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To: "Cipe" <cipe-l,AT,inka,DOT,de>
Subject: Fw: Question about NAT
From: "Paul Arch" <paul,AT,sdmgroup,DOT,com,DOT,au>
Date: Sun, 19 Oct 2003 11:03:48 +0800

 > >
 > >  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?

  At the moment, I don't think I can :(  I also don't know how often the
 changes occur.  I was going to have software running on the Server, that it
 would ask for information off the Remote Device every 5 minutes.  Now I am
 thinking a better way might be for the Remote Device to check in the
 information every 5 minutes - hence, if the addresses did change, it would
 update that information to the Server - so I could still establish a
 connection From the server to the Remote Device on demand.

  I would love a solution that could detect gateway IP changes without data
!
 Does anyone have any ideas ?

  Regards,

  Paul


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