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Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
78-15908-01
Chapter 9 Configuring VTP
Understanding How VTP Version 1 and Version 2 Work
Understanding VTP Pruning
Note
Enabling VTP pruning on a VTP version 3 switch enables pruning only on the switch that you enable it
on. VTP pruning is not propagated as it is with VTP version 1 and VTP version 2.
VTP pruning enhances network bandwidth use by reducing unnecessary flooded 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.
Make sure that all devices in the management domain support VTP pruning before enabling it.
Figure 9-1
shows a switched network without VTP pruning enabled. Port 1 on Switch 1 and port 2 on
Switch 4 are assigned to the Red VLAN. A broadcast is sent from the host that is connected to Switch 1.
Switch 1 floods the broadcast and every switch in the network receives it even though Switches 3, 5, and
6 have no ports in the Red VLAN.
Figure 9-1
Flooding Traffic without VTP Pruning
Figure 9-2
shows the same 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 Red VLAN has been pruned on
the links indicated (port 5 on Switch 2 and port 4 on Switch 4).
Switch 4
Switch 5
Switch 3
Switch 6
Switch 1
Switch 2
Port 1
Port 2
Red
VLAN
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