A device can receive multiple copies of the same frame because that frame can arrive
from different segments at the same time. Figure 10.8 demonstrates how a whole bunch
of frames can arrive from multiple segments simultaneously. The server in the figure
sends a unicast frame to Router C. Because it’s a unicast frame, Switch A forwards the
frame and Switch B provides the same service—it forwards the unicast. This is bad
because it means that Router C receives that unicast frame twice, causing additional
overhead on the network.