Vrftjkry

I've got an Arris BGW210-700 residential gateway for an AT&T fiber connection to my house. Under Firewall > IP Passthrough, I have Allocation Mode set to Default Server and Default Server Internal Address set to the IP address of my own router (an Apple Time Capsule).

This set-up works, but I'd prefer the BGW210-700 to be in pure Passthrough mode, i.e., assign the publicly routable IP address to the WAN port of my Time Capsule. Currently, there's a double NAT happening because I'd prefer to configure my WiFi devices from the Time Capsule, so it manages the 192.168.2.x subnet for WiFi.

I can set Allocation Mode to Passthrough and Passthrough Fixed MAC Address to that of my Time Capsule.

My question is: if I do this and the publicly routable IP address is "passed through," then how can I access the BGW210-700 itself? (Currently, I access it via http://192.168.1.254.) I tried something like this once and the BGW210-700 became inaccessible. (I had to reset it to factory defaults to recover.)

The BGW210-700 has 4 ethernet ports on the back: one goes to the Time Capsule. Ideally, I want the other 3 ports to be on the 192.168.1.x subnet and the Time Capsule to serve the 192.168.2.x subnet without double NAT'ing (which IP Passthrough should give me). The devices on the two different subnets never need to talk to each other (with the exception of me being able to access the BGW210-700 itself via WiFi > Time Capsule).

Pictorially:

Fiber -> ONT -> BGW210-700

                * LAN: 192.168.1.254

                |

                +-> Other misc devices (via ethernet cables)

                |   * LAN: 192.168.1.x

                |   |

                |   +-> VOIP box

                |   +-> Security system box

                |   +-> ...

                |

                +-> Time Capsule

                    * LAN: 192.168.2.1

                    |

                    +-> True home network (via WiFi)

                        * LAN: 192.168.2.x

                        |

                        +-> Desktop computer

                        +-> Laptop computer

                        +-> ...

How can I do what I want?