Hi Jan, thanks for the quick answer. > On Wednesday 2011-05-18 17:58, Detlev Zundel wrote: > >>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. > > On the contrary. This should exactly do what is requested: changing > the dst address in the packet to 255, and you should be able to > observe that this address change was successful by using -j LOG in > filter-INPUT. > >>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. > > By the very definition of broadcast, a receiver is not to route it > any further, wh. As such, it enters INPUT. No loss, the machine > properly receives it (as it is supposed to). OUTPUT is only for > locally-generated packets, but received frames can only appear in > INPUT or FORWARD. Yes, sorry, I really meant that I did not see anything on the FORWARD chain. > Netfilter does not even play a role in this. > > All the bcast/mcast forwarders are userspace AFAICS. Ok, thanks for the explanation, this now all makes sense to me and I'll turn to userspace. Best wishes Detlev -- It is practically impossible to teach good programming to students that have had a prior exposure to BASIC: as potential programmers they are mentally mutilated beyond hope of regeneration. -- Edsger Dijkstra -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
