we do instead is install a custom RPM with a udev script where an algorithm sorts the network interfaces in a stable way (since we only deal with a known and limited set of motherboards and network cards).

[nailer]

> No they don't. Thare no files to read. You just wrote above in your commetn [sic] that the first time OS boots ifcfg are generate [sic]. So after a machine is coldstarted there are no ifcfg files!

As long as you don't reinstall your OS, or lose your data, your config files are there. Cold starting hardware does not delete data.

Are you trolling?

[adobriyan]

> Network interfaces should not rename themselves after reboots.

But that's because PCI bus walk order doesn't change across reboots.

[rdtsc]

Well it depends. There is a kernel parameter that forces a consistent walk order:

   pci=bfsort

It forces breadth-first device sorting.

But otherwise I understand that devices are detected in parallel and whichever ones return first are designated eth0, eth1 etc.

We had this problem on some machine that have 4+ eth0 devices. We use RHEL|CentOS 5.x (see in the post above how we solved the problem).

[moe]

This!

I once had a server (in the pre-udev era) that would occasionally shuffle its network devices after reboots. I don't remember how I fixed it but I do remember the short phase of amusement, followed by a longer phase of frustration.

[mansr]

Moving a PCI card to another slot should also not rename the device. With a typical current udev setup, device names are persistent based on MAC address. With this proposal, either the name will change if the bus topology changes, or bus location based names will be _wrong_. As usual the fedora/desktop trolls are breaking perfectly good things for no apparent reason at all.