[tproxy] TPROXY for a UDP listener

Hi, I have a linux router that would receive UDP packets through a GRE tunnel that is not destined for the router itself. I'm hosting a UDP listener that is supposed to intercept these UDP packets and reply to them accordingly. What I'm seeing is that the UDP replies (sent by this intercepting process) are being source by the real IP address of the linux box itself and of course the remote end just drops these replies since they do not conform to the src/dst IP and port of the originating socket. So basically my UDP listener does get the UDP requests but the replies have an incorrect src/port. I followed this documet:for the setup: http://www.mjmwired.net/kernel/Documentation/networking/tproxy.txt Can someone help please? -- Ramin