[p2p-hackers] NAT hole-punch keepalive/timeouts

[Gaballo Luca]

A NAT can be:
 - "Outbound refresh": keep the mapping active when a packet goes from 
the internal side of the NAT to external side
 - "Inbound Refresh": keep the mapping active when a packet goes from 
the external side of the NAT to internal side
or both!

Moreover the NAT Mapping Refresh Scope can be:
 - "Per Mapping": refresh for all session on that mapping by any 
outbound traffic
 - "Per Session": refresh on a specific session on that particular 
mapping by any outbound traffic

So, when you refresh with a 20-second period (a good delay) you must 
consider also this.

Have fun,
-- Luca

______________________________________________
Luca Gaballo - France Telecom - R&D Division 
Email: luca.gaballo at rd.francetelecom.com         
Peer networks - Solipsis Project
http://solipsis.netofpeers.net/

Personal web: http://perso.enst.fr/~gaballo <http://perso.enst.fr/%7Egaballo>


David Barrett wrote:

> Ok, next question: What kind of keepalive period do you used to 
> maintain the holes you so meticulously punched?
>
> I'm in the process of testing my NAT hole-punching solution, and I'm 
> finding erratic behavior that I *think* is caused by my holes closing 
> on me.  (Ie, I'm able to receive from a peer for a time, and then I 
> cannot.)  So I'm implementing a keepalive, but I'm unsure of what 
> period to use.  For now I'm just using a fixed 20-second period, but I 
> have no idea if that's high or low.
>
> Another option is to have some kind of adaptive solution that tracks 
> elapsed time between sent and received data (thus estimating the last 
> known 'good' window), but that's a pain I'd prefer to avoid.
>
> Any suggestions?
>
> The IETF BEHAVE group has discussed recommendations from anywhere 
> between 30 seconds 
> (http://list.sipfoundry.org/archive/ietf-behave/msg00441.html) and 15 
> minutes 
> (http://list.sipfoundry.org/archive/ietf-behave/msg00127.html).  But 
> ultimately those are foward-looking discussions, and therefore not 
> relevant.
>
> In the real world, I've seen mention that even 30 seconds is 
> insufficient 
> (http://www.frameip.com/nntp/article-comp-protocols-tcp-ip.php?numero=20119). 
>  Perhaps 20 seconds works 
> (http://www.tisc2001.com/newsletters/322.html), but who knows.
>
> Basically, I'm curious what keepalives you've found work today in your 
> real applications, in the real world.
>
> -david
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