Thinking about UDP and tunneling

Randall Stewart rrs at
Thu Nov 20 09:37:53 PST 2008

On Nov 20, 2008, at 8:50 AM, Max Laier wrote:

> On Thursday 20 November 2008 14:00:11 Randall Stewart wrote:
>> On Nov 19, 2008, at 5:33 PM, Julian Elischer wrote:
>>>> Its not new, its the same ip header..
>>>> Its just you go into the mbuf chain and take out
>>>> the udp header...
>>> well you can't do that at the socket buffer becasue you've discarded
>>> the IP header. It may not even be in the mbufs you have. (though  
>>> it's
>>> unlikely). After you've processed the UDP part the IP part is gone  
>>> so
>>> you'd need to intercept the packet way earlier and then do your
>>> own UDP processing, (or maybe attach the IP header onto it with a
>>> tag).
>> One would definitely  have to do some work in udp_input() not a lot  
>> from
>> what I can tell... but it would take some work.
>> Maybe  good course is to use the socket(9) stuff, but add an option
>> that can set a "by-pass function" if the socket is udp... right
>> after you establish the INP the packet goes to, if the function is
>> set, you engage the bypass...
> This sounds reasonable.  One would only have to replace calls to  
> udp_append in
> udp_input with the by-pass function et voila.  Should be clean  
> enough.  There
> might be some problems with holding the socket lock, though.
> For the record, I don't like all the UDP-tunneling madness either,  
> but it
> seems that we are stuck with it ... so we should at least try to  
> come up with
> a somewhat reasonable implementation for this hackery.


This was along the lines of what I was thinking exactly.. one side
note. I am told by my colleague in SCTP crime (Michael Tüxen) that Apple
has this functional by-pass interface. He has already got the UDP  
code working in the MAC version of our stack :-)

I will start working on this when I get back from the IETF. I need to  
up the NAT support stuff (almost done) and then I will start looking at
the locking issues that this may bring...


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Randall Stewart
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