From: "André Marascalchi Zenun" <andre dot zenun at gmail dot com>

> Well from the default configuration of m0n0wall I just have enabled the 
> Captive Portal and change the Wan firewall rule to me be able to browse 
> the webGUI from the wan side.

> The modem that I'm using is the NR041 Linksys Router. This modem can be 
> configured of two different ways. As a Gateway and as a Router. When I 
> enable it as a Router I'm not able to browse any website, but if I 
> configure it as a Gateway I'm able to access the websites!

Simple.  As a gateway, it does NAT.  So m0n0wall knows how to get to it and 
does not care what is behind it.  As a router, it does not do nat.  You will 
need a static route to m0n0wall to include the subnet behind the linksys. 
(And of course the IP addresses scope must be different.

> I have tried with other modem and works fine! I think this was a 
> configuration issue from the linksys router!

Kinda... :-)
                            Lee