2222
E1: 0260.8c01.3333
E3: 0260.8c01.4444
0260.8c01.2222
E2
E1
B
D
0260.8c01.3333
MAC Address Table
0260.8c01.4444
E3
Improving Performance with Spanning Tree 47
Figure 2-18 Broadcast Storm
2. Switch A examines the destination address ?¬?eld in the frame and determines that the
frame must be ?¬‚ooded onto the lower Ethernet link, segment 2.
3. When this copy of the frame arrives at switch B, the process repeats, and the frame is
forwarded to the upper Ethernet segment, which is segment 1, near switch B.
4. Because the original copy of the frame also arrives at switch B from the upper Ethernet
link, these frames travel around the loop in both directions, even after the destination
station has received a copy of the frame.
A broadcast storm can disrupt normal traf?¬?c ?¬‚ow. It can also disrupt all the devices on the
switched or bridged network because the CPU in each device on the segment must process
the broadcasts; thus, a broadcast storm can lock up the PCs and servers that try to process
all the broadcast frames.
A loop avoidance mechanism eliminates this problem by preventing one of the four
interfaces from transmitting frames during normal operation, thereby breaking the loop.
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