[tor-talk] Why tor doesn't support UDP?

[Lunar]

Yuri:
> It is well known that tor only supports DNS UDP requests, and not
> other UDP.
> 
> Tor could relay UDP through the same path as TCP. And the chosen exit
> node could act as a UDP gateway, much like regular routers relay UDP
> packets from different LAN hosts. Routers substitute source port of
> UDP packets and later map back the ip/port in response packets. It
> could be easily imagined how tor could do just the same.
> When I use the virtual machine connected to network through the tor,
> only http apps work, and all UDP apps fail. Even skype is unable to
> connect.
> 
> So what is the reason that UDP isn't supported?

There are many reasons. I guess patches would be happily discussed if
you had some. SOCKS5 supports UDP, TransPort could be made to support
UDP too. Then there's circuit handling and session tracking — the
connection is never opened or closed with UDP.

But then, the underlying connections between relays are still going to
be TCP. Previous research on switching to datagram designs:
http://static.usenix.org/event/sec09/tech/full_papers/reardon.pdf
https://research.torproject.org/techreports/datagram-comparison-2011-11-07.pdf
https://research.torproject.org/techreports/libutp-2013-10-30.pdf

-- 
Lunar                                             <lunar at torproject.org>
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