XBC Help Setups - 2 Router
This is where it gets complicated. You can view the external IP address on the status page.
Modem is connected to first router, which has an ethernet cable leading to the WAN port (IMPORTANT) of the second router. The second router leads to the xbox and computer.
The IP addresses in the Picture are probably wrong, you'll have to find these out yourself (status on router or network connection).
The external IP address can only be set by the DHCP server upline, so router "A" gets it's external IP from the modem, "B" router gets it's external IP from the "A" router.
When you do your port forwarding you must forward to the B router's external address. After this, you can on the B router you can forward normally to the PC.
The problem with the way it is setup now (modem connected to router A's WAN and one of router A's ports connected to one of router B's ports causes you to have two DHCP servers on one network. When your computers connect, they could connect to either DHCP server.
For any kind of advanced networking it will not work. You need a consistent IP address so that you don't constantly have to reconfigure for maybe forwarding through both routers or maybe forwarding directly to the pc from router G.
Ideally when you first setup your network, instead of changing the IP range of the second router, you should have disabled DHCP so that router A was the only router controlling your network. This would have required a lot less configuration
Info contributed from XBC forums.