ccna r&s cost

ccna r&s cost.Chapter 4 Bridges and Switches 77device must spend processing cycles to handle them. A third solution is to use multicast. For multicast, switches also perform flooding, but they are able to learn which devices want to receive multicast traffic and in turn forward multicast frames to only those devices. This topic is outside the scope of this book; it is a topic covered by the Cisco SWITCH exam (300.115).When deploying a large multicast solution, it is important to ensure that the switch supports advanced multicast features and can intelligently forward multicast trafficrather than having to flood it. You want the switch to forward multicast frames only to end devices that are running multicastapplications and want to receive multicast streams; you do not want the switch to flood multicast to all end devices, especially if the multicast traffic is videoThis is especially true when the multicast traffic is video.2. Switching ExampleTo understand what happens when a switch forwards (rather than floods), consider the example shown in Figure 4.3, where there is a hub and a switch, both of which have some PCs connected.Let's assume that this switch has just booted up, which means that its CAM table is empty. o PC-A generates a frame to PC-C, and the switch receives the frame and looks at its CAM table, but does not find the source MAC address (0000.0A01.AAAA), so it adds that address and port 1 to the CAM table. The switch also looks at the destination MAC address (0000.0A01.CCCC), but does not find it in the CAM table either, so the switch floods this frame out of all other ports (ports 2, 3, and 4).For this example, the switch doesn't really have to do this because PC.C and PC.A are connected to the same hub, but the switch doesn't know that. This is an example of flooding a frame whose destination address is an unknown unicast address. In Figure 4.4, the switch adds an entry to the CAM table and floods the frame. As can be seen from this figure, the switch performs the flooding process and its CAM table now contains an entry (for PC-A). Since the target device, PC-C, is connected to the same hub as PC.A, it will obviously receive this frame.