Directed broadcast forwarding can be useful to send wake-on-LAN (WOL) from a different subnet.

By default Linux kernel doesn't forward directed broadcast
packets unless both of /proc/sys/net/ipv4/conf/all/bc_forwarding
and /proc/sys/net/ipv4/conf/$iface/bc_forwarding are set to 1.

I would like to add the following config options for enabling/disabling directed broadcast forwarding:

# Enable directed broadcast forwarding on this interface
set interfaces $IFACE ip enable-directed-broadcast 

# disable directed broadcast forwarding on all interfaces
system ip disable-directed-broadcast-forwarding

By default the global option is enabled but per-interface option is disabled.
Users can enable directed broadcast forwarding on specified inbound interfaces or completely disable this feature on all interfaces.

An example setup:
User (1.0.0.100/24) ---- (eth0: 1.0.0.1/24) Router (eth1: 2.0.0.1/24) ---- (2.0.0.200/24) Target Host

# By default, a packet with destination address 2.0.0.255 from 1.0.0.0/24 are not forwarded by the router.
# On Router, run
set interfaces ethernet eth0 ip enable-directed-broadcast 
# Now, the router will forward packets with destination address 2.0.0.255 from eth0 to eth1. Target Host will receive a copy of the broadcast packet.