Smartphone USB Tethering

Hi,

I tried smartphone Tethering as I will switch providers soon and during that I'd like to use the Android smartphone during the switch-over process (which would disconnect the main line). However this doesn't work.

mySetup
openwrt router connected to DSL router (modem+router). eth0 is in subnet 192.168.0.1/24 just like the router. Its not double-NATted but there is a static route setup in the DSL router. (BR-LAN is 192.168.1.1/24) Behind openwrt are the devices (connected via BR-LAN). openwrt acts as router only, no dhcp no dns (there is another dhcp/dns in the lan)

I used the wiki page (https://openwrt.org/docs/guide-user/network/wan/smartphone.usb.tethering) and installed the kmod-usb-net-rndis on the openwrt (fritzbox 4040 with openwrt 21.02). The smartphone itself is recognized and I get an IP adress from its dhcp server on the hw interface usb0. Also if I disconnect my mainline (changing the device to usb0 on the WAN interface) I can hop on via ssh to the openwrt from a client and run there "ping google" and it resolves the adress and icmp works to the google servers. But when i try from client (that is in subnet of openwrt router br-lan) I can't even ping 8.8.8.8
I know that the smartphone tethering works also if attached to other clients directly, it seems to be something on the openwrt not forwarding the packets?

I remember in the past i managed to get it working, however i believe i had a routed phone back in the day and fiddled with the routes in the phone, but its too long ago (i think i did some route add commands)
Do I also need to add a forwarding on the smartphone like i had to do on the dsl router? How would I even do that on an unrooted phone? Or do I need to put my clients in the same subnet as the opnwrt usb0 interface is in?

Thanks for helping me out

Turn masquerading back on on wan. There is no way to add routes in a smartphone so you have to NAT from the LAN to the phone's network to serve the LAN.

Your choicre to not upgrade you will allso need ancient android to work with ancient rndis driver.
For supported version - bring old wan down, new wan up and you are ready.