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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
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Chapter 8 Configuring VLANs
Using VTP
VTP Pruning
Pruning increases available bandwidth by restricting flooded traffic to those trunk
links that the traffic must use to reach the destination devices. Without VTP
pruning, a switch floods broadcast, multicast, and unknown unicast traffic across
all trunk links within a VTP domain even though receiving switches might discard
them.
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 on Catalyst 2900 XL and Catalyst 3500 XL trunk ports. If the
VLANs are configured as pruning-ineligible, the flooding continues. VTP
pruning is also supported with VTP version 1 and version 2.
Figure 8-3
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 Red VLAN has been pruned on the links indicated (port 5 on Switch 2 and port
4 on Switch 4).
Figure 8-3
Optimized Flooded Traffic with VTP Pruning
Switch 4
Switch 5
Switch 3
Switch 6
Switch 1
Catalyst 2900 XL or
Catalyst 3500 XL
Switch 2
Port 1
Port 2
Red
VLAN
30768
Port
4
Port
5
Flooded traffic
is pruned.
Flooded traffic
is pruned.