I use Pi4 with OpenWRT and a set of ZTE MF833R USB modems. All the modems are modern and has a limited interface setting. All of the modems are give 192.168.0.1/24 subnet when they are connected with the Pi4.
Is there a way how can I change the subnet with an additional interface at OpenWRT side? Changing the net from ZTE side is not possible.
For example add an additional NAT that will translate 192.168.0.1 into something else.
Unfortunately it is not possible to change it at ZTE size. The manufacturer closed any possibilities.
Why it is not possible to make additional interface in OpenWRT that will work with ZTE-WAN wit another nat and later can be used for true WAN with necessary network address (from OpenWRT side)? Just guessing. That can be like a workaround.
OpenWRT have to work with whatever subnet the ZTE is providing, but I don't understand why the WAN side have to be unique:ish, and why you'd need the triple NAT - you're already double NATing.