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Re: Proposal v2: enable stateless persistant network interface names

On 25/06/15 23:14, Philipp Kern wrote:
> On the other hand I'm more of a fan of actually naming
> interfaces by their purpose or external labeling. Makes for even less
> mental gymnastics. \-:

You can still do this via manual configuration; as far as I understand
it, nobody is proposing to take away the ability to rename interfaces to
"lan" and "wan", or whatever, selected on the basis of path, MAC
address, driver or any other udev attribute, via udev rules analogous to
those written out by persistent-net-generator.

However, in the absence of manual configuration, *something* needs to
happen, one of:

* the kernel defaults (eth0, ... in arbitrary order)
* the current Debian-specific persistent-net-generator scheme
* one of the various ifnames schemes
* different ifnames schemes depending on device type
  (as implemented in systemd >= 220-5, which uses MAC-based IDs
  for USB and path-based for PCI)

and there are some additional considerations that might not be obvious
to some readers of this thread:

* the default setup cannot use /var because that might be remote
* the udev maintainers do not want the default to involve
  writing to /etc
* each network device has exactly one name, and no aliases
  (kernel limitation)
* renaming to ethN or wlanN, where N is a small integer, cannot
  work reliably regardless (because it can race with the kernel
  assigning the same ethN/wlanN name to different hardware; this
  is why ifnames never assigns names in that form)

To some extent, all of this complexity is because network devices aren't
device nodes in /dev, so they can't have aliases (symlinks) but must
instead have precisely one name. udev has been able to introduce new
disk naming schemes without breaking old ones, precisely because
symlinks to disk device nodes work fine.


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