ches will have VLAN 100 configured, and as such will receive broadcasts initiated on that VLAN. However, those without ports assigned to VLAN 100 have no use for the broadcasts. Chapter 6: VLAN Trunking Protocol Switches with ports active in VLAN 100 Switch A Switch Z VLAN 100 Broadcast Figure 6-3. Broadcast sent to all switches in VTP domain On a busy VLAN, broadcasts can amount to a significant percentage of traffic. In this case, all that traffic is being needlessly sent over the entire network, and is taking up valuable bandwidth on the interswitch trunks. VTP pruning prevents traffic originating from a particular VLAN from being sent to switches on which that VLAN is not active (i.e., switches that do not have ports con- nected and configured for that VLAN). With VTP pruning enabled, the VLAN 100 broadcasts will be restricted to switches on which VLAN 100 is actively in use, as shown in Figure 6-4. Switches with ports active in VLAN 100 Switch A Switch Z VLAN 100 Broadcast Figure 6-4. VTP pruning limits traffic to switches with active ports in VLANs Cisco documentation states that pruning is not designed to work with switches in VTP transparent mode. VTP Pruning Dangers of VTP VTP offers a lot of advantages, but it can have some pretty serious drawbacks, too, especially if you're not careful. Imagine a network in an active office. The office is in Manhattan and spans 12 floors in a skyscraper. There is a pair of 6509s in the core, a pair of 4507Rs on each floor in the distribution layer, and 3750 access-layer switches throughout the environment. The total number of switches is close to 100. VTP is deployed with the core 6509s being the only VTP servers. The rest of the switches are all configured as VTP clients. All in all, this is a pretty well-built system, very similar to the one shown in Figure 6-1 (but on a grander scale). Now, say that somewhere along the way, someone needed some switches for the lab and managed to get a couple of 3750s of his own. These 3750s were installed in the lab but were not con