Turns out I needed to:
- Set a Virtual IP address to something like 10.0.0.2/24 within the same range as the Modem’s UI, but not the same as your required UI address. (desired UI target 10.0.0.1)
- Firewall -> NAT -> Outbound: Interface (required WAN interface)
- IPv4 (set protocols if necessary, I set to ‘any’)
- Source Network: Network address of Internal network (usually LAN) to connect from, to the external (WAN) based device.
- Destination Network: 10.0.0.0/24 (the network range of your external device.)
- Translation set to: “Interface Address”
I was able to connect after I applied these rules. I then promptly deleted it as I was afraid I might have opened up pandora’s box with that big of a network range. (Edit: clarified interface names and rules)