Yeah, what he said. Trying to access the external IP address from within a NATted network is a relatively complex problem that is relatively difficult to solve, and it's not really a problem that causes much grief, other than having to have multiple DNS zones, which you probably need anyway, in order to not show off your internal addresses to the Internet.

In other words, don't do that. Typical of the Linksys tech support guy to not mention such a basic thing (that they're bound to encounter every day) to you.