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To: Paul Arch <paul,AT,sdmgroup,DOT,com,DOT,au>
Subject: Re: Question about NAT
From: Les Mikesell <les,AT,futuresource,DOT,com>
Date: 18 Oct 2003 09:41:37 -0500
Cc: Cipe <cipe-l,AT,inka,DOT,de>
In-reply-to: <03e201c3955a$f3d1bcf0$0301050a@xp2100>
Organization:
References: <03e201c3955a$f3d1bcf0$0301050a@xp2100>

On Sat, 2003-10-18 at 04:33, Paul Arch wrote:
>  
>  I have an embedded device out in the field which uses a GPRS
> connection to establish a tunnel to a static IP.  
>  
>  
> REMOTE DEVICE  <-------- NAT GW --------> Internet <--------- SERVER
> (10.2.x.x)                                             (Static IP)
>  
>  
> As far as I know, the GPRS connection (its like WAP for mobile phones)
> is provided via a NAT gateway.  This is OK, and I can get everything
> working fine using dynip and ping on the remote device.  I have
> thought of it as like a road warrier, except its natting its way to
> the internet.
>  
> The thing is, cost for traffic is a big issue on GPRS - 2.2cents per
> 1kB of information sent and received.  And as far as I can tell, I
> need to specify the ping on the Remote Device to update its changing
> NATTED address - am I correct in this thinking ? Is there a way of
> keeping the 'connection' open without requiring the ping ? I am
> starting to think I can't since we are using UDP.
>  

You really only need to send something through the tunnel each
time the public IP changes on the NAT gateway.  This resets the
peer address on the other end so it will be able to send back
later. Can you detect the gateway IP change in some way that
doesn't transmit data?

 ---
   Les Mikesell
    les,AT,futuresource,DOT,com


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