Cisco WS-C2960-24TT-L Software Guide - Page 234
VTP Pruning, Optimized Flooded Traffic with VTP Pruning
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Using VTP Chapter 8 Configuring VLANs 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 Port 2 Flooded traffic is pruned. Port 4 Catalyst 2900 XL or Catalyst 3500 XL Switch 2 Switch 5 Flooded traffic is pruned. Port 5 Port 1 Red VLAN Switch 6 Switch 3 Switch 1 30768 8-12 Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide 78-6511-08