I would like to rewrite the contents/payload of UDP packets as they are received by a machine, on selected reports - before they are passed to the listening application.

For example, I would like to change the headers of a UDP-based protocol by using grep-like regular expressions (to add, remove or change parts of each message received).

Is this possible with a software firewall or similar tool?

Thanks all!


If this isn't for production, but rather just learning. I recommend Scapy, you can craft and replay packets on a object oriented interface that relates to the OSI model. It acts like an interactive python console. You can also sniff with it, lots of fun ;-)


Such a tool is called a UDP Proxy and there are a few out there.

  • Simple UDP Proxy/Pipe
  • udpproxy
  • UProxy
  • Thanks, DigitalRoss. These last two look like they do forwarding of UDP only, rather than allowing rewrites of the payload. Is that so? What do you mean by "Simple UDP Proxy/Pipe". Pipe to a userland program? – wodow Oct 30 '09 at 16:36
  • Ah, I see it is actually the name of a package! – wodow Oct 30 '09 at 16:38

TRIPP may also be a solution:


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