Mike,
There are a lot of routers that will not allow a port forward unless the router provided the IP address through DHCP. Of course, then you must bind (reserve) the IP address when doing so. In addition, I found routers that would not forward the ports even if it appeared that you could give an IP address into the port forwarding table without using DHCP, as if the RRC is invisible.
This caused so many problems, that my checklist recommends using DHCP and binding the IP address. This is the only way you can know 100% that it will work under all circumstances. The only time problems occur is when the user forgets to bind the address under DHCP.
73,
Mitch DJ0QN / K7DX