** Description changed:

+ [Impact]
+ Ubuntu users who make use of IPv4 link-local addresses.
+ 
+ [Test case]
+ 1) Add 'link-local: [ ipv4 ]' to the netplan configuration.
+ 2) Run 'sudo netplan apply'
+ 
+ [Regression Potential]
+ Enabling link local means additional addresses are available on the system, 
usually in the form "169.254.XXX.XXX". This is, in effect, a potential security 
issue if it is enabled on untrusted networks (it gives systems a fairly well 
known, discoverable IP address as attack surface). This is not considered a 
regression from previous releases of Ubuntu given that avahi has been available 
on desktop, with the same potential issue. The availability of extra addresses 
might however mean that the system is considered online or reachable via the 
additonal addresses earlier than previously possible, which may lead to 
confusion for the user.
+ 
+ ---
+ 
  Per https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1717983, link-
  local address support was previously handled via integration between
  avahi-autoipd and dhclient.  systemd-networkd does not invoke dhclient.
  It also has direct support for configuring link-local ipv4 addresses.
  But this support is not enabled by default.
  
  It should be possible for a system configured via netplan to make use of
  link-local ipv4 addresses, without needing to configure systemd-networkd
  directly.
  
  Historically we do not turn on link-local ipv4 support automatically on
  servers (avahi-autoipd not installed by default), and we use link-local
  addresses only as a fallback when dhcp gives no response.  So this
  should likely not be enabled by default, but instead be exposed as an
  additional configuration option in netplan yaml.

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https://bugs.launchpad.net/bugs/1771704

Title:
  support for ipv4 link-local addressing

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