[Bug 1959190] [NEW] Support DuplicateAddressDetection by default

[Lukas Märdian]

Public bug reported:

netplan & networkd only use systemd-networkd's default of
DuplicateAddressDetection=ipv6, thus not checking for IPv4 conflicts.

>From what I know RedHat based systems on the other hand use the arping
tool during ifup in their ifcfg system (ARPCHECK=yes by default) to
check for IP conflicts. In order to reach a similar result in Ubuntu, we
would need to place an override configuration snippet in
/etc/systemd/network/10-netplan-eth0.network.d/override.conf, specifying
an [Address] section and corresponding DuplicateAddressDetection=both
setting for each IP address [0].

This is probably even something that netplan should be doing by default,
but it is not currently.

[0]
https://www.freedesktop.org/software/systemd/man/systemd.network.html#DuplicateAddressDetection=

** Affects: netplan
     Importance: Wishlist
         Status: New

** Affects: netplan.io (Ubuntu)
     Importance: Undecided
         Status: New

** Changed in: netplan
   Importance: Undecided => Wishlist

** Also affects: netplan.io (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1959190

Title:
  Support DuplicateAddressDetection by default

Status in netplan:
  New
Status in netplan.io package in Ubuntu:
  New

Bug description:
  netplan & networkd only use systemd-networkd's default of
  DuplicateAddressDetection=ipv6, thus not checking for IPv4 conflicts.

  From what I know RedHat based systems on the other hand use the arping
  tool during ifup in their ifcfg system (ARPCHECK=yes by default) to
  check for IP conflicts. In order to reach a similar result in Ubuntu,
  we would need to place an override configuration snippet in
  /etc/systemd/network/10-netplan-eth0.network.d/override.conf,
  specifying an [Address] section and corresponding
  DuplicateAddressDetection=both setting for each IP address [0].

  This is probably even something that netplan should be doing by
  default, but it is not currently.

  [0]
  https://www.freedesktop.org/software/systemd/man/systemd.network.html#DuplicateAddressDetection=

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