When a frame arrives at a switch interface, the destination hardware address
is compared to the forward/filter MAC database. If the destination hardware
address is known and listed in the database, the frame is only sent out the
correct exit interface. The switch does not transmit the frame out any interface
except for the destination interface. This preserves bandwidth on the
other network segments and is called
frame filtering
.
If the destination hardware address is not listed in the MAC database,
then the frame is broadcasted out all active interfaces except the interface the
frame was received on. If a device answers the broadcast, the MAC database
is updated with the device location (interface).