ation necessary to implement the required changes in the VLAN configuration. When a switch's VTP domain is null, if it receives a VTP advertise- ment over a trunk link, it will inherit the VTP domain and VLAN configuration from the switch on the other end of the trunk. This will happen only over manually configured trunks, as DTP negotiations cannot take place unless a VTP domain is configured. Switches also send advertisement requests when they are reset, and when their VTP domains are changed. To answer the question posed earlier, assuming that both SW1 and SW2 started with the same configuration revision number, whichever switch submits the change first will "win," and have its change propagated throughout the domain, as it will be the first switch to advertise a higher configuration revision number. The changes made on the other switch will be lost, having effectively been overwritten. There will be no indication that these changes were lost or even made. VTP Pruning On large or congested networks, VTP can create a problem when excess traffic is sent across trunks needlessly. Take, for example, the network shown in Figure 6-3. The switches in the gray box all have ports assigned to VLAN 100, while the rest of the switches do not. With VTP active, all of the switches will have VLAN 100 config- ured, and as such will receive broadcasts initiated on that VLAN. However, those without ports assigned to VLAN 100 have no use for the broadcasts. 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 inter-switch 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. Chapter 6