Comment 12 for bug 1914740

systemd-networkd has this option in systemd.network

RequestBroadcast=
           Request the server to use broadcast messages before the IP address has been
           configured. This is necessary for devices that cannot receive RAW packets, or
           that cannot receive packets at all before an IP address has been configured. On
           the other hand, this must not be enabled on networks where broadcasts are
           filtered out.

I wonder if in addition to netplan.yaml, one could manually create /etc/systemd/network/NETPLAN_GENERATED_NETWORK_NAME.network.d/ directory
and drop in there 30-request-broadcast.conf

[DHCPv4]
RequestBroadcast=yes

I wonder if that will make "everything work"

Note that indeed this will only work for installed systems to communicate with each other. This will not work from the initrd to netboot the installer (aka ip=dhcp url=http://url/to/server-live.iso).

I am slightly perplexed about this option. Is it possible to detect that interface is a hypersocket in L3? Shouldn't systemd-networkd default to RequestBroadcast=yes for such interfaces? Imho it would be not neat that one has to manually specify request-broadcast: true in netplan yaml.