UDP DNAT to a broadcast address

[Detlev Zundel <dzu@denx.de>]

Hi,

looking for the answer to this problem, I searched the web and this
mailing list, but I still couldn't find a definitive answer to the
question that I have.

In my setup I need to a UDP packet sent to the external IP of my router
to trigger a broadcast UDP packet on the local network and relay back
the answers to this packet.

It looks like this should do the trick:

iptables -t nat -I PREROUTING -i ppp0 -p udp --dport 3333 -j DNAT --to 192.168.0.255

Of course, as I write this e-mail, this does not work.  I can see the
packets entering the INPUT chain, but I see no packets on the OUTPUT
chain.  I speculate that this is because braodcast addresses are not
routable and thus the packet gets lost somewhere.

Is there any method to solve this with netfilter or do I need to write a
bi-directional UDP proxy in userspace?

Thanks
  Detlev

-- 
(3)   With sufficient thrust,  pigs fly just fine.  However, this is not
necessarily a good idea.  It is hard to be sure  where they are going to
land, and it could be dangerous sitting under them as they fly overhead.
                              -- The Twelve Networking Truths (RFC 1925)