well not really a port forwarding, because if the N800 is taking IP through DHCP then the port forwarding will require the ip address to forward the port to. check and see if you have any port triggering tab in you router setup. if not that take the suggession what deeteroderdas suggest and in addition to that, you need to assign the static ip on your N800 advance settings in your connection manager, in that way you will always have the same ip from your router where the port will be forward. IMHO this is not a good idea.