[p2p-hackers] UDP Hole Punching through Symmetric NATs

[larytet.8753341 at bloglines.com]

i make it on dayly basis using http://larytet.sourceforge.net/btRat.shtml



--- Peer-to-peer development." <p2p-hackers at zgp.org wrote:
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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