Network bridge and broadcast ethernet frames

Solution 1:

The bridges act as switches, and send a broadcast frame out every interface except the one where it was received.

The trick with this is the wlan interfaces, which don't behave in the same way as you'd think of a normal interface. A number of clients can be associated, but each client doesn't get sent all traffic - conceptually, think of each associated client as a port on a switch (and while we're at it, feel free to think of an open, unencrypted wireless network as a hub).

R1 will get the frame in br0, which plays switch and will send it to wireless clients except the one that sent the frame as well as its eth0, then R2 will get it on br0 and send it to all interfaces except the ingress interface, sending the frame to all associated wireless clients.

IEEE 802 is where all these standards live, but it's not exactly light reading.