My DSL modem is a Siemens Speedstream 4200. It is not just a dumb modem, but also a fully-fledged router. I would rather it just act as a dumb modem and forward everything to my Linksys WRT54GL. I tried to do this by setting the Speedstream to forward all TCP traffic on ports 0-65535 to the Linksys, but then I could no longer connect to the internet.
Why would forwarding all the traffic from the DSL modem/router to my Linksys router break the internet connection?