8-4
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
78-14064-04
Chapter 8 Configuring VTP
Understanding How VTP Works
Figure 8-1 shows a switched network without VTP pruning enabled. Interface 1 on network Switch 1
and port 2 on Switch 4 are assigned to the Red VLAN. A broadcast is sent from the host connected to
Switch 1. Switch 1 floods the broadcast, and every network device in the network receives it, even
though Switches 3, 5, and 6 have no ports in the Red VLAN.
You enable pruning globally on the Cisco 7600 series router (see the “Enabling VTP Pruning” section
on page 8-7). You configure pruning on Layer 2 trunking LAN ports (see the “Configuring a Layer 2
Switching Port as a Trunk” section on page 7-8).
Figure 8-1 Flooding Traffic without VTP Pruning
Figure 8-2 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).
Figure 8-2 Flooding Traffic with VTP Pruning
Catalyst series
Switch 4
Catalyst series
Switch 5
Catalyst series
Switch 3
Catalyst series
Switch 6
Catalyst series
Switch 1
Catalyst series
Switch 2
Interface 1
Interface 2
Red
VLAN
31074
Switch 4
Switch 5
Switch 3Switch 6 Switch 1
Switch 2
Interface 1
Interface 2
Red
VLAN
31075
Interface 4
Interface 5
Flooded traffic
is pruned.
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