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Re: NAT Configuration for Dual WAN Router

  • From: Peter Dambier
  • Date: Thu Dec 15 04:51:13 2005

Joe Johnson wrote:
I've been trying over and over to figure this one out, but I'm just hitting
the end of my wits. We have a remote office that can only get 768Kbps DSL,
which they've not totally maxed out. So management's solution now is to buy
a second DSL line, but they won't let me buy a dual WAN router (in case they
add a 3rd DSL line).
I've found some great articles on how to get the interfaces working with 2
default gateways (I used this:
s) and that is all running fine. It alternates every few minutes which WAN
port is used when I traceroute (which is fine) and everything is
connecting fine from the router. However, I can't figure out how to get NAT
running on the server for the 2 WAN ports for clients inside the LAN. I can
NAT to 1 DSL, but that is useless.
What I am looking for is a tutorial in how to do this or a pointer to
someone who can help. Anyone know of a resource for this?
Joe Johnson
[email protected]

I dont see how the router can NAT to more than one ip-address. So you need
one NAT-router per DSL-line.

Now use your linux, without NAT, to distribute the traffic.

Make a guess where most of your goes. Get some vague ip-address ranges and
divide them. E.g. send all traffic to microsoft via router-1 and all traffic
to cnn via router-2.

Both your clients and your linux router dont know about the NAT.

The routers, up to 500 of them :) dont know nothing except NAT.

If your clients are in then it might be a good idea to
put the NAT-routers in

No need for the routers to talk to eachother. Your linux router needs a
virtual interface on say to talk to each router.

It would be good to have a real interface for each router to the linux
and to have a separate one for your clients. But the linux is intelligent
enough and those 1 MBit dsl lines are slowly enough that you can put
everything together on one switch. No need to bother which line is which...

10 MBit is fast enough to the outside.

Another aproach:

Can you split your costumers into separate networks that dont talk to
eachother? Then give each group its own NAT-router and give your
servers two or more interfaces to make them part of both networks.
You must put the routers in different networks of course, say and

Use an

Then you run one linux for each dsl-line.
Those linuxes know how to route internally too.
Now you simply distribute the clients between the linuxes.

Dont ask the price. Your management will be delighted :)

This solution will allow you some 8 dsl-lines. If you need more
buy another bladecenter and connect them.

Peter and Karin Dambier

Peter and Karin Dambier
The Public-Root Consortium
Graeffstrasse 14
D-64646 Heppenheim
+49(6252)671-788 (Telekom)
+49(179)108-3978 (O2 Genion)
+49(6252)750-308 (VoIP:
mail: [email protected]
mail: [email protected]