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The default behavior of a switch is to
propagate broadcast and unknown packets across the network. This
behavior results in a large amount of unnecessary traffic crossing
the network.
VTP pruning enhances network
bandwidth use by reducing unnecessary flooding of traffic, such as
broadcast, multicast, unknown, and flooded unicast packets. VTP
pruning increases available bandwidth by restricting flooded traffic
to those trunk links that the traffic must use to access the
appropriate network devices. By default, VTP pruning is disabled.
Figure
shows a switched network without VTP pruning enabled. Port 1 on
Switch 1 and Port 2 on Switch 4 are assigned to the green VLAN. A
broadcast is sent from the host connected to Switch 1.
Switch 1 floods the broadcast and
every switch in the network receives this broadcast, even though
Switches 3, 5, and 6 have no ports in the green VLAN.
Figure
shows a switched network with VTP pruning enabled. The broadcast
traffic from Switch 1 is not forwarded to Switches 3, 5, and 6
because traffic for the green VLAN has been pruned on the links
indicated (Port 5 on Switch 2 and Port 4 on Switch 4).
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