[p2p-hackers] UDP Hole Punching through Symmetric NATs

Lemon Obrien lemonobrien at yahoo.com
Wed Jun 15 20:24:12 UTC 2005


i downloaded Rodi source code. I checked out how the NAT stuff worked...and well, didn't understand it too well. it seemed it was using a thread to send messages to itself so it could discover its global port?
 
would you mind explaining how it works in detail?
 
lemon

larytet.8753341 at bloglines.com wrote:
i make it on dayly basis using http://larytet.sourceforge.net/btRat.shtml



--- Peer-to-peer development." 
In my ongoing
quest for real-world data, do you know of any significant 
> P2P deployments
that hole-punch through symmetric NATs?
> 
> 
> As you know, the simple
"rendezvous" hole-punching approach described by 
> Bryan Ford's paper [1]
suggests that upwards of 82% of all NATs can have 
> holes punched on the
assumption that "consistent endpoint translation" 
> is in place (and thanks
to the IETF-BEHAVE group, this number will only 
> improve). This means
if you establish outbound UDP sessions from the 
> same private endpoint
to two separate locations, your NAT will assign 
> the same public endpoint
to each. This allows me to contact you without 
> "guessing" what NAT
port you might be using.
> 
> [1] http://www.brynosaurus.com/pub/net/p2pnat/

> 
> But as Bryan describes, symmetric NATs make no such consistent 
>
translation, and thus each outbound session is assigned a unique public 
> endpoint by the NAT. This complicates hole punching, but doesn't 
> prevent
it. To punch through symmetric NATs you must, based on 
> knowledge of one
of a peer's public NAT endpoints, intelligently guess 
> the others.
> 

> 
> So hole punching through symmetric NATs is difficult, and Bryan suggests

> not worth the effort. I'm curious what you think, however. Have you

> tried it and found it useful in the real world?
> 
> In theory it can
get you better than 82% success ratio of hole punching, 
> but I'm not sure
if it gets you only to 85% or 90% or 99% or what. Do 
> you know of any
success (or failure) stories of hole punching through 
> symmetric NATs in
the real world?
> 
> -david
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> 
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You don't get no juice unless you squeeze
Lemon Obrien, the Third.
		
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