how share a internet connection between interfaces like forward in iptables ?

From:	Pablo Alonso <m0n0mza at gmail dot com>
To:	m0n0wall at lists dot m0n0 dot ch
Subject:	how share a internet connection between interfaces like forward in iptables ?
Date:	Sat, 31 Dec 2005 12:28:29 -0300

if I want forward, from my pppoe connection to an specific ip in other
interface, like forward in iptables, how i do ?
sample: iptables -A FORWARD xxxx
i have defined my interfaces, but i don't know how establish the rules ?.
some howto ?

thanks people !.

juanchoX