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ccna r&s exam cost in india.pc-a pc-d 0000.0a01.aaaa 0000.0a01.ddddFigure 4.8 PC-E generates a broadcast frame4.4.3 LoopsAt the network backbone (or at least where important resources are located), you may want to provide some sort of redundancy in your design solution. This might include providing switch redundancy at Layer 2, which in turn creates a Layer 2 loop in the network, as shown in Figure 4.9. The problem posed by network loops is that when switches flood traffic such as broadcast or multicast, that traffic can propagate forever in the loop, which in turn creates serious utilization problems.In addition, when frames with unknown destination addresses are transmitted in the loop, the switch will update its CAM table with the frame's source address, ultimately presenting the illusion that the source device is connected to another switch, which confuses the switch as to where the source device is actually located. For example, if a device is connected to Switch 3, when it generates a frame, Switch 3 will add the source MAC address of this frame to its CAM table and indicate that it corresponds to the inbound port. If the switch does not know the location of the target device, it will flood this frame to its two uplink ports connectedIf both Switch 1 and Switch 2 do not know the location of the target device, they will both flood this frame to Switch 3. This presents a problem: the switch receives these flooded frames and performs a learning function, which in turn presents the illusion that theSwitch 1 Switch 2Figure 4.9 Layer 2 topology devices that contain loops are connected not to the original port but to the uplink port to Switch 1 or Switch 2.Exam Point In a switched network, if multiple copies of the same unicast frame are present, it may be due to the presence of unexpected loops in a redundant switched topology.Spanning Tree Protocol (STP) is used to avoid these problems. the STP eliminates loops and allows network redundancy. In fact, the loop avoidance process is performed in software. you can avoid Layer 2 loops without disconnecting the cables between the switches. Chapter 13 discusses redundancy in more depth, including some STP protocols.