Changing IP-network given by CDC_ETHER USB Modem

Hello All!

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 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 into something else.

Sure, you can double NAT, from 192.168.0 to whatever you'd like.

But I don't clearly understand how to do this. Via additional Interface module?

If the ZTE is defined as a WAN interface, the subnet on the LAN side have to be something else than 192.168.0.

If the ZTE is defined as a WAN interface, the subnet on the LAN side have to be something else than 192.168.0.

Yes, ZTE is defined as WAN.
LAN is not is different.

But I have a set of ZTEs and all of them has

That is not good. I'd like to transform them from to something else with "double nat" I guess.

Well you are, but if you mean change the subnet the ZTE's providing, then probably no, unless it can be done by AT commands.

you can try something like this, even though this isn't for your device

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.

PS. Telnet and other ways are not working.

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.

That is requirement by OpenMTCPRouter. Every WAN should have unique addressing. May be it will work with only modems but I'm not sure.

do you then need a different WAN IP, or a different WAN subnet ?

It is stated: You must disable DHCP on your modems and set IP in different networks.

So, currently it looks like this.

I try to did the following thing: add two IPs to the modem interface:

It works more or less OK from SSH:

  1. I can ping and traceroute through this modem interface.
  2. I can do telnet to 80 port. It responses with Bad Request and that is not bad (I expect that this is from the Modem web-interface).

Unfortunately I don't understand how to curl or wget from a concrete interface.

you can specify which interface they should bind to, when making the request.

How come?
ping has -I eth
traceroute has -i eth

that can be used for specifying of concrete interface

OK. curl has a hidden option fo choosing of an interface

curl --interface eth2

So, I can reach modems selecting interfaces.

After a deep research:

  1. Bad thing: It is not possible to do anything with these modems. It is not possible even to re-flash them.
  2. Good thing: they work with openmptcprouter without any problems with their DHCP modes.

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