I have a Rasberry Pi with two network interfaces.
One is a ppp interface connecting to a cellular modem over USB.
The other is a local ethernet connection with an ethernet cable connected to a local device.
The ppp interface works well when I start a systemd service to connect to it on boot-up.
However, as soon as I plug in the ethernet cable and boot the device, the eth0 interface and ppp both show up on ifconfig, but with the ppp interface I can not connect out to anything, for example ping 220.127.116.11 states that the destination is unreachable. If I plug out the ethernet cable tho again, it works fine.
Any idea what is going wrong here and why the two connections are not working at the same time? Thanks