You have a routing problem.
What Linux are you using (or are you using Network Manager daemon by default)?

Please post the results of the following commands on:

ifconfig.
route -n

You probably need to give your eth0 interface a static address. ppp0 obtains an address through DHCP. Then you'll have to enable packet forwarding and set up IPTABLES appropriately. This can be done using 4 commands then you'll be good to go - but you'll need results of those two commands.

rgds,
Bernard

From: Jonathan McLean <jmmcl2@gmail.com>
To: skunkworks@lists.my.co.ke
Sent: Monday, June 22, 2009 4:59:26 AM
Subject: [Skunkworks] Question - How can I configure my desktop to turn into a pass through for my 3G mdoem

Hey Skunks-

Ok, this one is for the networking peeps out there.  Any help would be great!

Situation:
I have a small LAN set up and is currently serviced by a 4-port D-Link
Wired Router and a D-Link Switch.  1 of these machines is the
administrator machine (ie, mine) and has the tricky task of needing to
talk to both the LAN and the Internet.  I currently use a Safaricom 3G
USB Dongle Modem (Huawei e160) to connect to the internet.  However,
Whenever it is talking to the internet, it does not allow me to talk
to the LAN over the ethernet port.  Frustrating, especially when
trying to research + push out updates and whatnot.




What I want (I think):
What I would like to do is set up an internet sharing scheme without
changing the LAN configuration.  Basically, I want to connect my USB
modem into the admin machine, which then connects to the routers WAN
port, which then shares the connection with everyone else (not for
constant use, that being unrealistic, not even telling people the
machines can go online...).  I am new to these more advanced
networking techniques and I am not quite sure if I should be looking
at bridging, PPPoE or simply more advanced routing tables.  This is
where I need help.  The admin machine will not be a dedicated router,
so the most lightweight solution would be nice.  And it needs to be
able to talk to the LAN and the Internet at the same time.  The D-Link
router will serve as DHCP for the LAN. The admin machine is running
Linux.  Here's a nice flow chart:

Internet <--> USB Modem <--> Admin Desktop <--> Ethernet <--> D-Link
Router <--> D-Link Switch <--> LAN Machines

Of course, suggestions on altering my strategy are also welcome!

Cheers!
--
jonathan mclean
us peace corps volunteer
ict specialist
mtongwe, kenya
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