Originally Posted by TheSharkBait
From all the guides ive read, you need an external ip on the external interface?
The guides on what?
As long as you can configure your modem to pass any
incoming traffic on the interesting ports (HTTP,SMTP, ..)
on to your server there's no need for the set-up you're
trying to achieve ... not that it looks overly complicated
(if the modem hardware supports that kind of thing).