how to automate undirected UDP broadcast route for linklocal addresses?

Bill Plunkett <bill@xxxxxxxxxxxxx> · Mon, 10 Jun 2024 13:52:08 -0600

I have a yocto-hardknott (systemd v247) embedded system using link local addressing.  Undirected UDP broadcasts (i.e. dest ip = 255.255.255.255) are failing with a 'Network is unreachable' error.  I've been able to fix this with the 'route add' command shown below, but would prefer to automate it with systemd.  Any help is greatly appreciated.
This command allows undirected broadcasts:

route add -net 255.255.255.255 netmask 255.255.255.255 dev eth0

systemd configuration:

[Match]
Name=eth0
KernelCommandLine=!nfsroot

[Network]
DHCP=ipv4
LinkLocalAddressing=ipv4

[DHCP]
ClientIdentifier=mac
RouteMetric=10