2.2.1 Backwards Learning
nWhen a bridge is first plugged in all its tables are empty.
nEvery frame it receives it has to broadcast.
nAs every frame has both a source and a
destination address it reads the source address of every frame (recall it
operates in promiscuous mode!) and notes the LAN/port it came in
on. This forms an entry in its routing table. E.g., A2-45-63-FE-90-AA -> LAN
1(port 8). Each entry also has a time associated with it (i.e., time it was entered)