4.8 VTP Pruning
4.8.1 Default behavior of a switch
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).