Vtp Pruning - Cisco WS-C2950-24 Configuration Manual

Chapter 8 Configuring VLANs

VTP Pruning

78-6511-05
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
Flooded traffic
Port
is pruned.
4
Flooded traffic
Switch 5
is pruned.
Switch 6 Switch 3
Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
Switch 4
Port 2
Catalyst 2900 XL or
Catalyst 3500 XL
Switch 2
Port
5
Switch 1
Red
VLAN
Port 1
Using VTP
8-17