 only way to break the loop is by disconnecting the offending links. If you're lucky, the looped port's activity lights will be flashing more than those of the other ports. In any case, you won't be having a good day. MAC Address Table Instability Another problem caused by a looped environment is MAC address tables (CAM tables in CatOS) being constantly updated. Take the network in Figure 8-3, for example. With all of the switches interconnected, and spanning tree disabled, Switch A will come to believe that the MAC address for the PC directly connected to it is sourced from a different switch. This happens very quickly during a broadcast storm, and, in the rare instances when you see this behavior without a broadcast storm, chances are things are about to get very bad very quickly. Switch A CAM table: Switch A MAC: 0030.1904.da60 F0/10 MAC:0030.1904.da60 F0/10 Switch B Switch Switch B CAM table: Switch C CAM table: MAC: 0030.1904.da60 F0/1 MAC: :0030.1904.da60 F0/1 Figure 8-3. MAC address table inconsistencies With this network in place, and spanning tree disabled, I searched for the MAC address of the PC on Switch A using the show mac-address table I include 0.1904. da60 com- mand. I repeated the command as fast as I could and got the following results: 3550-IOS# sho mac-address-table I include 0030.1904.da60 0030.1904.da60 DYNAMIC Fa0/10 3550-IOS# sho mac-address-table I include 0030.1904.da60 0030.1904.da60 DYNAMIC Fa0/10 3550-IOS# sho mac-address-table I include 0030.1904.da60 Chapter 8: Spanning Tree 0030.1904.da60 DYNAMIC Fa0/2 3550-IOS# sho mac-address-table include 0030.1904.da60 0030.1904.da60 DYNAMIC Fa0/3 3550-IOS# sho mac-address-table include 0030.1904.da60 0030.1904.da60 DYNAMIC Fa0/2 3550-IOS# sho mac-address-table I include 0030.1904.da60 This switch is directly connected to the device in question, yet at different times it seems to believe that the best path to the device is via Switch B or Switch C. Remember that a switch examines each packet that arrives on a port and assigns the packet's sour