two ISP but only one NAT

["Ethy H. Brito" <ethy.brito@inexo.com.br>]

Hi All

Let's see if I can make that clear.

I have two ISP. ISP-A gave me just one IP and ISP-B gave a hole class-C.
Both ISPs are connected to a Linux Router via ethernet cards

I need that connections originated inside my Class-C be "NATed" thru
ISP-A IP.
And connections from outside to one of my Class-C IPs be NOT "NATed" when
outgoing.

i.e it must be possible to someone outside my Class-C to connect to some
host inside it without "NATing" the packages that goes out.

something like (i did not tried that. I am still wondering how to)

iptables -t nat -A PREROUNTING -o ISP-A \
                -m state --state  NEW \
                -j SNAT --to_source SOME_IP 

(will this rule continue to NAT the packets that follows the NEW one (the
ESTABLISHED or RELATED ones for instance)?

Fuzzy??

Regards

Ethy