Routing, SNAT and two ISPs

[guillaume <guillaume.riviere@hcm.vsl-vn.com>]

Hi all,

Well, it's seams to be a little bit more complicated than
I thought to loadbalance Internat connection between 2 (different) ISP
lines ...

Here is my problem:

Basically, I need to connect my office to 2 differents ISP (different 
gateways and different DNS ). My linux box is a 3 NICs Box. The problem 
is that, for the first ISP, I don't have static Addresses.

So, I would like to loadbalance, "route" and NAT all my internals Addresses
through thoses 2 ISP except for some addresses and some port numbers 
which will use
only the ISP2.

I would like also to detect dead gateway (maybe I ask for to much ...).

My problem is that SNAT is POSTROUTING. I am lose ...
I don't know if I have to deal with iptable2 loadbalancing or if I can do
this only with netfilter.

Maybe in a first part, I just would like to "statically loadbalance" my 
connections.
I mean, just put rules to (for example)

- route http packets to my first ISP and ssh packets to my second ISP,
- route packets from my internals IP 10.0.0.2-100 to ISP 1
- route packets from my internals IP 10.0.0.101 to ISP2
        (all with NAT, of course)

After, I will deal with a real loadbalancing for a part of my internal 
IP and
for some protocols.

Any Help will be very appreciated,
Thank you in advance,
Guillaume