[Bug 1869155] Re: When installing with subiquity, the generated network config uses the macaddress keyword on s390x (where MAC addresses are not necessarily stable across reboots)

[James Falcon]

Tracked in Github Issues as https://github.com/canonical/cloud-
init/issues/3634

** Bug watch added: github.com/canonical/cloud-init/issues #3634
   https://github.com/canonical/cloud-init/issues/3634

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Title:
  When installing with subiquity, the generated network config uses the
  macaddress keyword on s390x (where MAC addresses are not necessarily
  stable across reboots)

Status in cloud-init:
  Invalid
Status in subiquity:
  Fix Released
Status in Ubuntu on IBM z Systems:
  Fix Released
Status in initramfs-tools package in Ubuntu:
  Fix Released

Bug description:
  While performing a subiquity focal installation on an s390x LPAR (where the LPAR is connected to a VLAN trunk) I saw a section like this:
     match:
          macaddress: 02:28:0b:00:00:53
  So the macaddress keyword is used, but on several s390x machine generation MAC addresses are
  not necessarily stable and uniquie across reboots.
  (z14 GA2 and newer system have in between a modified firmware that ensures that MAC addresses are stable and uniquire across reboots, but for z14 GA 1 and older systems, incl. the z13 that I used this is not the case - and a backport of the firmware modification is very unlikely)

  The configuration that I found is this:

  $ cat /etc/netplan/50-cloud-init.yaml
  # This file is generated from information provided by the datasource. Changes
  # to it will not persist across an instance reboot. To disable cloud-init's
  # network configuration capabilities, write a file
  # /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
  # network: {config: disabled}
  network:
      ethernets:
          enc600:
              addresses:
              - 10.245.236.26/24
              gateway4: 10.245.236.1
              match:
                  macaddress: 02:28:0b:00:00:53
              nameservers:
                  addresses:
                  - 10.245.236.1
              set-name: enc600
      version: 2

  (This is a spin-off of ticket LP 1868246.)

  It's understood that the initial idea for the MAC addresses was to have a unique identifier, but
  I think with the right tooling (ip, ifconfig, ethtool or even the network-manager UI) you can even change MAC addresses today on other platforms.

  Nowadays interface names are based on their underlying physical
  device/address (here in this case '600' or to be precise '0600' -
  leading '0' are removed), which makes the interface and it's name
  already quite unique - since it is not possible to have two devices
  (in one system) with the exact same address.

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