[tproxy] TProxy with UDP

Maximilian Frank mail at frank-maximilian.at
Mon Jun 26 15:54:00 UTC 2017

Hi List,

not sure if I am in the right place as tproxy is part of the kernel now,
but i am gonna as here anyway.

I am currently building a python based transparent TCP + UDP proxy. The
setup for the proxy would be a basic mitm i.e.

Local Net --> Tproxy Box --> Internet

For TCP i can simply use getsockopt(SO_ORIGINAL_DST) to get original
destination address and port. This works for tproxy and normal
redirects. With UDP of course i cant do that. At the moment i am using
IP_RECVORIGDST to get the original udp destination and port. This works
fine apart from the fact that there seems to be a bug in recent kernels
disabling this sockopt.

While researching tproxy i found this mail
(https://lists.balabit.hu/pipermail/tproxy/2008-November/000996.html) in
the thread archive. My question now is this udp accept part of the
kernel version of tproxy or is there a patch for it out there for newer
kernels. I ask because i feel this approach is a lot cleaner than me
manually creating a new tproxy enabled socket.  So any info/help is much

with kind regards,

Maximilian Frank

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