How do I configure a wireless router so I can still access the modem configuration service on the WAN port?

I just bought a new Linksys wireless router and want to configure it, securely, to allow access to the modem's configuration web page/service. The modem is of course plugged into the WAN port on the router. I'm sure that the Linksys router's software is very common across many variants of their routers, however, if I could probably get things setup with some basic general guidance.

I want it to be secure of course. Perhaps eventually I might want to provide single point forwarding so I can access a specific machine within the home LAN while I'm away. I really think I'm not understanding something fundamental because it seems logical that I should be able to configure the router without having to use tunneling or advanced routing configurations so that I can access the modem's configuration. I believe that the router's NAT is getting in the way.

From serverfault Citizen Dos

• You need to identify the type of service/modem (e.g. cable, DSL, etc.). In most cases, there is very little, if any, additional configuration needed with a properly bridging modem - which is the default for high speed cable.

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