ccna wan pdf

ccna wan pdf.VTP pruning is a Cisco feature that allows the switch to dynamically add and remove VLANs associated with trunk connections, thereby improving the efficiency of switched networks. By default, all VLANs are associated with trunk connections, which means that when a device in any VLAN generates a broadcast, multicast, or unicast with an unknown destination address, the switch floods the frame out of the port associated with the source VLAN, which includes the trunk port. This flooding is necessary in many cases, especially when the VLAN spans multiple switches. However, if an adjacent switch does not have an active port that belongs to the source VLAN, it does not make sense to flood frames to it.1. Trunking without pruningTake a look at a simple example, as shown in Figure 12.8. In this example, VTP pruning is not enabled.PC.A, PC.B, PC.E, and PC.F belong to the same VLAN, and if PC.A generates a broadcast, Switch A will forward it to the access port to which PC.B is connected, as well as to the trunk port (because the trunk port is a member of all VLANs by default). This is logical because both PC-E and PC-F, which are connected to Switch B, belong to this VLANoThere is another VLAN in Figure 12.8 that has two members: PC-C and PC.D. If PC.C generates a local broadcast, Switch A obviously forwards it to the port to which PC-D is connected. However, Switch A also forwards this broadcast to the trunk port connected to Switch B. Considering that none of the devices connected to Switch B belong to this VLAN, this makes no sense and only wastes bandwidth and resources. A sends a video multicast stream at 5 Mbit/s? This could create a throughput problem for that trunk connection because the switch handles multicasts like broadcasts: flooding them out of all the ports associated with the source VLAN.Figure 12.8 VTP pruning is not enabledTo fix this problem, use one of two methods: static VLAN pruning and dynamic VLAN pruning. When using a static configuration, inactive VLANs are manually pruned from the trunk connection on both switches, as shown in Figure 12.9. In this figure, notice that the black VLANs (indicated by dashed lines) are pruned from the trunk connection. The problem with manual pruning is that after adding a member of the black VLAN on Switch B, you must log in to both switches and manually add the pruned VLAN to the trunk connection. o In a network with multiple VLANs and multiple switches, not every VLAN is active on every switch, and accidentally pruning a VLAN from the trunk connection that should not be pruned can lead to connectivity problems. which in turn leads to connectivity problems.Figure 12.9 VLAN Pruning2. Using Trunking with PruningThe VTP pruning feature allows the switch to share additional VLAN information so that inactive VLANs can be pruned from trunk connections. In this case, the switch shares information about which VLANs are active. For example, Switch A tells Switch B that it has two active VLANs (white VLAN and black VLAN) However, Switch B has only one active VLAN and shares this information with Switch Ainformation with Switch A. Based on this shared information, both Switch A and Switch B recognize that the black VLAN is inactive on the trunk connection and should be dynamically removed from the configuration of the trunk connection. The advantage of this feature is that if you activate a black VLAN on Switch B-connect a device to a port on that switch and assign that port to the black VLAN-Switch B will inform Switch A of the new active VLAN, and in turn both switches will dynamically add this VLAN to the configuration of the trunk connection. This allows PC.C, PC-D, and the added device to send frames to each other, as shown in Figure 12.10.