Chapter 14 Configuring VTP

Understanding VTP

VTP pruning blocks unneeded flooded traffic to VLANs on trunk ports that are included in the pruning-eligible list. Only VLANs included in the pruning-eligible list can be pruned. By default, VLANs 2 through 1001 are pruning eligible switch trunk ports. If the VLANs are configured as pruning-ineligible, the flooding continues. VTP pruning is supported with VTP Version 1 and Version 2.

Figure 14-1shows a switched network without VTP pruning enabled. Port 1 on Switch A and Port 2 on Switch D are assigned to the Red VLAN. If a broadcast is sent from the host connected to Switch A, Switch A floods the broadcast and every switch in the network receives it, even though Switches C, E, and F have no ports in the Red VLAN.

Figure 14-1 Flooding Traffic without VTP Pruning

Switch D

Port 2

Switch E

Switch B

Red

VLAN

Port 1

Switch F

Switch C

Switch A

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Figure 14-2shows a switched network with VTP pruning enabled. The broadcast traffic from Switch A is not forwarded to Switches C, E, and F because traffic for the Red VLAN has been pruned on the links shown (Port 5 on Switch B and Port 4 on Switch D).

Figure 14-2 Optimized Flooded Traffic with VTP Pruning

 

 

 

 

 

Switch D

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Port 2

Flooded traffic

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

is pruned.

 

 

 

 

Port

 

 

 

 

 

 

 

 

 

 

4

 

 

 

 

 

 

Switch B

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Red

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VLAN

Switch E

Flooded traffic

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

is pruned.

Port

 

 

 

 

 

 

 

 

 

 

5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Port 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch F

Switch C

 

 

Switch A

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Catalyst 3750-E and 3560-E Switch Software Configuration Guide

 

OL-9775-02

14-5

 

 

 

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Cisco Systems 3750E manual 14-5, Vlan