Well, depend on your ISP. Some ISPs use static, most ISPs use Dynamic DHCP. However some ISPs have modems with built in routers which changes what the WAN IP address gets on the 850L router. If it's a private IP address from the ISP modem, 192.168.0.Something, then Port forwarding will not work correctly. If the ISP Modem is a stand alone modem and the ISP gives a public IP address, like 23.54.129.254 for example, to the 850L router, then port forwarding and other router features should work IF they are configured correctly ON the router.