How to add a "unknown" network with DHCP enabled?

[julianguttzeit]

Hi guys,

at first I love the openmptcprouter and it works great with all MY Components / Modems etc.. But here is the Case.
I stream Events with a 3 LTE Modem bonding. Sometimes there is the opportunity to use the unknown "on location router". So I don't know the configuration and can not access / reconfigure this one. But I think it would be a great to use it as a fourth WAN. Just a little bit more "backup".

Am I able to bypass the eventually activated DHCP and give it a Gateway/IP I can use for bonding?
I read out the routers mac adress and tried to give it a static ip (Gateway: 192.188.40.1 and IPv4: 192.168.40.2). I configured these IPs in the assistant for bonding.

Any tipps? Any mistakes in my thinking that I made?

Or do I need to build a "blackbox" (something pi based that takes DHCP from the router and reroutes it to my wanted IPs..) or do some switch configuration, that the DHCP does not interrupt..?

Thank you!
Julian