you are getting lan and wans mixed up, or some of the info here is. if it is all on the router side, as in inside your home or office, it is on the lan, and should have an ip address that is like 192.168.x.x or 10.0.x.x.
i am not familiar w/ your particular device, but many dvrs i have seen let you put in the info for it to be a static ip, just put it up high so the dhcp server in your router doesn't try to give out its ip address. there should be a networking area in the menus.
being on the lan side, there would be no reason to forward ports, that would be only if you were going to be viewing the data from the wan (internet) side from outside your location.
what router do you have?