Answer
Node A sends the message on LAN1, where every node receives it,
but only bridge $\mathrm{B} 1$ keeps it. All other nodes discard it because it is not
addressed to them. Bridge $\mathrm{B} 1$ removes the message from LAN1 and
rebroadcasts it on LAN2. Every node on LAN2 receives the message, but
again, only bridge $\mathrm{B} 2$ keeps it. All others discard it. Bridge $\mathrm{B} 2$ knows that
node $\mathrm{B}$ is located on LAN3, so it rebroadcasts the message on LAN3, where
node $\mathrm{B}$ receives it, recognizes its own address, and removes the message
from the network. The message has arrived at its intended destination.
Work Step by Step
Node A sends the message on LAN1, where every node receives it,
but only bridge $\mathrm{B} 1$ keeps it. All other nodes discard it because it is not
addressed to them. Bridge $\mathrm{B} 1$ removes the message from LAN1 and
rebroadcasts it on LAN2. Every node on LAN2 receives the message, but
again, only bridge $\mathrm{B} 2$ keeps it. All others discard it. Bridge $\mathrm{B} 2$ knows that
node $\mathrm{B}$ is located on LAN3, so it rebroadcasts the message on LAN3, where
node $\mathrm{B}$ receives it, recognizes its own address, and removes the message
from the network. The message has arrived at its intended destination.
