I have my Pi Zero W set up as a wireless bridge, bridging from wired eth0 to wireless wlan0; of course, wlan0 operates in AP mode. So far so good. Now I'm noticing that when I forgot to plug in the USB Ethernet adapter for eth0 into my Pi Zero W before boot, it won't be added as a bridge port to my bridge br0 automatically. How can I ensure that eth0 always gets added to the bridge, even if I plug eth0 into the Pi only later?
My /etc/network/interfaces has to say this:
auto eth0
allow-hotplug eth0
...
auto br0
bridge_ports eth0 wlan0
...
When I hot-plug eth0 then brctl show only shows wlan0 for br0, but not eth0.